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

Overexpression of USP35 enhances the protective effect of hUC-MSCs and their extracellular vesicles in oxygen-glucose deprivation/reperfusion-induced SH-SY5Y cells via stabilizing FUNDC1

Ischemia-reperfusion (IR) injury is associated with neurological disorders such as stroke. The therapeutic potential of human umbilical cord mesenchymal stem cells (hUC-MSCs) and their secreted extracellular vesicles (EVs) in alleviating IR injury across various cell types including neuronal cells has been documented. However, the underlying mechanisms through which hUC-MSCs and hUC-MSC-EVs protect neuronal cells from IR-triggered damage are not well understood. In this study, we co-cultured SH-SY5Y neuroblastoma cells with hUC-MSCs or hUC-MSC-EVs and subjected them to oxygen-glucose deprivation/reperfusion (OGD/R) treatment. Our findings indicate that both hUC-MSCs and hUC-MSC-EVs significantly improved viability, reduced apoptosis, promoted autophagy of OGD/R-induced SH-SY5Y cells, and decreased mitochondrial reactive oxygen species levels within them. Furthermore, the neuroprotective effect of hUC-MSCs and hUC-MSC-EVs in OGD/R-induced SH-SY5Y cells was enhanced by overexpressing USP35, a deubiquitinase. Mechanistically, USP35 interacted with and stabilized FUNDC1, a positive regulator of mitochondrial metabolism. Knockdown of FUNDC1 in USP35-overexpressing hUC-MSCs and their secreted EVs eliminated the augmented neuroprotective function induced by excess USP35. In conclusion, these findings underscore the crucial role of USP35 in enhancing the neuroprotective function of hUC-MSCs and their secreted EVs, achieved through the stabilization of FUNDC1 in OGD/R-induced SH-SY5Y cells.

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.

Strategies for gaseous neuromodulator release in chemical neuroscience: Experimental approaches and translational validation

Gasotransmitters are a group of short-lived gaseous signaling molecules displaying diverse biological functions depending upon their localized concentration. Nitric oxide (NO), hydrogen sulfide (H2S), and carbon monoxide (CO) are three important examples of endogenously produced gasotransmitters that play a crucial role in human neurophysiology and pathogenesis. Alterations in their optimal physiological concentrations can lead to various severe pathophysiological consequences, including neurological disorders. Exogenous administration of gasotransmitters has emerged as a prominent therapeutic approach for treating such neurological diseases. However, their gaseous nature and short half-life limit their therapeutic delivery. Therefore, developing synthetic gasotransmitter-releasing strategies having control over the release and duration of these gaseous molecules has become imperative. However, the complex chemistry of synthesis and the challenges of specific quantified delivery of these gases, make their therapeutic application a challenging task. This review article provides a focused overview of emerging strategies for delivering gasotransmitters in a controlled and sustained manner to re-establish neurophysiological homeostasis.

Scutellarin attenuates oxidative stress and neuroinflammation in cerebral ischemia/reperfusion injury through PI3K/Akt-mediated Nrf2 signaling pathways

Cerebral ischemia/reperfusion injury (CIRI) seriously threatens human life and health. Scutellarin (Scu) exhibits neuroprotective effects, but little is known about its underlying mechanism. Therefore, we explored its protective effect on CIRI and the underlying mechanism. Our results demonstrated that Scu rescued HT22 cells from cytotoxicity induced by oxygen and glucose deprivation/reoxygenation (OGD/R). Scu also showed antioxidant activity by promoting nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear translocation, upregulating heme oxygenase-1 (HO-1) expression, increasing superoxide dismutase (SOD) activity, and inhibiting reactive oxygen species (ROS) generation in vitro. Additionally, Scu reduced nuclear factor-kappa B (NF-κB) activity and the levels of pro-inflammatory factors. Interestingly, these effects were abolished by Nrf2 inhibition. Furthermore, Scu reduced infarct volume and blood-brain barrier (BBB) permeability, improved sensorimotor functions and depressive behaviors, and alleviated oxidative stress and neuroinflammation in rats subjected to middle cerebral artery occlusion/reperfusion (MCAO/R). Mechanistically, Scu-induced Nrf2 nuclear accumulation and inactivation of NF-κB were accompanied by an enhanced level of phosphorylated protein kinase B (p-AKT) both in vitro and in vivo. Pharmacologically inhibiting the phosphatidylinositol-3-kinase/protein kinase B (PI3K/AKT) pathway blocked Scu-induced Nrf2 nuclear translocation and inactivation of NF-κB, as well as its antioxidant and anti-inflammatory activities. In summary, these results suggest that Scu exhibits antioxidant, anti-inflammatory, and neuroprotective effects in CIRI through Nrf2 activation mediated by the PI3K/Akt pathway.

Neuronal Responses to Ischemia: Scoping Review of Insights from Human-Derived In Vitro Models

Translation of neuroprotective treatment effects from experimental animal models to patients with cerebral ischemia has been challenging. Since pathophysiological processes may vary across species, an experimental model to clarify human-specific neuronal pathomechanisms may help. We conducted a scoping review of the literature on human neuronal in vitro models that have been used to study neuronal responses to ischemia or hypoxia, the parts of the pathophysiological cascade that have been investigated in those models, and evidence on effects of interventions. We included 147 studies on four different human neuronal models. The majority of the studies (132/147) was conducted in SH-SY5Y cells, which is a cancerous cell line derived from a single neuroblastoma patient. Of these, 119/132 used undifferentiated SH-SY5Y cells, that lack many neuronal characteristics. Two studies used healthy human induced pluripotent stem cell derived neuronal networks. Most studies used microscopic measures and established hypoxia induced cell death, oxidative stress, or inflammation. Only one study investigated the effect of hypoxia on neuronal network functionality using micro-electrode arrays. Treatment targets included oxidative stress, inflammation, cell death, and neuronal network stimulation. We discuss (dis)advantages of the various model systems and propose future perspectives for research into human neuronal responses to ischemia or hypoxia.

ADT-OH improves intestinal barrier function and remodels the gut microbiota in DSS-induced colitis

Owing to the increasing incidence and prevalence of inflammatory bowel disease (IBD) worldwide, effective and safe treatments for IBD are urgently needed. Hydrogen sulfide (H2S) is an endogenous gasotransmitter and plays an important role in inflammation. To date, H2S-releasing agents are viewed as potential anti-inflammatory drugs. The slow-releasing H2S donor 5-(4-hydroxyphenyl)-3H-1,2-dithiole-3-thione (ADT-OH), known as a potent therapeutic with chemopreventive and cytoprotective properties, has received attention recently. Here, we reported its anti-inflammatory effects on dextran sodium sulfate (DSS)-induced acute (7 days) and chronic (30 days) colitis. We found that ADT-OH effectively reduced the DSS-colitis clinical score and reversed the inflammation-induced shortening of colon length. Moreover, ADT-OH reduced intestinal inflammation by suppressing the nuclear factor kappa-B pathway. In vivo and in vitro results showed that ADT-OH decreased intestinal permeability by increasing the expression of zonula occludens-1 and occludin and blocking increases in myosin II regulatory light chain phosphorylation and epithelial myosin light chain kinase protein expression levels. In addition, ADT-OH restored intestinal microbiota dysbiosis characterized by the significantly increased abundance of Muribaculaceae and Alistipes and markedly decreased abundance of Helicobacter, Mucispirillum, Parasutterella, and Desulfovibrio. Transplanting ADT-OH-modulated microbiota can alleviate DSS-induced colitis and negatively regulate the expression of local and systemic proinflammatory cytokines. Collectively, ADT-OH is safe without any short-term (5 days) or long-term (30 days) toxicological adverse effects and can be used as an alternative therapeutic agent for IBD treatment.

Hydrogen sulfide: Recent development of its dual donors and hybrid drugs

Hydrogen sulfide (H2 S) is an important gaseous signalling molecule known to be critically involved in regulating cellular redox homeostasis. As the beneficial and therapeutic effects of H2 S in pathophysiology, such as in cardiovascular and neurodegenerative diseases, have emerged, so too has the drive for the development of H2 S-releasing compounds (aka donors) and their therapeutic applications. Most reported donor compounds singularly release H2 S through biocompatible triggers. An emerging area in the field is the development of compounds that can co-deliver H2 S with other drugs or biologically relevant species, such as reactive oxygen and nitrogen species (ROS and RNS, respectively). These H2 S-based dual donors and hybrid drugs are expected to offset negative side effects from individual treatments or achieve synergistic effects rendering them more clinically effective. Additionally, considering that molecules exist and interact physiologically, dual donors may more accurately mimic biological systems as compared to single donors and allow for the elucidation of fundamental chemistry and biology. This review focuses on the recent advances in the development of H2 S-based dual donors and hybrid drugs along with their design principles and synergistic effects.

Neuroprotection of NAD+ and NBP against ischemia/reperfusion brain injury is associated with restoration of sirtuin-regulated metabolic homeostasis

Background: Ischemic stroke seriously threatens human health because of high rates of morbidity, mortality and disability. This study compared the effects of nicotinamide adenine dinucleotide (NAD+) and butylphthalide (NBP) on in vitro and in vivo ischemic stroke models.

Methods: Transient middle cerebral artery occlusion/reperfusion (t-MCAO/R) model was established in mice, and the cultured primary cortical neurons were subjected to oxygen-glucose deprivation/reoxygenation (OGD/R). Cerebral infarct volume, neurobehavioral indices, antioxidant activity, ATP level and lactic acid content were determined. The neuroprotective effects of NAD+ or NBP were compared using sirtuin inhibitor niacinamide (NAM).

Results: Intraperitoneal injection of NBP within 4 h or intravenous injection of NAD+ within 1 h after t-MCAO/R significantly reduced the volume of infarcts, cerebral edema, and neurological deficits. Administration of NAD+ and NBP immediately after t-MCAO/R in mice showed similar neuroprotection against acute and long-term ischemic injury. Both NAD+ and NBP significantly inhibited the accumulation of MDA and H2O2 and reduced oxidative stress. NAD+ was superior to NBP in inhibiting lipid oxidation and DNA damage. Furthermore, although both NAD+ and NBP improved the morphology of mitochondrial damage induced by ischemia/reperfusion, NAD+ more effectively reversed the decrease of ATP and increase of lactic acid after ischemia/reperfusion compared with NBP. NAD+ but not NBP treatment significantly upregulated SIRT3 in the brain, but the sirtuin inhibitor NAM could abolish the protective effect of NAD+ and NBP by inhibiting SIRT1 or SIRT3.

Conclusions: These results confirmed the protective effects of NAD+ and NBP on cerebral ischemic injury. NBP and NAD+ showed similar antioxidant effects, while NAD+ had better ability in restoring energy metabolism, possibly through upregulating the activity of SIRT1 and SIRT3. The protection provided by NBP against cerebral ischemia/reperfusion may be achieved through SIRT1.

Intranasal administration of polysulfide prevents neurodegeneration in spinal cord and rescues mice from delayed paraplegia after spinal cord ischemia

BACKGROUND

Delayed paraplegia is a devastating complication of thoracoabdominal aortic surgery. Hydrogen sulfide (H₂S) was reported to be protective in a mouse model of spinal cord ischemia and the beneficial effect of H₂S has been attributed to polysulfides. The objective of this study was to investigate the effects of polysulfides on delayed paraplegia after spinal cord ischemia.

METHODS AND RESULTS

Spinal cord ischemia was induced in male and female C57BL/6J mice by clamping the aortic arch and the left subclavian artery. Glutathione trisulfide (GSSSG), glutathione (GSH), glutathione disulfide (GSSG), or vehicle alone was administered intranasally at 0, 8, 23, and 32 h after surgery. All mice treated with vehicle alone developed paraplegia within 48 h after surgery. GSSSG, but not GSH or GSSG, prevented paraplegia in 8 of 11 male mice (73%) and 6 of 8 female mice (75%). Intranasal administration of ³⁴S-labeled GSSSG rapidly increased ³⁴S-labeled sulfane sulfur species in the lumbar spinal cord. In mice treated with intranasal GSSSG, there were increased sulfane sulfur levels, and decreased neurodegeneration, microglia activation, and caspase-3 activation in the lumbar spinal cord. In vitro studies using murine primary cortical neurons showed that GSSSG increased intracellular levels of sulfane sulfur. GSSSG, but not GSH or GSSG, dose-dependently improved cell viability after oxygen and glucose deprivation/reoxygenation (OGD/R). Pantethine trisulfide (PTN-SSS) also increased intracellular sulfane sulfur and improved cell viability after OGD/R. Intranasal administration of PTN-SSS, but not pantethine, prevented paraplegia in 6 of 9 male mice (66%).

CONCLUSIONS

Intranasal administration of polysulfides rescued mice from delayed paraplegia after transient spinal cord ischemia. The neuroprotective effects of GSSSG were associated with increased levels of polysulfides and sulfane sulfur in the lumbar spinal cord. Targeted delivery of sulfane sulfur by polysulfides may prove to be a novel approach to the treatment of neurodegenerative diseases.

Synthesis and neuroprotective effects of H2S-donor-peptide hybrids on hippocampal neuronal cells

Hydrogen sulfide (H₂S) has emerged as an endogenous signaling molecule that functions in many physiological and pathological processes of human cells in health and disease, including neuromodulation and neuroprotection, inflammation, angiogenesis, and vasorelaxation. The limited clinical applications of current H₂S donors have led to the development of H₂S donor hybrid compounds that combine current H₂S donors with bioactive molecules. Finely tuned multi-targeting hybrid molecules have been shown to have complementary neuroprotective effects against reactive oxygen species (ROS)-induced oxidative stress. In this study, we developed hybrid molecules combining a dithiolethione-based slow-releasing H₂S donor that exerts neuroprotective effects, with the tripeptides glycyl-L-histidyl-l-lysine (GHK) and L-alanyl-L-cystinyl-l-glutamine (ACQ), two natural products that exhibit powerful antioxidant effects. In particular, a hybrid combination of a dithiolethione-based slow-releasing H₂S donor and ACQ exhibited significant neuroprotective effects against glutamate-induced oxidative damage in HT22 hippocampal neuronal cells. This hybrid remarkably suppressed Ca²⁺ accumulation and ROS production. Furthermore, it efficiently inhibited apoptotic neuronal cell death by blocking apoptosis-inducing factor release and its translocation to the nucleus. These results indicate that the hybrid efficiently inhibited apoptotic neuronal cell damage by complementary neuroprotective actions.

Oral Administration of Glutathione Trisulfide Increases Reactive Sulfur Levels in Dorsal Root Ganglion and Ameliorates Paclitaxel-Induced Peripheral Neuropathy in Mice

Peripheral neuropathy is a dose-limiting side effect of chemotherapy with paclitaxel. Paclitaxel-induced peripheral neuropathy (PIPN) is typically characterized by a predominantly sensory neuropathy presenting with allodynia, hyperalgesia and spontaneous pain. Oxidative mitochondrial damage in peripheral sensory neurons is implicated in the pathogenesis of PIPN. Reactive sulfur species, including persulfides (RSSH) and polysulfides (RSnH), are strong nucleophilic and electrophilic compounds that exert antioxidant effects and protect mitochondria. Here, we examined the potential neuroprotective effects of glutathione trisulfide (GSSSG) in a mouse model of PIPN. Intraperitoneal administration of paclitaxel at 4 mg/kg/day for 4 days induced mechanical allodynia and thermal hyperalgesia in mice. Oral administration of GSSSG at 50 mg/kg/day for 28 days ameliorated mechanical allodynia, but not thermal hyperalgesia. Two hours after oral administration, 34S-labeled GSSSG was detected in lumber dorsal root ganglia (DRG) and in the lumber spinal cord. In mice treated with paclitaxel, GSSSG upregulated expression of genes encoding antioxidant proteins in lumber DRG, prevented loss of unmyelinated axons and inhibited degeneration of mitochondria in the sciatic nerve. In cultured primary neurons from cortex and DRG, GSSSG mitigated paclitaxel-induced superoxide production, loss of axonal mitochondria, and axonal degeneration. These results indicate that oral administration of GSSSG mitigates PIPN by preventing axonal degeneration and mitochondria damage in peripheral sensory nerves. The findings suggest that administration of GSSSG may be an approach to the treatment or prevention of PIPN and other peripheral neuropathies.

Optimization of clofibrate with O-desmethyl anetholtrithione lead to a novel hypolipidemia compound with hepatoprotective effect

Oxidative stress and inflammation were considered to be the major mechanisms in liver damage caused by clofibrate (CF). In order to obtain lipid-lowering drugs with less liver damage, the structure of clofibrate was optimized by O-desmethyl anetholtrithione and got the target compound clofibrate-O-desmethyl anetholtrithione (CF-ATT). CF-ATT significantly reduced the levels of plasma triglycerides (TG), total cholesterol (TC) in hyperlipidemia mice induced by Triton WR-1339. In addition, CF-ATT has a significantly protective effect on the liver compared with CF. The liver weight and liver coefficient were reduced. The hepatic function indexes were also decreased, such as aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP). Histopathological examination of the liver revealed that inflammatory cell infiltration, nuclear degeneration, cytoplasmic loosening and hepatocyte necrosis were ameliorated by administration with CF-ATT. The hepatoprotective mechanism showed that CF-ATT significantly up-regulated Nrf2 and HO-1 protein expression and down-regulated p-NF-κB P65 expression in the liver. CF-ATT has obviously antioxidant and anti-inflammatory activity. These findings suggested that CF-ATT has significant hypolipidemia activity and exact hepatoprotective effect possibly through the Nrf2/NF-κB-mediated signal pathway.

NADPH is superior to NADH or edaravone in ameliorating metabolic disturbance and brain injury in ischemic stroke

Our previous studies confirm that exogenous reduced nicotinamide adenine dinucleotide phosphate (NADPH) exerts a neuroprotective effect in animal models of ischemic stroke, and its primary mechanism is related to anti-oxidative stress and improved energy metabolism. However, it is unknown whether nicotinamide adenine dinucleotide (NADH) also plays a neuroprotective role and whether NADPH is superior to NADH against ischemic stroke? In this study we compared the efficacy of NADH, NADPH, and edaravone in ameliorating brain injury and metabolic stress in ischemic stroke. Transient middle cerebral artery occlusion/reperfusion (t-MCAO/R) mouse model and in vitro oxygen glucose deprivation/reoxygenation (OGD/R) model were established. The mice were intravenously administered the optimal dose of NADPH (7.5 mg/kg), NADH (22.5 mg/kg), or edaravone (3 mg/kg) immediately after reperfusion. We showed that the overall efficacy of NADPH in ameliorating ischemic injury was superior to NADH and edaravone. NADPH had a longer therapeutic time window (within 5 h) after reperfusion than NADH and edaravone (within 2 h) for ischemic stroke. In addition, NADPH and edaravone were better in alleviating the brain atrophy, while NADH and NADPH were better in increasing the long-term survival rate. NADPH showed stronger antioxidant effects than NADH and edaravone; but NADH was the best in terms of maintaining energy metabolism. Taken together, this study demonstrates that NADPH exerts better neuroprotective effects against ischemic stroke than NADH and edaravone.

Inhalational Gases for Neuroprotection in Traumatic Brain Injury

Despite multiple prior pharmacological trials in traumatic brain injury (TBI), the search for an effective, safe, and practical treatment of these patients remains ongoing. Given the ease of delivery and rapid absorption into the systemic circulation, inhalational gases that have neuroprotective properties will be an invaluable resource in the clinical management of TBI patients. In this review, we perform a systematic review of both pre-clinical and clinical reports describing inhalational gas therapy in the setting of TBI. Hyperbaric oxygen, which has been investigated for many years, and some of the newest developments are reviewed. Also, promising new therapies such as hydrogen gas, hydrogen sulfide gas, and nitric oxide are discussed. Moreover, novel therapies such as xenon and argon gases and delivery methods using microbubbles are explored.

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.

Role of Hydrogen Sulfide in Myocardial Ischemia-Reperfusion Injury

ABSTRACT

Hydrogen sulfide (H2S), generally known as a new gas signal molecule after nitric oxide and carbon monoxide, has been found as an important endogenous gasotransmitter in the last few decades, and it plays a significant role in the cardiovascular system both pathologically and physiologically. In recent years, there is growing evidence that H2S provides myocardial protection against myocardial ischemia-reperfusion injury (MIRI), which resulted in an ongoing focus on the possible mechanisms of action accounting for the H2S cardioprotective effect. At present, lots of mechanisms of action have been verified through in vitro and in vivo models of I/R injury, such as S-sulfhydrated modification, antiapoptosis, effects on microRNA, bidirectional effect on autophagy, antioxidant stress, or interaction with NO and CO. With advances in understanding of the molecular pathogenesis of MIRI and pharmacology studies, the design, the development, and the pharmacological characterization of H2S donor drugs have made great important progress. This review summarizes the latest research progress on the role of H2S in MIRI, systematically explains the molecular mechanism of H2S affecting MIRI, and provides a new idea for the formulation of a myocardial protection strategy in the future.

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.

Prenatal electronic cigarette exposure decreases brain glucose utilization and worsens outcome in offspring hypoxic-ischemic brain injury

It has been shown that prenatal nicotine and tobacco smoke exposure can cause different neurobehavioral disorders in the offspring. We hypothesize that prenatal exposure to nicotine-containing electronic cigarette (e-Cig) vapor can predispose newborn to enhanced sensitivity to hypoxic-ischemic (HI) brain injury and impaired motor and cognitive functions. In this study, pregnant CD1 mice were exposed to e-Cig vapor (2.4% nicotine). Primary cortical neurons isolated from e-Cig exposed fetus were exposed to oxygen-glucose deprivation followed by reoxygenation (OGD/R) to mimic HI brain injury. Cell viability and glucose utilization were analyzed in these neurons. HI brain injury was induced in 8-9-day-old pups. Short-term brain injury was evaluated by triphenyltetrazolium chloride staining. Long-term motor and cognitive functions were evaluated by open field, novel object recognition, Morris water maze, and foot fault tests. Western blotting and immunofluorescence were done to characterize glucose transporters in offspring brain. We found that e-Cig exposed neurons demonstrated decreased cell viability and glucose utilization in OGD/R. Prenatally e-Cig exposed pups also had increased brain injury and edema 24 hr after HI brain injury. Further, in utero e-Cig exposed offspring with HI brain injury displayed impaired memory, learning, and motor coordination at adolescence. Additionally, the expression of glucose transporters decreased in e-Cig exposed offspring brain after HI brain injury. These results indicate that reduced glucose utilization can contribute to prenatal e-Cig exposure induced worsened HI brain injury in offspring. This study is instrumental in elucidating the possible deleterious effects of e-Cig use in the general population.

Effects of β-HgS on cell viability and intracellular oxidative stress in PC-12 cells

Traditional Tibetan medicines containing β-HgS have been used to treat chronic ailments for thousands of years. The effects were studied of β-HgS on cell viability and intracellular oxidative stress in PC-12 cells.

Organ transcriptomes of the lucinid clam Loripes orbiculatus (Poli, 1791) provide insights into their specialised roles in the biology of a chemosymbiotic bivalve

BACKGROUND

The lucinid clam Loripes orbiculatus lives in a nutritional symbiosis with sulphur-oxidizing bacteria housed in its gills. Although our understanding of the lucinid endosymbiont physiology and metabolism has made significant progress, relatively little is known about how the host regulates the symbiosis at the genetic and molecular levels. We generated transcriptomes from four L. orbiculatus organs (gills, foot, visceral mass, and mantle) for differential expression analyses, to better understand this clam's physiological adaptations to a chemosymbiotic lifestyle, and how it regulates nutritional and immune interactions with its symbionts.

RESULTS

The transcriptome profile of the symbiont-housing gill suggests the regulation of apoptosis and innate immunity are important processes in this organ. We also identified many transcripts encoding ion transporters from the solute carrier family that possibly allow metabolite exchange between host and symbiont. Despite the clam holobiont's clear reliance on chemosynthesis, the clam's visceral mass, which contains the digestive tract, is characterised by enzymes involved in digestion, carbohydrate recognition and metabolism, suggesting that L. orbiculatus has a mixotrophic diet. The foot transcriptome is dominated by the biosynthesis of glycoproteins for the construction of mucus tubes, and receptors that mediate the detection of chemical cues in the environment.

CONCLUSIONS

The transcriptome profiles of gills, mantle, foot and visceral mass provide insights into the molecular basis underlying the functional specialisation of bivalve organs adapted to a chemosymbiotic lifestyle.

Sustained Release of Hydrogen Sulfide (H2S) from Poly(Lactic Acid) Functionalized 4-Hydroxythiobenzamide Microparticles to Protect Against Oxidative Damage

Hydrogen sulfide (H2S) has emerged as a gaseous mediator capable of exhibiting many beneficial properties including cytoprotection, anti-inflammation, and vasodilation. The study presented here provides characterization of a poly(lactic acid) polymer with a functionalized 4-hydroxythiobenzamide (PLA-4HTB) capable of extended H2S release. The polymer was used to fabricate microparticles that can be potentially loaded with a drug allowing for co-release of the drug and H2S. Microparticles with the average diameter of 500 ± 207 nm were fabricated and shown to release 77.0 ± 1.76 µM of H2S over 4 weeks (release of H2S from 1 mg of particles). To test for the antioxidant properties of the PLA-4HTB microparticles, human embryonic kidney 293 cells were first incubated with PLA-4HTB microparticles and then oxidative stress was induced using CoCl2. Particle suspensions of 1 mg/mL were shown to protect cells resulting in reactive oxygen species (ROS) levels of superoxide that were similar to that of the control group. The microparticles fabricated from the PLA-4HTB released H2S over a sustained period of weeks to months, while providing protection from ROS. The microparticles described in this article represent a new platform technology that could be used to prevent and treat diseases caused by oxidative damage.

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.

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.

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.

Nicotine and electronic cigarette (E-Cig) exposure decreases brain glucose utilization in ischemic stroke

Previous studies in our laboratory have shown that nicotine exposure decreases glucose transport across the blood-brain barrier in ischemia-reperfusion conditions. We hypothesize that nicotine can also dysregulate brain parenchymal glucose utilization by altering glucose transporters with effects on sensitivity to ischemic stroke. In this study, we investigated the effects of nicotine exposure on neuronal glucose utilization using an in vitro ischemic stroke model. We also tested the effects of e-Cig vaping on ischemic brain glucose utilization using an acute brain slice technique. Primary cortical neurons and brain slices were subjected to oxygen-glucose deprivation followed by reoxygenation to mimic ischemia-reperfusion injury. We estimated brain cell glucose utilization by measuring the uptake of [3 H] deoxy-d-glucose. Immunofluorescence and western blotting were done to characterize glucose transporters (GLUTs) and α7 nicotinic acetylcholine receptor (nAChR) expression. Furthermore, we used a glycolytic stress test to measure the effects of nicotine exposure on neuronal glucose metabolism. We observed that short- and long-term nicotine/cotinine exposure significantly decreased neuronal glucose utilization in ischemic conditions and the non-specific nAChR antagonist, mecamylamine reversed this effect. Nicotine/cotinine exposure also decreased neuronal GLUT1 and up-regulated α7 nAChR expression and decreased glycolysis. Exposure of mice to e-Cig vapor for 7 days likewise decreases brain glucose uptake under normoxic and ischemic conditions along with down-regulation of GLUT1 and GLUT3 expressions. These data support, from a cerebrovascular perspective, that nicotine and/or e-Cig vaping induce a state of glucose deprivation at the neurovascular unit which could lead to enhanced ischemic brain injury and/or stroke risk. OPEN PRACTICES: Open Science: This manuscript was awarded with the Open Materials Badge. For more information see: https://cos.io/our-services/open-science-badges/.

Role of Nitric Oxide and Hydrogen Sulfide in Ischemic Stroke and the Emergent Epigenetic Underpinnings

Nitric oxide (NO) and hydrogen sulfide (H₂S) are the key gasotransmitters with an imperious role in the maintenance of cerebrovascular homeostasis. A decline in their levels contributes to endothelial dysfunction that portends ischemic stroke (IS) or cerebral ischemia/reperfusion (CI/R). Nevertheless, their exorbitant production during CI/R is associated with exacerbation of cerebrovascular injury in the post-stroke epoch. NO-producing nitric oxide synthases are implicated in IS pathology and their activity is regulated, inter alia, by various post-translational modifications and chromatin-based mechanisms. These account for heterogeneous alterations in NO production in a disease setting like IS. Interestingly, NO per se has been posited as an endogenous epigenetic modulator. Further, there is compelling evidence for an ingenious crosstalk between NO and H₂S in effecting the canonical (direct) and non-canonical (off-target collateral) functions. In this regard, NO-mediated S-nitrosylation and H₂S-mediated S-sulfhydration of specific reactive thiols in an expanding array of target proteins are the principal modalities mediating the all-pervasive influence of NO and H₂S on cell fate in an ischemic brain. An integrated stress response subsuming unfolded protein response and autophagy to cellular stressors like endoplasmic reticulum stress, in part, is entrenched in such signaling modalities that substantiate the role of NO and H₂S in priming the cells for stress response. The precis presented here provides a comprehension on the multifarious actions of NO and H₂S and their epigenetic underpinnings, their crosstalk in maintenance of cerebrovascular homeostasis, and their "Janus bifrons" effect in IS milieu together with plausible therapeutic implications.

Protective Effect of Klotho against Ischemic Brain Injury Is Associated with Inhibition of RIG-I/NF-κB Signaling

Aging is the greatest independent risk factor for the occurrence of stroke and poor outcomes, at least partially through progressive increases in oxidative stress and inflammation with advanced age. Klotho is an antiaging gene, the expression of which declines with age. Klotho may protect against neuronal oxidative damage that is induced by glutamate. The present study investigated the effects of Klotho overexpression and knockdown by an intracerebroventricular injection of a lentiviral vector that encoded murine Klotho (LV-KL) or rat Klotho short-hairpin RNA (LV-KL shRNA) on cerebral ischemia injury and the underlying anti-neuroinflammatory mechanism. The overexpression of Klotho induced by LV-KL significantly improved neurobehavioral deficits and increased the number of live neurons in the hippocampal CA1 and caudate putamen subregions 72 h after cerebral hypoperfusion that was induced by transient bilateral common carotid artery occlusion (2VO) in mice. The overexpression of Klotho significantly decreased the immunoreactivity of glial fibrillary acidic protein and ionized calcium binding adaptor molecule-1, the expression of retinoic-acid-inducible gene-I, the nuclear translocation of nuclear factor-κB, and the production of proinflammatory cytokines (tumor necrosis factor α and interleukin-6) in 2VO mice. The knockdown of Klotho mediated by LV-KL shRNA in the brain exacerbated neurological dysfunction and cerebral infarct after 22 h of reperfusion following 2 h middle cerebral artery occlusion in rats. These findings suggest that Klotho itself or enhancers of Klotho may compensate for its aging-related decline, thus providing a promising therapeutic approach for acute ischemic stroke during advanced age.

Klotho upregulation contributes to the neuroprotection of ligustilide against cerebral ischemic injury in mice

Klotho, an aging-suppressor gene, encodes a protein that potentially acts as a neuroprotective factor. Our previous studies showed that ligustilide minimizes the cognitive dysfunction and brain damage induced by cerebral ischemia; however, the underlying mechanisms remain unclear. This study aims to investigate whether klotho is involved in the protective effects of ligustilide against cerebral ischemic injury in mice. Cerebral ischemia was induced by bilateral common carotid arterial occlusion. Neurobehavioral tests as well as Nissl and Fluoro-Jade B staining were used to evaluate the protective effects of ligustilide in cerebral ischemia, and Western blotting and ELISA approaches were used to investigate the underlying mechanisms. Administration of ligustilide prevented the development of neurological deficits and reduced neuronal loss in the hippocampal CA1 region and the caudate putamen after cerebral ischemia. The protective effects were associated with inhibition of the RIG-I/NF-κB p65 and Akt/FoxO1 pathways and with prevention of inflammation and oxidative stress in the brain. Further, downregulation of klotho could attenuate the neuroprotection of ligustilide against cerebral ischemic injury. Ligustilide exerted neuroprotective effects in mice after cerebral ischemia by regulating anti-inflammatory and anti-oxidant signaling pathways. Furthermore, klotho upregulation contributes to the neuroprotection of LIG against cerebral ischemic injury. These results indicated that ligustilide may be a promising therapeutic agent for the treatment of cerebral ischemia.

Age-Dependent, Subunit Specific Action of Hydrogen Sulfide on GluN1/2A and GluN1/2B NMDA Receptors

Hydrogen sulfide (H₂S) is an endogenously produced neuroactive gas implicated in many key processes in the peripheral and central nervous system. Whereas the neuroprotective role of H₂S has been shown in adult brain, the action of this messenger in newborns remains unclear. One of the known targets of H₂S in the nervous system is the N-methyl-D-aspartate (NMDA) glutamate receptor which can be composed of different subunits with distinct functional properties. In the present study, using patch clamp technique, we compared the effects of the H₂S donor sodium hydrosulfide (NaHS, 100 μM) on hippocampal NMDA receptor mediated currents in rats of the first and third postnatal weeks. This was supplemented by testing effects of NaHS on recombinant GluN1/2A and GluN1/2B NMDA receptors expressed in HEK293T cells. The main finding is that NaHS action on NMDA currents is age-dependent. Currents were reduced in newborns but increased in older juvenile rats. Consistent with an age-dependent switch in NMDA receptor composition, in HEK239T cells expressing GluN1/2A receptors, NaHS increased NMDA activated currents associated with acceleration of desensitization and decrease of the deactivation rate. In contrast, in GluN1/2B NMDA receptors, which are prevalent in newborns, NaHS decreased currents and reduced receptor deactivation without effect on the desensitization rate. Adenylate cyclase inhibitor MDL-12330A (10 μM) did not prevent the age-dependent effects of NaHS on NMDA evoked currents in pyramidal neurons of hippocampus. The reducing agent dithiothreitol (DTT, 2 mM) applied on HEK293T cells prevented facilitation induced by NaHS on GluN1/2A NMDA receptors, however in GluN1/2B NMDA receptors the inhibitory effect of NaHS was still observed. Our data indicate age-dependent effect of H₂S on NMDA receptor mediated currents determined by glutamate receptor subunit composition. While the inhibitory action of H₂ on GluN1/2B receptors could limit the excessive activation in early age, the enhanced functionality of GluN1/2A receptor in the presence of this gasotransmitter can enlarge synaptic efficacy and promote synaptic plasticity in adults.

Combination of NAD+ and NADPH Offers Greater Neuroprotection in Ischemic Stroke Models by Relieving Metabolic Stress

Both reduced nicotinamide adenine dinucleotide phosphate (NADPH) and β-nicotinamide adenine dinucleotide hydrate (NAD⁺) have been reported to have potent neuroprotective effects against ischemic neuronal injury. Both NADPH and NAD⁺ are essential cofactors for anti-oxidation and cellular energy metabolism. We investigated if combined NADPH and NAD⁺ could offer better neuroprotective effects on cellular and animal models of ischemic stroke. In vitro studies with primary cultured neurons demonstrated that NAD⁺ was effective in protecting neurons against oxygen-glucose deprivation/reoxygenation (OGD/R) injury when given during the early time period of reoxygenation. In vivo studies in mice also suggested that NAD⁺ was effective for ameliorating ischemic brain damage when administered within 2 h after reperfusion. The combination of NADPH and NAD⁺ provided not only greater beneficial effects but also larger therapeutic window in both cellular and animal models of stroke. The combination of NADPH and NAD⁺ significantly increased the levels of adenosine triphosphate (ATP) and reduced the levels of reactive oxygen species (ROS) and oxidative damage of macromolecules. Furthermore, the combined medication significantly reduced long-term mortality, improved the functional recovery, and inhibited signaling pathways involved in apoptosis and necroptosis after ischemic stroke. The present study indicates that the combination of NAD⁺ and NADPH can produce greater therapeutic effects with smaller dose of NADPH; on the other hand, NADPH can significantly prolong the therapeutic window of NAD⁺. The current results suggest that the combination of NADPH and NAD⁺ may provide a novel effective therapy for ischemic stroke.

Neuroprotective effects of a novel peptide, FK18, under oxygen-glucose deprivation in SH-SY5Y cells and retinal ischemia in rats via the Akt pathway

Ischemic neuronal injury is associated with several life- and vision-threatening diseases. Neuroprotection is essential in the treatment of these diseases. Here, we identified and characterized a novel peptide, FK18, from basic fibroblast growth factor (bFGF). We further assessed the neuroprotective effects of this peptide and its potential mechanisms using the in vitro oxygen-glucose deprivation (OGD) model in SH-SY5Y cells and the in vivo retinal ischemia-reperfusion (I/R) injury model to mimic ischemic neuronal injury. Our results suggested that FK18 significantly increased the viability of and attenuated the apoptosis of SH-SY5Y cells. It also markedly alleviated I/R-induced retinal neuronal apoptosis, damage to retinal ganglion cells (RGCs), and morphological and functional damage to the retina. Moreover, FK18 increased Akt phosphorylation under both normoxic and OGD conditions, attenuated mitochondrial translocation of the proapoptotic protein Bad, up-regulated the expression of Bcl-2/Bax, and inhibited the release of cytochrome c from the mitochondria into the cytoplasm. These results suggested that FK18 is a novel neuroprotective agent that may serve as a prototype for neuroprotective drug development.

Characterization of the Major Purine and Pyrimidine Adducts Formed after Incubations of 1-Chloro-3-buten-2-one with Single-/Double-Stranded DNA and Human Cells

We have previously shown that 1-chloro-3-buten-2-one (CBO), a potential reactive metabolite of 1,3-butadiene (BD), exhibits potent cytotoxicity and genotoxicity that have been attributed in part to its reactivity toward DNA. In an effort to identify the DNA adducts of CBO, we characterized the CBO reactions with 2'-deoxyguanosine (dG), 2'-deoxycytidine (dC), and 2'-deoxyadenosine (dA) under in vitro physiological conditions (pH 7.4, 37 °C). In the present study, we investigated the CBO reaction with 2'-deoxythymidine (dT) and compared the rate constants of the reactions of CBO with dA, dC, dG, and dT at both individual- and mixed-nucleosides levels. We also investigated the reactions of CBO with single- and double-stranded DNA using HPLC with UV detection after adducts were released by either acid or enzymatic hydrolysis of DNA. Consistent with the results from the nucleoside reactions and the rate constant experiments, 1,N⁶-(1-hydroxy-1-chloromethylpropan-1,3-diyl)adenine (A-2D) was identified as the major DNA adduct detected after acid hydrolysis, followed by N7-(4-chloro-3-oxobutyl)guanine (CG-2H) and a small amount of 1,N⁶-(1-hydroxy-1-hydroxymethylpropan-1,3-diyl)adenine (A-1D). After enzymatic hydrolysis, 1,N⁶-(1-hydroxy-1-hydroxymethylpropan-1,3-diyl)-2'-dexoyadenosine (dA-1), 3,N⁴-(1-hydroxy-1-hydroxymethylpropan-1,3-diyl)-2'-deoxycytidine (dC-1/2), and 1,N²-(3-hydroxy-3-hydroxymethylpropan-1,3-diyl)-2'-dexoyguanosine (CG-1) were detected, with dA-1 being the major product, followed by dC-1/2. When a nontoxic concentration of CBO (1 μM) was incubated with HepG2 cells, no adducts could be detected by LC-MS. However, pretreatment of cells with l-buthionine sulfoximine to deplete GSH levels allowed A-2D to be consistently detected in cellular DNA. These results may contribute to a better understanding of the role of the DNA adducts in CBO genotoxicity and mutagenicity. It also suggests that A-2D could be developed as a biomarker of CBO formation after BD exposure in vivo.

A Novel Danshensu Derivative Prevents Cardiac Dysfunction and Improves the Chemotherapeutic Efficacy of Doxorubicin in Breast Cancer Cells

Doxorubicin (Dox) is an anthracycline antibiotic widely used in clinics as an anticancer agent. However, the use of Dox is limited by its cardiotoxicity. We have previously shown that a Danshensu (DSS) derivative, ADTM, displayed strong cardioprotective effects. With improved chemical stability and activity, a novel DSS derivative, D006, based on the structure of ADTM, was synthesized. In the present study, the protective effects of D006, indexed by attenuation of the cardiotoxicity induced by Dox as well as chemosensitizing effects that increase the antitumor activity of Dox, were investigated. Our results showed that D006 was more potent than either parental compound, or their use in combination, in ameliorating Dox-induced toxicity in H9c2 cells. In our zebrafish model, D006, but not DSS, alone significantly preserved the ventricular function of zebrafish after Dox treatment. Moreover, D006 upregulated mitochondrial biogenesis and increased mtDNA copy number after Dox treatment of H9c2 cells. D006 promoted the expression of HO-1 protein in a time-dependent manner while the HO-1 inhibitor, Znpp, reversed the protective effects of D006. In human breast tumor MCF-7 cells, D006 enhanced Dox-induced cytotoxicity by increasing apoptosis. In conclusion, our results indicate that a new DSS derivative exhibits promising protective effects against Dox-induced cardiotoxicity both in vivo and in vitro, an effect at least partially mediated by induction of HO-1 expression and the activation of mitochondrial biogenesis. Meanwhile, D006 also potentiated the anti-cancer effects of Dox in breast tumor cells.

Synthesis and biological evaluation of novel hydrogen sulfide releasing nicotinic acid derivatives

Twelve novel hybrids of slowly releasing hydrogen sulfide donor ADT-OH combined with nicotinic acid were synthesized. All of their structures had been confirmed by ¹H NMR, ¹³C NMR and MS spectra. The target compounds were evaluated for their neuroprotective effects on hippocampal neuron HT22 cells against glutamate-induced injury at the concentrations of 1-100μM with MTT assay, and their toxicity on HT22 cells untreated by glutamine at the concentration of 100μM. The active compound was further investigated for its effect on ischemic infarct volume by intraperitoneal injection at 3h after ischemia in mice models of permanent middle cerebral artery occlusion (pMCAO). The results showed that all the compounds significantly protected HT22 cells from glutamate-induced damage at most of the experimental concentrations, and had no or little neurotoxicity on normal HT22 cells at the high concentration. More importantly, compound A6 significantly reduced infarct volume in the pMCAO model. These results suggested that compound A6 may be promising for further evaluation for the intervention of cerebral ischemic injury.

Mitochondrial dysfunction remodels one-carbon metabolism in human cells

Mitochondrial dysfunction is associated with a spectrum of human disorders, ranging from rare, inborn errors of metabolism to common, age-associated diseases such as neurodegeneration. How these lesions give rise to diverse pathology is not well understood, partly because their proximal consequences have not been well-studied in mammalian cells. Here we provide two lines of evidence that mitochondrial respiratory chain dysfunction leads to alterations in one-carbon metabolism pathways. First, using hypothesis-generating metabolic, proteomic, and transcriptional profiling, followed by confirmatory experiments, we report that mitochondrial DNA depletion leads to an ATF4-mediated increase in serine biosynthesis and transsulfuration. Second, we show that lesioning the respiratory chain impairs mitochondrial production of formate from serine, and that in some cells, respiratory chain inhibition leads to growth defects upon serine withdrawal that are rescuable with purine or formate supplementation. Our work underscores the connection between the respiratory chain and one-carbon metabolism with implications for understanding mitochondrial pathogenesis.

DOI:http://dx.doi.org/10.7554/eLife.10575.001

Mitochondria are found within virtually all of our body’s cells and are best known as their power plants. Damaged mitochondria cause many diseases in humans – from rare, inherited metabolic disorders that cause symptoms including muscle weakness and developmental problems, to age-related diseases such as diabetes and Parkinson’s disease.

How does mitochondrial damage lead to such a variety of symptoms and conditions? To answer this question, researchers must understand how cells respond to and compensate for such damage.

To mimic mitochondrial failure, Bao et al. reduced the amount of DNA in the mitochondria of human cells and observed that this caused the cells to accumulate more of an amino acid called serine. Further investigation showed that this accumulation comes in part from cells producing more serine, and that a protein called Activating Transcription Factor 4 is responsible for increasing the expression of the genes needed to produce serine in the cells.

Bao et al. also found that damaged mitochondria are less able to consume serine to produce a compound called formate, which is a precursor for DNA building blocks. If cells cannot acquire enough extra serine to compensate for this inefficiency, they cannot produce some of the building blocks required to make DNA and other critical compounds in the cell. Supplementing the cells with formate or the DNA building blocks enabled the cells to recover, which suggests that formate supplements may help to treat some mitochondrial disorders.

At a higher level, these results suggest that the mitochondrion’s role as a major chemical factory in the cell, and not just as the power plant, may also contribute to disease when the mitochondria are broken. Further work is now needed to investigate how cells know to turn on Activating Transcription Factor 4 when their mitochondria are damaged. It also remains to be discovered whether this reduces or exacerbates the symptoms of mitochondrial disease.

DOI:http://dx.doi.org/10.7554/eLife.10575.002

Hydrogen Sulfide Attenuates Tissue Plasminogen Activator-Induced Cerebral Hemorrhage Following Experimental Stroke

Tissue plasminogen activator (tPA), the only approved drug for the treatment of ischemic stroke, increases the risk of cerebral hemorrhage. Here, we investigated whether the newly identified gaso-transmitter hydrogen sulfide (H2S), when used in combination with tPA, reduced the hemorrhagic transformation following stroke. In a mouse model of middle cerebral artery occlusion (MCAO), intravenous injection of tPA enhanced cerebral hemorrhage, which was significantly attenuated by the co-administration of two structurally unrelated H2S donors, ADT-OH and NaHS. By assessing extravasation of Evans blue into the ischemic hemisphere as well as brain edema following MCAO, we further showed that a tPA-exacerbated BBB disruption was significantly ameliorated by the co-administration of ADT-OH. In the mouse MCAO model, tPA upregulated Akt activation, vascular endothelial growth factor (VEGF) expression, and metalloproteinase 9 (MMP9) activity in the ischemic brain, which was remarkably attenuated by ADT-OH. In the in vitro glucose-oxygen deprivation (OGD) model, ADT-OH markedly attenuated tPA-enhanced Akt activation and VEGF expression in brain microvascular endothelial cells. Finally, ADT-OH improved functional outcomes in mice subjected to MCAO and tPA infusion. In conclusion, H2S donors reduced tPA-induced cerebral hemorrhage by possibly inhibiting the Akt-VEGF-MMP9 cascade. Administration of H2S donors has potential as a novel modality to improve the safety of tPA following stroke.

Hydrogen sulfide: physiological properties and therapeutic potential in ischaemia

Hydrogen sulfide (H2 S) has become a molecule of high interest in recent years, and it is now recognized as the third gasotransmitter in addition to nitric oxide and carbon monoxide. In this review, we discuss the recent literature on the physiology of endogenous and exogenous H2 S, focusing upon the protective effects of hydrogen sulfide in models of hypoxia and ischaemia.

Chemical tools for the study of hydrogen sulfide (H2S) and sulfane sulfur and their applications to biological studies

Hydrogen sulfide (H₂S) functions in many physiological processes, including relaxation of vascular smooth muscles, mediation of neurotransmission, inhibition of insulin signaling, and regulation of inflammation. On the other hand, sulfane sulfur, which is a sulfur atom with six valence electrons but no charge, has the unique ability to bind reversibly to other sulfur atoms to form hydropersulfides (R-S-SH) and polysulfides (-S-S_n-S-). H₂S and sulfane sulfur always coexist, and recent work suggests that sulfane sulfur species may be the actual signaling molecules in at least some biological phenomena. For example, one of the mechanisms of activity regulation of proteins by H₂S is the S-sulfhydration of cysteine residues (protein Cys-SSH). In this review, we summarize recent progress on chemical tools for the study of H₂S and sulfane sulfur, covering fluorescence probes utilizing various design strategies, H₂S caged compounds, inhibitors of physiological H₂S-producing enzymes (cystathionine γ-lyase, cystathionine β-synthase and 3-mercaptopyruvate sulfurtransferase), and labeling reagents. Fluorescence probes offer particular advantages as chemical tools to study physiological functions of biomolecules, including ease of use and real-time, nondestructive visualization of biological processes in live cells and tissues.

Thiosulfate Mediates Cytoprotective Effects of Hydrogen Sulfide Against Neuronal Ischemia

BACKGROUND

Hydrogen sulfide (H2S) exhibits protective effects in various disease models including cerebral ischemia-reperfusion (I/R) injury. Nonetheless, mechanisms and identity of molecules responsible for neuroprotective effects of H2S remain incompletely defined. In the current study, we observed that thiosulfate, an oxidation product of H2S, mediates protective effects of an H2S donor compound sodium sulfide (Na2S) against neuronal I/R injury.

METHODS AND RESULTS

We observed that thiosulfate in cell culture medium is not only required but also sufficient to mediate cytoprotective effects of Na2S against oxygen glucose deprivation and reoxygenation of human neuroblastoma cell line (SH-SY5Y) and murine primary cortical neurons. Systemic administration of sodium thiosulfate (STS) improved survival and neurological function of mice subjected to global cerebral I/R injury. Beneficial effects of STS, as well as Na2S, were associated with marked increase of thiosulfate, but not H2S, in plasma and brain tissues. These results suggest that thiosulfate is a circulating "carrier" molecule of beneficial effects of H2S. Protective effects of thiosulfate were associated with inhibition of caspase-3 activity by persulfidation at Cys163 in caspase-3. We discovered that an SLC13 family protein, sodium sulfate cotransporter 2 (SLC13A4, NaS-2), facilitates transport of thiosulfate, but not sulfide, across the cell membrane, regulating intracellular concentrations and thus mediating cytoprotective effects of Na2S and STS.

CONCLUSIONS

The protective effects of H2S are mediated by thiosulfate that is transported across cell membrane by NaS-2 and exerts antiapoptotic effects via persulfidation of caspase-3. Given the established safety track record, thiosulfate may be therapeutic against ischemic brain injury.

Farnesyltransferase inhibitor, tipifarnib, prevents galactosamine/lipopolysaccharide-induced acute liver failure

Acute liver failure (ALF) is a fatal syndrome associated with massive hepatocyte death. There is no cure for ALF except liver transplantation. Protein farnesylation is a lipid modification of cysteine residues that is catalyzed by farnesyltransferase (FTase) and has been proposed as an integral component of acute inflammation. Previously, we have demonstrated that FTase inhibitors improve survival in mouse models of endotoxemia and sepsis. Here we studied the effects of FTase inhibitor, tipifarnib, on galactosamine (GalN)/lipopolysaccharide (LPS)-induced ALF. The effects of tipifarnib (10 mg/kg, i.p.) were studied in GalN (400 mg/kg, i.p.)- and LPS (3 μg/kg)-challenged mice by histological and biochemical analyses. Galactosamine/LPS administration caused prominent liver injury characterized by the increased plasma alanine aminotransferase and aspartic aminotransferase levels, leading to significant mortality in mice. Tipifarnib inhibited GalN/LPS-induced caspase 3 activation, inflammatory cytokine production, and c-Jun N-terminal kinase phosphorylation in the liver. On the other hand, tipifarnib upregulated antiapoptotic protein, Bcl-xL, in the liver after GalN/LPS challenge. Tipifarnib also protected primary hepatocytes from GalN/tumor necrosis factor α-induced cell death by inhibiting caspase 3 activation and upregulating antiapoptotic proteins. Galactosamine/LPS-induced liver injury was associated with increased protein farnesylation in the liver. Tipifarnib prevented protein farnesylation in the liver and markedly attenuated liver injury and mortality in GalN/LPS-challenged mice. These results suggest that protein farnesylation is a novel potential molecular target to prevent hepatocyte death and acute inflammatory liver failure in fulminant hepatitis.

Hydrogen sulfide induces neuroprotection against experimental stroke in rats by down-regulation of AQP4 via activating PKC

Hydrogen sulfide (H2S) is now known as an important neuromodulator in the central nervous system. The aim of the current study was to investigate whether exogenous H2S gas can attenuate brain edema induced by experimental stroke and to clarify the potential mechanisms. Rats underwent 2-h middle cerebral artery occlusion (MCAO) and received 40 ppm or 80 ppm H2S inhalation for 3h at the beginning of reperfusion. The effects of H2S were investigated by evaluating neurological function, infarct size, brain edema volume, and aquaporin4 (AQP4) protein expression at 24h after reperfusion. Moreover, to explore the possible mechanisms for the neuroprotective effects of H2S, protein kinase C (PKC) activity was detected and a PKC inhibitor, Go6983, was used via intracerebral ventricular injection. Our results showed that 40 ppm or 80 ppm H2S inhalation significantly reduced neurological deficits, infarct size, and brain edema after MCAO. The expression of AQP4 in the peri-infarct area of brain was also inhibited after inhalation of H2S. PKC was activated by H2S treatment and the PKC inhibitor attenuated the neuroprotection of H2S with an increased AQP4 expression at the same time. In conclusion, H2S inhalation attenuates brain edema, reduces infarct volume, and improves neurologic function in a rat experimental stroke model. The therapeutic benefits of H2S inhalation are associated with down-regulation of AQP4 expression via activating PKC.