Hydrogen Sulfide Is a Mediator of Cerebral Ischemic Damage

Role of hydrogen sulfide in health and disease

In the past, hydrogen sulfide (H2S) was recognized as a toxic and dangerous gas; in recent years, with increased research, we have discovered that H2S can act as an endogenous regulatory transmitter. In mammals, H2S-catalyzing enzymes, such as cystathionine-β-synthase, cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase, are differentially expressed in a variety of tissues and affect a variety of biological functions, such as transcriptional and posttranslational modification of genes, activation of signaling pathways in the cell, and metabolic processes in tissues, by producing H2S. Various preclinical studies have shown that H2S affects physiological and pathological processes in the body. However, a detailed systematic summary of these roles in health and disease is lacking. Therefore, this review provides a thorough overview of the physiological roles of H2S in different systems and the diseases associated with disorders of H2S metabolism, such as ischemia-reperfusion injury, hypertension, neurodegenerative diseases, inflammatory bowel disease, and cancer. Meanwhile, this paper also introduces H2S donors and novel release modes, as well as the latest preclinical experimental results, aiming to provide researchers with new ideas to discover new diagnostic targets and therapeutic options.

A meta-analysis of animal studies evaluating the effect of hydrogen sulfide on ischemic stroke: is the preclinical evidence sufficient to move forward?

Hydrogen sulfide (H2S) is a gasotransmitter that has been studied for its potential therapeutic effects, including its role in the pathophysiology and treatment of stroke. This systematic review and meta-analysis aimed to determine the sufficiency of overall preclinical evidence to guide the initiation of clinical stroke trials with H2S and provide tailored recommendations for their design. PubMed, Web of Science, Scopus, EMBASE, and MEDLINE were searched for studies evaluating the effect of any H2S donor on in vivo animal models of regional ischemic stroke, and 34 publications were identified. Pooling of the effect sizes using the random-effect model revealed that H2S decreased the infarct area by 34.5% (95% confidence interval (CI) 28.2-40.8%, p < 0.0001), with substantial variability among the studies (I2 = 89.8%). H2S also caused a 37.9% reduction in the neurological deficit score (95% CI 29.0-46.8%, p < 0.0001, I2 = 63.8%) and in the brain water content (3.2%, 95% CI 1.4-4.9%, p = 0.0014, I2 = 94.6%). Overall, the studies had a high risk of bias and low quality of evidence (median quality score 5/15, interquartile range 4-9). The majority of the included studies had a "high" or "unclear" risk of bias, and none of the studies overall had a "low" risk. In conclusion, H2S significantly improves structural and functional outcomes in in vivo animal models of ischemic stroke. However, the level of evidence from preclinical studies is not sufficient to proceed to clinical trials due to the low external validity, high risk of bias, and variable design of existing animal studies.

Pills of Multi-Target H2S Donating Molecules for Complex Diseases

Among the various drug discovery methods, a very promising modern approach consists in designing multi-target-directed ligands (MTDLs) able to modulate multiple targets of interest, including the pathways where hydrogen sulfide (H2S) is involved. By incorporating an H2S donor moiety into a native drug, researchers have been able to simultaneously target multiple therapeutic pathways, resulting in improved treatment outcomes. This review gives the reader some pills of successful multi-target H2S-donating molecules as worthwhile tools to combat the multifactorial nature of complex disorders, such as inflammatory-based diseases and cancer, as well as cardiovascular, metabolic, and neurodegenerative disorders.

Sulfide catabolism in hibernation and neuroprotection

The mammalian brain is exquisitely vulnerable to lack of oxygen. However, the mechanism underlying the brain's sensitivity to hypoxia is incompletely understood. In this narrative review, we present a case for sulfide catabolism as a key defense mechanism of the brain against acute oxygen shortage. We will examine literature on the role of sulfide in hypoxia/ischemia, deep hibernation, and leigh syndrome patients, and present our recent data that support the neuroprotective effects of sulfide catabolism and persulfide production. When oxygen levels become low, hydrogen sulfide (H2S) accumulates in brain cells and impairs the ability of these cells to use the remaining, available oxygen to produce energy. In recent studies, we found that hibernating ground squirrels, which can withstand very low levels of oxygen, have high levels of sulfide:quinone oxidoreductase (SQOR) and the capacity to catabolize hydrogen sulfide in the brain. Silencing SQOR increased the sensitivity of the brain of squirrels and mice to hypoxia, whereas neuron-specific SQOR expression prevented hypoxia-induced sulfide accumulation, bioenergetic failure, and ischemic brain injury in mice. Excluding SQOR from mitochondria increased sensitivity to hypoxia not only in the brain but also in heart and liver. Pharmacological agents that scavenge sulfide and/or increase persulfide maintained mitochondrial respiration in hypoxic neurons and made mice resistant to ischemic injury to the brain or spinal cord. Drugs that oxidize hydrogen sulfide and/or increase persulfide may prove to be an effective approach to the treatment of patients experiencing brain injury caused by oxygen deprivation or mitochondrial dysfunction.

The Hydrogen Sulfide Donor AP39 Reduces Glutamate-mediated Excitotoxicity in a Rat Model of Brain Ischemia

The vast majority of stroke cases are classified as ischemic stroke, but effective pharmacotherapy strategies to treat brain infarction are still limited. Glutamate, which is a primary mediator of excitotoxicity, contributes to neuronal damage in numerous pathologies, including ischemia. The aim of this study was to investigate the effect of the hydrogen sulfide donor AP39 on excitotoxicity. AP39 was administered as a single dose of 100 nmol/kg b.w. i.v. 10 min after the restoration of blood flow and 100 min after middle cerebral artery occlusion (MCAO) in male Sprague-Dawley rats. Neurological deficits by Phillips's score, and infarct volume by TTC staining were evaluated (n = 8). LC-MS was used to determine the extracellular glutamate concentration in microdialysates collected intrasurgically and from freely moving animals 24 h and 3 days after reperfusion (n = 6). The expression of proteins involved in the regulation of glutamatergic transmission was investigated 24 h after reperfusion by Western-blot analysis (n = 6). The results were verified by double-immunostaining of brain cryosections (n = 6). The results showed a significant longitudinal decrease in extracellular glutamate concentrations in the motor cortex and hippocampus in MCAO + AP39 rats compared to MCAO rats. Moreover, the administration of AP39 increased the content of the GLT-1 transporter and reduced the content of VGLUT1 in the ischemic core. Upregulation of the GLT-1 transporter responsible for glutamate reuptake from the synaptic cleft, and downregulation of VGLUT1, which regulates glutamate transport to synaptic vesicles, indicate that these are important mechanisms by which AP39 reduces extracellular glutamate concentrations and, consequently, excitotoxicity after ischemia.

Hydrogen sulfide: From a toxic gas to a potential therapy for COVID-19 and inflammatory disorders

COVID-19 has been shown to induce inflammatory disorders and CNS manifestations. Swift and efficient treatment strategies are urgently warranted for the management of COVID, inflammatory and neurological disorders. Hydrogen sulfide (H2S) has been associated with several clinical disorders due to its potential to influence a broad range of biological signalling pathways. According to recent clinical studies, COVID patients with lower physiological H2S had higher fatality rates. These findings clearly demonstrate an inverse correlation between H2S levels and the severity of COVID-19. H2S has been proposed as a protective molecule because of its antioxidant, anti-inflammatory, and antiviral properties. Various H2S-releasing prodrugs, hybrids and natural compounds have been tested for their therapeutic efficacy in viral infections and inflammatory disorders. In this review, I am highlighting the rationale for using H2S-based interventions for the management of COVID-19 and post-infection inflammatory disorders including neuroinflammation. I am also proposing therepurposing of existing H2S-releasing prodrugs, developing new NO-H2S-hybrids, targeting H2S metabolic pathways, and using H2S-producing dietary supplements as viable defensive strategies against SARS-CoV-2 infection and COVID-19 pathologies.

Neuroprotection Is in the Air-Inhaled Gases on Their Way to the Neurons

Cerebral injury is a leading cause of long-term disability and mortality. Common causes include major cardiovascular events, such as cardiac arrest, ischemic stroke, and subarachnoid hemorrhage, traumatic brain injury, and neurodegenerative as well as neuroinflammatory disorders. Despite improvements in pharmacological and interventional treatment options, due to the brain's limited regeneration potential, survival is often associated with the impairment of crucial functions that lead to occupational inability and enormous economic burden. For decades, researchers have therefore been investigating adjuvant therapeutic options to alleviate neuronal cell death. Although promising in preclinical studies, a huge variety of drugs thought to provide neuroprotective effects failed in clinical trials. However, utilizing medical gases, noble gases, and gaseous molecules as supportive treatment options may offer new perspectives for patients suffering neuronal damage. This review provides an overview of current research, potentials and mechanisms of these substances as a promising therapeutic alternative for the treatment of cerebral injury.

Inhibition of cystathionine-gamma lyase dampens vasoconstriction in mouse and human intracerebral arterioles

AIM

In extracerebral vascular beds cystathionine-gamma lyase (CSE) activity plays a vasodilatory role but the role of this hydrogen sulfide (H2 S) producing enzyme in the intracerebral arterioles remain poorly understood. We hypothesized a similar function in the intracerebral arterioles.

METHODS

Intracerebral arterioles were isolated from wild type C57BL/6J mouse (9-12 months old) brains and from human brain biopsies. The function (contractility and secondary dilatation) of the intracerebral arterioles was tested ex vivo by pressure myography using a perfusion set-up. Reverse transcription polymerase chain reaction was used for detecting CSE expression.

RESULTS

CSE is expressed in human and mouse intracerebral arterioles. CSE inhibition with L-propargylglycine (PAG) significantly dampened the K+ -induced vasoconstriction in intracerebral arterioles of both species (% of maximum contraction: in human control: 45.4 ± 2.7 versus PAG: 27 ± 5.2 and in mouse control: 50 ± 1.5 versus PAG: 33 ± 5.2) but did not affect the secondary dilatation. This effect of PAG was significantly reversed by the H2 S donor sodium hydrosulfide (NaSH) in human (PAG + NaSH: 38.8 ± 7.2) and mouse (PAG + NaSH: 41.7 ± 3.1) arterioles, respectively. The endothelial NO synthase (eNOS) inhibitor, Nω-Nitro-l-arginine methyl ester (L-NAME), and the inhibitor of soluble guanylate cyclase (sGC), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) reversed the effect of PAG on the K+ -induced vasoconstriction in the mouse arterioles and attenuated the K+ -induced secondary dilatation significantly.

CONCLUSION

CSE contributes to the K+ -induced vasoconstriction via a mechanism involving H2 S, eNOS, and sGC whereas the secondary dilatation is regulated by eNOS and sGC but not by CSE.

The Ying and Yang of Hydrogen Sulfide as a Paracrine/Autocrine Agent in Neurodegeneration: Focus on Amyotrophic Lateral Sclerosis

Ever since its presence was reported in the brain, the nature and role of hydrogen sulfide (H2S) in the Central Nervous System (CNS) have changed. Consequently, H2S has been elected as the third gas transmitter, along with carbon monoxide and nitric oxide, and a number of studies have focused on its neuromodulatory and protectant functions in physiological conditions. The research on H2S has highlighted its many facets in the periphery and in the CNS, and its role as a double-faced compound, switching from protective to toxic depending on its concentration. In this review, we will focus on the bell-shaped nature of H2S as an angiogenic factor and as a molecule released by glial cells (mainly astrocytes) and non-neuronal cells acting on the surrounding environment (paracrine) or on the releasing cells themselves (autocrine). Finally, we will discuss its role in Amyotrophic Lateral Sclerosis, a paradigm of a neurodegenerative disease.

Elevated plasma sulfides are associated with cognitive dysfunction and brain atrophy in human Alzheimer's disease and related dementias

Emerging evidence indicates that vascular stress is an important contributor to the pathophysiology of Alzheimer's disease and related dementias (ADRD). Hydrogen sulfide (H2S) and its metabolites (acid-labile (e.g., iron-sulfur clusters) and bound (e.g., per-, poly-) sulfides) have been shown to modulate both vascular and neuronal homeostasis. We recently reported that elevated plasma sulfides were associated with cognitive dysfunction and measures of microvascular disease in ADRD. Here we extend our previous work to show associations between elevated sulfides and magnetic resonance-based metrics of brain atrophy and white matter integrity. Elevated bound sulfides were associated with decreased grey matter volume, while increased acid labile sulfides were associated with decreased white matter integrity and greater ventricular volume. These findings are consistent with alterations in sulfide metabolism in ADRD which may represent maladaptive responses to oxidative stress.

Stretchable Electrochemical Sensor Based on a Gold Nanowire and Carbon Nanotube Network for Real-Time Tracking Cell-Released H2S

Hydrogen sulfide (H₂S), as the third gas transporter in biological systems, plays a key role in the regulation of biological cells. Real-time detection of local H₂S concentration in vivo is an important and challenging task. Herein, we explored a novel and facile strategy to develop a flexible and transparent H₂S sensor based on gold nanowire (AuNW) and carbon nanotube (CNT) films embedded in poly(dimethylsiloxane) (PDMS) (AuNWs/CNTs/PDMS). Taking the advantage of the sandwich-like nanostructured network of AuNWs/CNTs, the prepared electrochemical sensing platform exhibited desirable electrocatalytic activity toward H₂S oxidation with a wide linear range (5 nM to 24.9 μM) and a low dete ction limit (3 nM). Furthermore, thanks to the good biocompatibility and flexibility of the sensor, HeLa cells can be cultured directly on the electrode, allowing real-time monitoring of H₂S released from cells under a stretched state. This work provides a versatile strategy for the construction of stretchable electrochemical sensors, which has potential applications in the study of H₂S-related signal mechanotransduction and pathological processes.

Hydrogen sulfide protects retinal pigment epithelium cells against ferroptosis through the AMPK- and p62-dependent non-canonical NRF2-KEAP1 pathway

Oxidative stress-induced ferroptosis of retinal pigment epithelium (RPE) cells contributes to retinal degenerative diseases. The antioxidant molecule hydrogen sulfide (H₂S) regulates oxidative stress response, but its effect on the ferroptosis of RPE cells is unclear. In this study, sodium hydrosulfide (NaHS) was used as an exogenous H₂S donor to intervene tert-butyl hydroperoxide (t-BHP)-induced ferroptosis of APRE-19 cells. We found that NaHS pretreatment attenuates t-BHP-induced oxidative stress and ferroptosis. Analysis of mRNA-sequencing coupled with FerrDb database identified nuclear factor erythroid-2-related factor 2 (NRF2) as a primary target for the cytoprotective role of H₂S. NRF2 inhibitor ML385 reverses the effects of H₂S on ferroptosis. Biochemical analysis revealed that H₂S stabilizes NRF2. H₂S decreases the interaction between NRF2 and KEAP1, but enhances the interaction between KEAP1 and p62. These results suggest that H₂S activates the non-canonical NRF2-KEAP1 pathway. Further study demonstrated that H₂S stimulates AMPK to interact and phosphorylate p62. Additionally, inhibiting AMPK or knocking down p62 blocks the effects of H₂S. We speculate that targeting the non-canonical NRF2-KEAP1 pathway by H₂S-based drug may benefit the treatment of retinal degenerative diseases.

Hydrogen Sulfide Regulates Macrophage Function in Cardiovascular Diseases

Significance: Hydrogen sulfide (H₂S) is an endogenous gasotransmitter that plays a vital role in immune system regulation. Recently, the regulation of macrophage function by H₂S has been extensively and actively recognized. Recent Advances: The mechanisms by which endogenous H₂S controls macrophage function have attracted increasing attention. The generation of endogenous H₂S from macrophages is mainly catalyzed by cystathionine-γ-lyase. H₂S is involved in the macrophage activation and inflammasome formation, which contributes to macrophage apoptosis, adhesion, chemotaxis, and polarization. In addition, H₂S has redox ability and interacts with reactive oxygen species to prevent oxidative stress. Moreover, H₂S epigenetically regulates gene expression. Critical Issues: In this article, the generation of endogenous H₂S in macrophages and its regulatory effect on macrophage function are reviewed. In addition, the signal transduction targeting macrophages by H₂S is also addressed. Finally, the potential therapeutic effect of H₂S on macrophages is discussed. Future Directions: Further experiments are required to explore the involvement of endogenous H₂S in the regulation of macrophage function in various physiological and pathophysiological processes and elucidate the mechanisms involved. Regarding the clinical translation of H₂S, further exploration of the application of H₂S in inflammation-related diseases is needed. Antioxid. Redox Signal. 38, 45-56.

A Case for Hydrogen Sulfide Metabolism as an Oxygen Sensing Mechanism

The ability to detect oxygen availability is a ubiquitous attribute of aerobic organisms. However, the mechanism(s) that transduce oxygen concentration or availability into appropriate physiological responses is less clear and often controversial. This review will make the case for oxygen-dependent metabolism of hydrogen sulfide (H₂S) and polysulfides, collectively referred to as reactive sulfur species (RSS) as a physiologically relevant O₂ sensing mechanism. This hypothesis is based on observations that H₂S and RSS metabolism is inversely correlated with O₂ tension, exogenous H₂S elicits physiological responses identical to those produced by hypoxia, factors that affect H₂S production or catabolism also affect tissue responses to hypoxia, and that RSS efficiently regulate downstream effectors of the hypoxic response in a manner consistent with a decrease in O₂. H₂S-mediated O₂ sensing is then compared to the more generally accepted reactive oxygen species (ROS) mediated O₂ sensing mechanism and a number of reasons are offered to resolve some of the confusion between the two.

Hydrogen sulfide in ageing, longevity and disease

Hydrogen sulfide (H₂S) modulates many biological processes, including ageing. Initially considered a hazardous toxic gas, it is now recognised that H₂S is produced endogenously across taxa and is a key mediator of processes that promote longevity and improve late-life health. In this review, we consider the key developments in our understanding of this gaseous signalling molecule in the context of health and disease, discuss potential mechanisms through which H₂S can influence processes central to ageing and highlight the emergence of novel H₂S-based therapeutics. We also consider the major challenges that may potentially hinder the development of such therapies.

Nitric Oxide Modulation as a Potential Molecular Mechanism Underlying the Protective Role of NaHS in Liver Ischemia Reperfusion Injury

BACKGROUND AND AIM

Liver IR is a frequent clinical complication with high morbidity and mortality. The present study evaluated the possible protective effect of sodium hydrosulfide (NaHS), a H2S donor, in IR-induced hepatic injury and explored the mechanisms of actions of the investigated drug.

METHODS

Male albino rats (200-230 g) were divided into the following groups: group 1:Sham-operated non treated rats, group 2: IR non treated rats, group 3: L-NNA + IR rats, group 4: NaHS + IR rats, group 5: L-NNA + NaHS + IR rats. Blood samples were collected for ALT determination. Liver tissue samples were used for the assessment of GPx, catalase, SOD, MDA, total nitrites and TNF-α. Parts from the liver were fixed in 10% formalin solution for histopathological examination and immunohistochemical examination of iNOS, eNOS and caspase-3.

RESULTS

NaHS protected the liver against IR. This hepatoprotection was associated with normalization of antioxidant enzyme activity and decrease in hepatic MDA, TNF-α and expression of caspase-3 and iNOS.

CONCLUSION

NaHS is hepatoprotective in IR injury. The hepatoprotective effects of NaHS are associated with antioxidant, anti-inflammatory and antiapoptotic effects. These effects are probably mediated via NO modulation.

Hydrogen sulfide content in pregnant women with preeclampsia in late gestation and their newborns

We examined 70 women who were 22-40 weeks pregnant and their newborns. Of these, 15 women with moderate PE made up group 1, 22 women with severe PE-group 2, and 55 women with uncomplicated pregnancy without hypertensive disorders - the control group. Blood was collected from women when they were admitted to the clinic, and blood was taken from newborns for 3-5 days of life. The concentration of hydrogen sulfide was determined by the method of K. Qu et al [17]. There was a decrease in the level of hydrogen sulfide in the blood serum of women whose pregnancy was complicated by severe preeclampsia. In newborns born to mothers with preeclampsia, an increase in the concentration of hydrogen sulfide was detected in the blood, which is probably a compensatory reaction aimed at restoring vascular homeostasis during early postnatal adaptation.

The Slow-Releasing and Mitochondria-Targeted Hydrogen Sulfide (H2S) Delivery Molecule AP39 Induces Brain Tolerance to Ischemia

Ischemic stroke is the third leading cause of death in the world, which accounts for almost 12% of the total deaths worldwide. Despite decades of research, the available and effective pharmacotherapy is limited. Some evidence underlines the beneficial properties of hydrogen sulfide (H₂S) donors, such as NaSH, in an animal model of brain ischemia and in in vitro research; however, these data are ambiguous. This study was undertaken to verify the neuroprotective activity of AP39, a slow-releasing mitochondria-targeted H₂S delivery molecule. We administered AP39 for 7 days prior to ischemia onset, and the potential to induce brain tolerance to ischemia was verified. To do this, we used the rat model of 90-min middle cerebral artery occlusion (MCAO) and used LC-MS/MS, RT-PCR, Luminex^TM assays, Western blot and immunofluorescent double-staining to determine the absolute H₂S levels, inflammatory markers, neurotrophic factor signaling pathways and apoptosis marker in the ipsilateral frontal cortex, hippocampus and in the dorsal striatum 24 h after ischemia onset. AP39 (50 nmol/kg) reduced the infarct volume, neurological deficit and reduced the microglia marker (Iba1) expression. AP39 also exerted prominent anti-inflammatory activity in reducing the release of Il-1β, Il-6 and TNFα in brain areas particularly affected by ischemia. Furthermore, AP39 enhanced the pro-survival pathways of neurotrophic factors BDNF-TrkB and NGF-TrkA and reduced the proapoptotic proNGF-p75^NTR-sortilin pathway activity. These changes corresponded with reduced levels of cleaved caspase 3. Altogether, AP39 treatment induced adaptative changes within the brain and, by that, developed brain tolerance to ischemia.

Association of sulfur content in erythrocytes with cardiovascular parameters and blood pressure

OBJECTIVE

The study aims at assessing the relationship between blood pressure, heart geometry parameters, and the erythrocyte content of sulfur, potassium, chlorine and phosphorus, in a group of patients with laboratory systolic and diastolic blood pressure (SBP, DBP) below 140 or 90 mm Hg, respectively, who were otherwise healthy and untreated.

METHODS

The study group consisted of 42 adults recruited in a primary care setting. The individuals were healthy, not undergoing any therapy and free from smoking. For each individual, data were obtained on: average 24-hour SBP and DBP, left ventricle geometry, complete blood count, lipids profile, fibrinogen, hs-CRP and the erythrocyte concentration of sulfur (S), potassium (K), chlorine (Cl) and phosphorus (P).

RESULTS

Multivariate regression analysis showed statistically significant relationships of diastolic posterior wall thickness (PWTd) and relative wall thickness (RWT) with the concentration ratio of sulfur and potassium (S/K) in erythrocytes: PWTd and RWT increase as the S/K ratio increases. Also, SBP was found to be positively correlated with the S/K ratio.

CONCLUSIONS

The increase in sulfur content in RBCs could be an indicator of the downregulation of nitric oxide (NO) erythrocyte bioavailability exerted by endogenously produced hydrogen sulfide (H2S), and, in consequence, a marker of the development of hypertension and/or adverse changes in heart geometry.

Sulfide catabolism ameliorates hypoxic brain injury

The mammalian brain is highly vulnerable to oxygen deprivation, yet the mechanism underlying the brain's sensitivity to hypoxia is incompletely understood. Hypoxia induces accumulation of hydrogen sulfide, a gas that inhibits mitochondrial respiration. Here, we show that, in mice, rats, and naturally hypoxia-tolerant ground squirrels, the sensitivity of the brain to hypoxia is inversely related to the levels of sulfide:quinone oxidoreductase (SQOR) and the capacity to catabolize sulfide. Silencing SQOR increased the sensitivity of the brain to hypoxia, whereas neuron-specific SQOR expression prevented hypoxia-induced sulfide accumulation, bioenergetic failure, and ischemic brain injury. Excluding SQOR from mitochondria increased sensitivity to hypoxia not only in the brain but also in heart and liver. Pharmacological scavenging of sulfide maintained mitochondrial respiration in hypoxic neurons and made mice resistant to hypoxia. These results illuminate the critical role of sulfide catabolism in energy homeostasis during hypoxia and identify a therapeutic target for ischemic brain injury.

Hydrogen sulfide in longevity and pathologies: Inconsistency is malodorous

Hydrogen sulfide (H₂S) is one of the biologically active gases (gasotransmitters), which plays an important role in various physiological processes and aging. Its production in the course of methionine and cysteine catabolism and its degradation are finely balanced, and impairment of H₂S homeostasis is associated with various pathologies. Despite the strong geroprotective action of exogenous H₂S in C. elegans, there are controversial effects of hydrogen sulfide and its donors on longevity in other models, as well as on stress resistance, age-related pathologies and aging processes, including regulation of senescence-associated secretory phenotype (SASP) and senescent cell anti-apoptotic pathways (SCAPs). Here we discuss that the translation potential of H₂S as a geroprotective compound is influenced by a multiplicity of its molecular targets, pleiotropic biological effects, and the overlapping ranges of toxic and beneficial doses. We also consider the challenges of the targeted delivery of H₂S at the required dose. Along with this, the complexity of determining the natural levels of H₂S in animal and human organs and their ambiguous correlations with longevity are reviewed.

Hydrogen Sulfide: Novel Endogenous and Exogenous Modulator of Oxidative Stress in Retinal Degeneration Diseases

Oxidative stress (OS) damage can cause significant injury to cells, which is related to the occurrence and development of many diseases. This pathological process is considered to be the first step to trigger the death of outer retinal neurons, which is related to the pathology of retinal degenerative diseases. Hydrogen sulfide (H₂S) has recently received widespread attention as a physiological signal molecule and gas neuromodulator and plays an important role in regulating OS in eyes. In this article, we reviewed the OS responses and regulatory mechanisms of H₂S and its donors as endogenous and exogenous regulators in retinal degenerative diseases. Understanding the relevant mechanisms will help to identify the therapeutic potential of H₂S in retinal degenerative diseases.

Hydrogen Sulfide Upregulates Acid-sensing Ion Channels via the MAPK-Erk1/2 Signaling Pathway

Hydrogen sulfide (H₂S) emerged recently as a new gasotransmitter and was shown to exert cellular effects by interacting with proteins, among them many ion channels. Acid-sensing ion channels (ASICs) are neuronal voltage-insensitive Na⁺ channels activated by extracellular protons. ASICs are involved in many physiological and pathological processes, such as fear conditioning, pain sensation, and seizures. We characterize here the regulation of ASICs by H₂S. In transfected mammalian cells, the H₂S donor NaHS increased the acid-induced ASIC1a peak currents in a time- and concentration-dependent manner. Similarly, NaHS potentiated also the acid-induced currents of ASIC1b, ASIC2a, and ASIC3. An upregulation induced by the H₂S donors NaHS and GYY4137 was also observed with the endogenous ASIC currents of cultured hypothalamus neurons. In parallel with the effect on function, the total and plasma membrane expression of ASIC1a was increased by GYY4137, as determined in cultured cortical neurons. H₂S also enhanced the phosphorylation of the extracellular signal-regulated kinase (pErk1/2), which belongs to the family of mitogen-activated protein kinases (MAPKs). Pharmacological blockade of the MAPK signaling pathway prevented the GYY4137-induced increase of ASIC function and expression, indicating that this pathway is required for ASIC regulation by H₂S. Our study demonstrates that H₂S regulates ASIC expression and function, and identifies the involved signaling mechanism. Since H₂S shares several roles with ASICs, as for example facilitation of learning and memory, protection during seizure activity, and modulation of nociception, it may be possible that H₂S exerts some of these effects via a regulation of ASIC function.

A comparison study of the influence of milk protein versus whey protein in high-protein diets on adiposity in rats

High-protein diets are known to reduce weight and fat deposition. However, there have been only a few studies on the efficacy of different types of high-protein diets in preventing obesity. Therefore, the emphasis of this study lies in comparing the efficacy of two high-protein diets (milk protein and whey protein) in preventing obesity and exploring specific mechanisms. Eighty Sprague Dawley rats were divided into two groups and fed with milk protein concentrate (MPC) and whey protein concentrate (WPC) for 12 weeks. Each group was divided into four levels: two low-fat regimens with either low or high protein content (L-14%, L-40%) and two high-fat regimens with either low or high protein content (H-14%, H-40%). The studies we have performed showed that rats treated with MPC at the 40% protein level had significantly reduced body weight, fat weight and fat ratio gain induced by a high-fat diet, while the protein level in the WPC group had no effect on body weight or body fat in rats fed with a high-fat diet. What is more, rats fed with MPC at the H-40% energy level showed a significant decrease in plasma triglyceride, total cholesterol and low-density lipoprotein cholesterol levels and a significant increase in plasma high-density lipoprotein cholesterol levels compared with the H-14% energy level group. In contrast, in the WPC groups, increasing the protein content in high-fat diets had no significant influence on plasma lipid levels. The results of the amino acid composition of the two proteins and plasma showed that the MPC diet of 40% protein level increased the transsulfuration pathway in rats, thereby increasing the level of H₂S. This research work has shown that not all types of high-protein diets can effectively prevent obesity induced by high-fat diets, as effectiveness depends on the amino acid composition of the protein.

Hydrogen Sulfide Overproduction Is Involved in Acute Ischemic Cerebral Injury Under Hyperhomocysteinemia

Objectives

This study aimed to identify the involvement of hydrogen sulfide overproduction in acute brain injury under ischemia/reperfusion and hyperhomocysteinemia.

Methods

In vitro and in vivo experiments were conducted to determine: the effect of sodium hydrosulfide treatment on the human neuroblastoma cell line (SH-SY5Y) under conditions of oxygen and glucose deprivation; the changes of hydrogen sulfide levels, inflammatory factors, energetic metabolism, and mitochondrial function in the brain tissue of rats under either ischemia/reperfusion alone or a combination of ischemia/reperfusion and hyperhomocysteinemia; and the potential mechanism underlying the relationship between homocysteine and these changes through the addition of the related inhibitors. Furthermore, experimental technologies, including western blot, enzyme-linked immunosorbent assay, immunofluorescence, reverse transcription polymerase chain reaction, and flow cytometry, were used.

Results

Our study found that high concentration of sodium hydrosulfide treatment aggravated the decrease in mitochondrial membrane potential, the increase in both mitochondrial permeability transition pore and translocation of cytochrome C, as well as the accumulation of reactive oxygen species in oxygen and glucose deprived SH-SY5Y cells. As a result, neurological deficit appeared in rats with ischemia/reperfusion or ischemia/reperfusion and hyperhomocysteinemia, and a higher water content and larger infarction size of cerebral tissue appeared in rats combined ischemia/reperfusion and hyperhomocysteinemia. Furthermore, alterations in hydrogen sulfide production, inflammatory factors, and mitochondria morphology and function were more evident under the combined ischemia/reperfusion and hyperhomocysteinemia. These changes were, however, alleviated by the addition of inhibitors for CBS, CSE, Hcy, H₂S, and NF-κB, although at different levels. Finally, we observed a negative relationship between the blockage of: (a) the nuclear factor kappa-B pathway and the levels of cystathionine β-synthase and hydrogen sulfide; and (b) the hydrogen sulfide pathway and the levels of inflammatory factors.

Conclusion

Hydrogen sulfide overproduction and reactive inflammatory response are involved in ischemic cerebral injury under hyperhomocysteinemia. Future studies in this direction are warranted to provide a scientific base for targeted medicine development.

Generation of Rat Monoclonal Antibody to Detect Hydrogen Sulfide and Polysulfides in Biological Samples

Hydrogen sulfide (H₂S) is endogenously produced by enzymes and via reactive persulfide/polysulfide degradation; it participates in a variety of biological processes under physiological and pathological conditions. H₂S levels in biological fluids, such as plasma and serum, are correlated with the severity of various diseases. Therefore, development of a simple and selective H₂S measurement method would be advantageous. This study aimed to generate antibodies specifically recognizing H₂S derivatives and develop a colorimetric immunoassay for measuring H₂S in biological samples. We used N-ethylmaleimide (NEM) as an H₂S detection agent that forms a stable bis-S-adduct (NEM-S-NEM). We also prepared bis-S-heteroadduct with 3-maleimidopropionic acid, which, in conjugation with bovine serum albumin, was to immunize Japanese white rabbits and Wistar rats to enable generation of polyclonal and monoclonal antibodies, respectively. The generated antibodies were evaluated by competitive enzyme-linked immunosorbent assay. We could obtain two stable hybridoma cell lines producing monoclonal antibodies specific for NEM-S-NEM. By immunoassay with the monoclonal antibody, the H₂S level in mouse plasma was determined as 0.2 μM, which was identical to the level detected by mass spectrometry. Taken together, these monoclonal antibodies can be a useful tool for a simple and highly selective immunoassay to detect H₂S in biological samples.

The Role of Hydrogen Sulfide in the Development of Tolerance and Dependence to Morphine in Mice

OBJECTIVE

Hydrogen sulfide is an endogenous gaseous mediator that has been indicated to have a role in pain mechanisms. In this study, we aimed to detect brain and spinal cord hydrogen sulfide levels during different phases of tolerance and dependence to morphine and to determine the effects of inhibition of endogenous hydrogen sulfide production on the development of tolerance and dependence.

METHODS

Morphine tolerance and dependence was developed by subcutaneous injection of morphine (10 mg/kg) twice daily for 12 days. Physical dependence was determined by counting the jumps for 20 min, which is a withdrawal symptom occurring after a single dose of naloxone (5 mg/kg) administered intraperitoneally (i.p.). Propargylglycine (30 mg/kg, i.p.), a cystathionine-γ-lyase inhibitor, and hydroxylamine (12.5 mg/kg, i.p.), a cystathionine-β-synthase inhibitor, were used as hydrogen sulfide synthase inhibitors. The tail-flick and hot-plate tests were used to determine the loss of antinociceptive effects of morphine and development of tolerance.

RESULTS

It was found that chronic and acute uses of both propargylglycine and hydroxylamine prevented the development of tolerance to morphine, whereas they had no effect on morphine dependence. Chronic and acute administrations of hydrogen sulfide synthase inhibitors did not exert any difference in hydrogen sulfide levels in brain and spinal cords of both morphine-tolerant and -dependent animals.

CONCLUSION

It has been concluded that hydrogen sulfide synthase inhibitors may have utility in preventing morphine tolerance.

The role of medical gas in stroke: an updated review

Medical gas is a large class of bioactive gases used in clinical medicine and basic scientific research. At present, the role of medical gas in neuroprotection has received growing attention. Stroke is a leading cause of death and disability in adults worldwide, but current treatment is still very limited. The common pathological changes of these two types of stroke may include excitotoxicity, free radical release, inflammation, cell death, mitochondrial disorder, and blood-brain barrier disruption. In this review, we will discuss the pathological mechanisms of stroke and the role of two medical gases (hydrogen and hydrogen sulfide) in stroke, which may potentially provide a new insight into the treatment of stroke.

Protective effect of intermediate doses of hydrogen sulfide against myocardial ischemia-reperfusion injury in obese type 2 diabetic rats

OBJECTIVE

Subjects with type 2 diabetes (T2D) have lower circulating hydrogen sulfide (H₂S) levels following myocardial ischemia and a higher risk of mortality. The aim of this study was to determine the dose-dependent favorable effects of sodium hydrosulfide (NaSH) on myocardial ischemia-reperfusion (IR) injury in rats with T2D.

METHODS

T2D was induced using a high-fat diet (HFD) and low-dose of streptozotocin. Rats were divided into control, T2D, and T2D + NaSH groups. NaSH (0.28, 0.56, 1.6, 2.8, and 5.6 mg/kg) was administered intraperitoneally for 9 weeks. At the end of the study, heart from all rats were isolated and left ventricular developed pressure (LVDP) and the peak rates of positive and negative changes in LV pressure (±dp/dt) were recorded during baseline and following myocardial IR injury. In addition, infarct size as well as mRNA expression of H₂S- and nitric oxide (NO)-producing enzymes were measured.

RESULTS

In diabetic rats, NaSH only at doses of 0.56 and 1.6 mg/kg increased recovery of LVDP (16% and 42%), +dp/dt (25% and 35%) and -dp/dt (23% and 32%) as well as decreased infarct size (44% and 35%). At these doses, NaSH increased expressions of cystathionine γ-lyase (CSE) (440% and 271%) and endothelial NO synthase (eNOS) (232% and 148%) but it decreased the expressions of inducible NOS (iNOS) (55% and 71%). NaSH at 0.28, 2.8 and 5.6 mg/kg had no significant effects on these parameters.

CONCLUSION

NaSH had a bell-shaped cardioprotective effect against myocardial IR injury in rats with T2D. Higher tolerance to IR injury in heart isolated from type 2 diabetic rats treated with intermediate doses of NaSH is associated with higher CSE-derived H₂S and eNOS-derived NO as well as lower iNOS-derived NO.

H2S-releasing amphiphilic dipeptide hydrogels are potent S. aureus biofilm disruptors

As a gasotransmitter, hydrogen sulfide (H2S) has been studied to treat wounds and inflammation, but its potential antimicrobial effects in this context have not been evaluated. An H2S-releasing dipeptide hydrogel (S-FE), and several non-H2S-releasing control dipeptides, (C-FE, C-GE, FBA-FE, and FE where S = S-aroylthiooxime, an H2S donor; C = control, an oxime incapable of H2S release; FBA = 4-formylbenzamide, also incapable of H2S release; and E, F, G = glutamic acid, phenylalanine, and glycine, respectively), were studied to correlate differences in their chemical structures and H2S-releasing abilities with their antimicrobial effects on Staphylococcus aureus bacteria. Dipeptides with Phe (S-FE, C-FE, and FE) self-assembled into nanoribbons in water and displayed β-sheet formation and enhanced fluorescence, while the other two dipeptides (FBA-FE and C-GE) did not form assemblies in water. In vitro experiments with Staphylococcus aureus, which is a commonly found bacterium associated with wounds, showed significant antimicrobial effects from some of the dipeptides. Dipeptide S-FE inhibited bacterial growth more effectively than any of the controls, thereby limiting biofilm formation or disrupting established biofilms. These antimicrobial H2S-releasing dipeptide hydrogels provide a promising new approach to treat wound infections.

Anti-inflammatory, antioxidant, and gaso-protective mechanism of 3α-hydroxymasticadienoic acid and diligustilide combination on indomethacin gastric damage

The co-administration of 3α-hydroxymasticadienoic acid (3α-OH MDA) and diligustilide (DLG) generates a synergist gastroprotective effect on indomethacin-induced gastric damage. However, the related protective activities of the compounds alone (or in combination) remain unclear. In the present study, we evaluated the anti-inflammatory and antioxidative activities, as well as the potential modulation of important gasotransmitters of each compound individually and in combination using the indomethacin-induced gastric damage model. Male Wistar rats were treated orally with the 3α-OH MDA, DLG, or their combination (at a fixed ratio of 1:1, 1:3, and 3:1) 30 min before the generation of gastric mucosal lesions with indomethacin (30 mg/kg, p.o.). Three hours later, the gastric injury (mm²) was determined. Results from these experiments indicate, in addition to maintaining basal levels of PGE₂, the gastroprotective effect of the pre-treatment with 3α-OH MDA (70%), DLG (81%), and their combination (72%) which was accompanied by significant decreases in leukocyte recruitment, as well as decreases in TNF-α and LTB₄ gastric levels (p < 0.05). We also found that the pre-treatment maintains the basal antioxidant enzyme activities (SOD) and gastric NO and H₂S production even in the presence of indomethacin (p < 0.05). In conclusion, when 3α-OH MDA-DLG is given at a 1:1 combination ratio, the gastroprotective effect and the inflammatory, antioxidant, and gaso-modulation properties are not different from those of treatments using the maximum doses of each compound, revealing that this combination produces promising results for the treatment of gastric ulcers.

The role of hydrogen sulfide in gastrointestinal tract functioning (review)

Despite a fairly large amount of literature data about the involvement of hydrogen sulfide in physiological and pathophysiological processes, its role in gastrointestinal tract functioning has not been studied sufficiently. This review systematizes and generalizes the mechanisms of H2S-associated regulation of gastrointestinal secretion and motility on the basis of literature sources processing and own research results. We analysed world professional literature and sources in Google Scholar, PubMed, MedLine, Embase, Cochrane, and data from more than 50 articles and books on the problem were processed in the article. This review gives a synopsis of the H2S function in the regulation of the secretory and motor-evacuation function, and in stimulating the reparative properties of the digestive tract, and indicates the main mechanisms.

Emerging pharmacological tools to control hydrogen sulfide signaling in critical illness

Hydrogen sulfide (H2S) has long been known as a toxic environmental hazard. Discovery of physiological roles of H2S as a neurotransmitter by Kimura and colleagues triggered an intensive research in the biological roles of H2S in the past decades. Manipulation of H2S levels by inhibiting H2S synthesis or administration of H2S-releasing molecules revealed beneficial as well as harmful effects of H2S. As a result, it is now established that H2S levels are tightly controlled and too much or too little H2S levels cause harm. Nonetheless, translation of sulfide-based therapy to clinical practice has been stymied due to the very low therapeutic index of sulfide and the incomplete understanding of endogenous sulfide metabolism. One potential strategy to circumvent this problem is to use a safe and stable sulfide metabolite that may mediate effects of H2S. Alternatively, endogenous sulfide levels may be controlled using specific sulfide scavengers. In this review article, the role of endogenous H2S production and catabolism will be briefly reviewed followed by an introduction of thiosulfate and H2S scavengers as novel pharmacological tools to control H2S-dependent signaling.

Evaluation of H2S-producing enzymes in cerebrospinal fluid and its relationship with interleukin-6 and neurologic deficits in subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Recent studies have suggested that H₂S may be involved in the pathophysiology of subarachnoid hemorrhage (SAH). Endogenous H₂S is mainly formed by cystathionine β-synthase (CBS), d-amino-acid oxidase (DAO), and 3-mercaptopyruvate sulfotransferase (3-MST) from the substrate cysteine in the central nervous system. In this study, we assessed the expression of CBS, 3-MST, and DAO in cerebrospinal fluid (CSF) from patients with SAH and rats and the expression in the rat brain.

METHODS

CSF samples were collected within 48 h of aneurysm rupture in SAH patients. The CBS, DAO and 3-MST levels in CSF were measured using Western blot analyses, and correlations with the inflammatory parameter Interleukin-6 (IL-6) were assessed. Six months after SAH, the clinical outcomes were assessed.

RESULTS

In human CSF samples, the CBS and DAO protein levels were detected and increased after SAH. However, 3-MST was not detected in the control group CSF but increased after SAH. Strong correlations were observed between the increasing levels of CBS, DAO, and 3-MST and IL-6 2 days after SAH. Furthermore, high CBS, 3-MST and DAO levels in the CSF samples were correlated with poor outcomes at 6 months after SAH onset. We also found that the expression of CBS, DAO and 3-MST in the rat CSF and brain (parietal cortex and hippocampus) increased following SAH. We detected strong correlations between the increases in CBS, 3-MST and IL-6 in the rat CSF and brain samples.

CONCLUSIONS

These results indicate that the upregulated expression of CBS, DAO and 3-MST after SAH was closely associated with the inflammatory response and neurological deficits after SAH.

Rational Design of Specific Recognition Molecules for Simultaneously Monitoring of Endogenous Polysulfide and Hydrogen Sulfide in the Mouse Brain

A biosensor was created for the simultaneous monitoring of endogenous H₂ S_n and H₂ S in mouse brains and exploring their roles in activation of the TRPA1 channel under two types of brain disease models: ischemia and Alzheimer's disease (AD). Based on DFT calculations and electrochemical measurements, two probes, 3,4-bis((2-fluoro-5-nitrobenzoyl)oxy)-benzoic acid (M_PS-1 ) and N-(4-(2,5-dinitrophenoxy) phenyl)-5-(1, 2-dithiolan-3-yl)pentanamide (M_HS-1 ), were synthesized for specific recognition of H₂ S_n and H₂ S. Through co-assembly of the two probes at the mesoporous gold film with good anti-biofouling ability and electrocatalytic activity, this microsensor showed high selectivity for H₂ S_n and H₂ S against potential biological interferences. The biosensor can simultaneously determine the concentration of H₂ S_n from 0.2 to 50 μm, as well as that of H₂ S from 0.2 to 40 μm. The expression of TRPA1 protein positively correlated with levels of H₂ S_n under both ischemia and AD.

Effects of altered maternal folate and vitamin B12 on neurobehavioral outcomes in F1 male mice

Maternal folate and vitamin B₁₂ status during pregnancy may influence development of central nervous system (CNS) in the offspring. Very little attention has been paid to understand the combined effects of both the vitamins during pregnancy. The present study was designed to evaluate the biochemical and behavioral outcomes following alterations in folate and vitamin B₁₂ levels in C57BL/6 mice. The female mice were fed with different combinations of folate and vitamin B₁₂ whereas; males were fed with normal diet for 4 weeks. The mice were mated and the pregnant mice received the same diets as before pregnancy. The F1 male mice were further continued on maternal diet for 6 weeks following neurobehavioral and biochemical assessment. The body weight of the F1 male mice was significantly decreased in the mice that received folate and vitamin B₁₂ deficient diet. Altered cognitive functions were observed in the folate and B₁₂ deficient F1 male mice as assessed by Morris water maze and novel object recognition tests. Spontaneous locomotor activity was decreased in F1 male mice fed with folate and B₁₂ deficient diets. Elevated homocysteine levels and decreased hydrogen sulfide levels were also observed in the brain of F1 male mice on folate and B₁₂ deficient diets. However, GSH and GSSG levels were increased in the brain of the animals supplemented with folate deficient diet with different combinations of B₁₂. The study suggests that exposure of female mice to folate and vitamin B₁₂ deficiency during pregnancy effects in-utero development of fetus, which further leads to behavioral anomalies in adult life and is sufficient to cause impaired cognitive behavior in the subsequent generation. Thus, elucidating the role and importance of maternal dietary folate and B₁₂ ratio during pregnancy.

Data-Driven Identification of Hydrogen Sulfide Scavengers

Hydrogen sulfide (H₂ S) is an important signaling molecule whose up- and down-regulation have specific biological consequences. Although significant advances in H₂ S up-regulation, by the development of H₂ S donors, have been achieved in recent years, precise H₂ S down-regulation is still challenging. The lack of potent/specific inhibitors for H₂ S-producing enzymes contributes to this problem. We expect the development of H₂ S scavengers is an alternative approach to address this problem. Since chemical sensors and scavengers of H₂ S share the same criteria, we constructed a H₂ S sensor database, which summarizes key parameters of reported sensors. Data-driven analysis led to the selection of 30 potential compounds. Further evaluation of these compounds identified a group of promising scavengers, based on the sulfonyl azide template. The efficiency of these scavengers in in vitro and in vivo experiments was demonstrated.

Preconditioning with hydrogen sulfide ameliorates cerebral ischemia/reperfusion injury in a mouse model of transient middle cerebral artery occlusion

Ischemic stroke and reperfusion injury are a common and serve medical situation in the elderly population. H₂S is a gas neuromodulator which also possesses anti-oxidant and anti-inflammatory properties, and is found to play neuroprotective effect in neurodegenerative diseases. This study investigated the effect of endogenous and exogenous H₂S in a mouse model of ischemic stroke. 129P2-Cbs^tm1Unc/J mice with heterozygous mutants in H₂S generating enzyme cystathionine β-synthase were used to study the effect of endogenous H₂S. H₂S donor NaHS was used as exogenous H₂S. Animals were pretreated with H₂S and then subjected to middle cerebral artery occlusion surgery. Behavioral outcome was evaluated by novel object recognition test. Inflammatory cytokines were measured using ELISA. Western blot was used to detect the activation of NF-κB. Aged 129P2-Cbs^tm1Unc/J mice showed exaggerated inflammation and more severe cognitive impairment after ischemia, while exogenous H₂S treatment inhibited inflammation and attenuated behavioral impairment. The anti-inflammatory effect of H₂S was mediated by inhibiting NF-κB. Our findings suggest that both endogenous and exogenous H₂S are involved in the neuroprotection against ischemia/reperfusion-induced cerebral injury.

H2S-based therapies for ischaemic stroke: opportunities and challenges

Stroke is a cerebrovascular disease displaying high mortality and morbidity. Despite extensive efforts, only very few therapies are available for stroke patients as yet. Hydrogen sulfide (H₂S) is thought to be a signalling molecule that is endogenously produced and plays functional roles in the central nervous system. Currently, numerous studies show that H₂S impacts stroke outcomes in animal and cellular models. Here, we review the recent research regarding the effects of endogenously produced H₂S as well as exogenous H₂S donors on stroke pathology, focusing on the potential of H₂S-based therapies in treating ischaemic stroke. We also discuss the several issues that hinder the clinical translation of H₂S-based therapies from the bench. Taken together, we think that H₂S-based therapies are promising strategies for treating cerebral ischaemia if we successfully address these issues.

Hydrogen inhalation protects hypoxic-ischemic brain damage by attenuating inflammation and apoptosis in neonatal rats

Hypoxic–ischemic brain damage (HIBD) is one of the leading causes of brain injury in infant with high risk of mortality and disability; therefore, it is important to explore more feasible and effective treatment strategies. Here, we assessed the neuroprotective effects of different hydrogen inhalation times for the treatment of HIBD. We induced hypoxia–ischemia in Sprague–Dawley rats (postnatal day 7, both sexes), followed by treatment with hydrogen inhalation for 30, 60, or 90 min. Morphological brain injury was assessed by Nissl and TUNEL staining. Acute inflammation was evaluated by examining the expression of interleukin-1β (IL-1β) and NF-κB p65, as well as Iba-1 immunofluorescence in the brain. Neural apoptosis was evaluated by examining the expression of P-JNK and p53 as well as NeuN immunofluorescence. Neurobehavioral function of rats was evaluated by Morris water maze test at 36 days after surgery. The results showed that hypoxia–ischemia injury induced the inflammatory response of microglia; however, these changes were inhibited by hydrogen inhalation. The inhibitory effects became more apparent as the treatment duration increased ( P < 0.05). Furthermore, hypoxia–ischemia induced neuronal damage and increased the expression of the apoptotic factors, P-JNK, and p53, which were attenuated by hydrogen inhalation ( P < 0.05). Hypoxia–ischemia caused long-term spatial memory deficits during brain maturation, which were ameliorated by hydrogen inhalation ( P < 0.01). In conclusion, hypoxia–ischemia induced severe long-term damage to the brain, which could be alleviated by hydrogen inhalation in a time-dependent manner.

Impact statement

Oxidative stress is known to be involved in the main pathological progression of neonatal hypoxic–ischemic brain damage (HIBD). Hydrogen (H2) is an antioxidant that can be used to treat HIBD; however, the mechanism by which hydrogen may be used as a promising treatment for neonates with HIBD is not very clear. This study demonstrated that inhaled H2 is neuroprotective against HIBD in SpragueDawley rats by inhibiting the brain’s inflammatory response and neuronal apoptosis or damage and protecting against spatial memory decline. Further, this study showed that inhaled H2 has potential as a therapeutic approach for HIBD. This is relevant to clinical treatment protocols when hypoxia–ischemia is suspected in neonates.

Breathing hydrogen sulfide prevents delayed paraplegia in mice

Delayed paraplegia complicates the recovery from spinal cord ischemia or traumatic spinal cord injury. While delayed motor neuron apoptosis is implicated in the pathogenesis, no effective treatment or preventive measures is available for delayed paraplegia. Hydrogen sulfide exerts anti-apoptotic effects. Here, we examined effects of hydrogen sulfide breathing on the recovery from transient spinal cord ischemia. Breathing hydrogen sulfide starting 23 h after reperfusion for 5 h prevented delayed paraplegia after 5 min of spinal cord ischemia. Beneficial effects of hydrogen sulfide were mediated by upregulation of anti-apoptotic Bcl-XL and abolished by nitric oxide synthase 2 deficiency. S-nitrosylation of NFkB p65 subunit, which is induced by nitric oxide derived from nitric oxide synthase 2, facilitated subsequent sulfide-induced persulfidation of p65 and transcription of anti-apoptotic genes. These results uncover the molecular mechanism of the anti-apoptotic effects of sulfide based on the interaction between nitric oxide and sulfide. Exploitation of the anti-apoptotic effects of delayed hydrogen sulfide breathing may provide a new therapeutic approach for delayed paraplegia.

Dietary methionine restriction ameliorates the impairment of learning and memory function induced by obesity in mice

Dietary methionine restriction improves impairment of learning and memory function induced by obesity, likely by increasing H₂S production.

The H₂S Donor GYY4137 Stimulates Reactive Oxygen Species Generation in BV2 Cells While Suppressing the Secretion of TNF and Nitric Oxide

GYY4137 is a hydrogen sulfide (H₂S) donor that has been shown to act in an anti-inflammatory manner in vitro and in vivo. Microglial cells are among the major players in immunoinflammatory, degenerative, and neoplastic disorders of the central nervous system, including multiple sclerosis, Parkinson’s disease, Alzheimer’s disease, and glioblastoma multiforme. So far, the effects of GYY4137 on microglial cells have not been thoroughly investigated. In this study, BV2 microglial cells were stimulated with interferon-gamma and lipopolysaccharide and treated with GYY4137. The agent did not influence the viability of BV2 cells in concentrations up to 200 μM. It inhibited tumor necrosis factor but not interleukin-6 production. Expression of CD40 and CD86 were reduced under the influence of the donor. The phagocytic ability of BV2 cells and nitric oxide production were also affected by the agent. Surprisingly, GYY4137 upregulated generation of reactive oxygen species (ROS) by BV2 cells. The effect was mimicked by another H₂S donor, Na₂S, and it was not reproduced in macrophages. Our results demonstrate that GYY4137 downregulates inflammatory properties of BV2 cells but increases their ability to generate ROS. Further investigation of this unexpected phenomenon is warranted.

8e Protects against Acute Cerebral Ischemia by Inhibition of PI3Kγ-Mediated Superoxide Generation in Microglia

The inflammatory response mediated by microglia plays a critical role in the progression of ischemic stroke. Phosphoinositide 3-kinase gamma (PI3Kγ) has been implicated in multiple inflammatory and autoimmune diseases, making it a promising target for therapeutic intervention. The aim of this study was to evaluate the efficacy of 8e, a hydrogen sulfide (H₂S) releasing derivative of 3-n-butylphthalide (NBP), on brain damage and PI3Kγ signaling following cerebral ischemia injury. 8e significantly reduced sensorimotor deficits, focal infarction, brain edema and neural apoptosis at 72 h after transient middle cerebral artery occlusion (tMCAO). The NOX2 isoform of the NADPH oxidase family is considered a major enzymatic source of superoxide. We found that the release of superoxide, together with the expression of NOX2 subunits p47^phox, p-p47^phox, and the upstream PI3Kγ/AKT signaling were all down-regulated by 8e, both in the penumbral region of the rat brain and in the primary cultured microglia subjected to oxygen-glucose deprivation (OGD). With the use of siRNA and pharmacological inhibitors, we further demonstrated that 8e regulates the formation of superoxide in activated microglia through the PI3Kγ/AKT/NOX2 signaling pathway and subsequently prevents neuronal death in neighboring neurons. Our experimental data indicate that 8e is a potential candidate for the treatment of ischemic stroke and PI3Kγ-mediated neuroinflammation.