Xiao-Qing Tang

Hydrogen sulfide inhibits MPP+-induced apoptosis in PC12 cells

AIMS Hydrogen sulfide (H2S) is a well-known cytotoxic gas. Recently it has been shown to protect neurons against oxidative stress caused by glutamate, hypochlorous acid (HOCl), and beta-amyloid. The aim of the present study is to explore the cytoprotection of H2S against 1-methyl-4-phenylpyridinium ion (MPP(+))-induced apoptosis and the molecular mechanisms underlying in PC12 cells, a rat cell line derived from pheochromocytoma cells. MAIN METHODS Cell viability was determined by the conventional 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay. Apoptosis was assessed by Hoechst 33258 nuclear staining and flow cytometric (FCM) analysis after propidium iodide staining. The mitochondrial membrane potential (MMP) was measured by rhodamine 123 (Rh123) probe and reactive oxygen species (ROS) were measured by dihydrorhodamine probe using FCM analysis. KEY FINDINGS MPP(+) reduced the cell viability and induced apoptosis of PC12 cells along with dissipation of MMP as well as overproduction of ROS. Sodium hydrosulfide (NaHS), a H2S donor, protected PC12 cells against MPP(+)-induced cytotoxicity and apoptosis not only by reducing the loss of MMP, but also by attenuating an increase in intracellular ROS. SIGNIFICANCE H2S significantly protected PC12 cells against cytotoxicity and apoptosis induced by MPP(+), which was associated with the inhibition by H(2)S of MPP(+)-induced dissipation of MMP and overproduction of ROS. These findings can significantly advance therapeutic approaches to the neurodegenerative diseases which are associated with oxidative stress, such as Parkinsons disease.

Hydrogen sulfide antagonizes homocysteine-induced neurotoxicity in PC12 cells.

Hydrogen sulfide (H₂S) has been shown to protect neurons against oxidative stress. Lower levels of H(2)S as well as accumulation of homocysteine (Hcy), a strong risk of Alzheimers disease (AD), are reported in the brains of AD patients. The aim of present study is to explore the protection of H₂S against Hcy-induced cytotoxicity and apoptosis and the molecular mechanisms underlying in PC12 cells. We show that sodium hydrosulfide (NaHS), a H₂S donor, protects PC12 cells against Hcy-mediated cytotoxicity and apoptosis by preventing both the loss of mitochondrial membrane potential (MMP) and the increase in intracellular reactive oxygen species (ROS) induced by Hcy. NaHS not only promotes the expression of bcl-2, but also blocks the down-regulation of bcl-2 by Hcy. These results indicate that H₂S protects neuronal cells against neurotoxicity of Hcy by preserving MMP and attenuating ROS accumulation through up-regulation of bcl-2 level. Our study suggests a promising future of H₂S-based therapies for neurodegenerative diseases such as AD.

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

Aim:Homocysteine (Hcy) can elicit neuronal cell death, and hyperhomocysteinemia is a strong independent risk factor for Alzheimers disease. The aim of this study was to examine the effects of hydrogen sulfide (H2S) on Hcy-induced endoplasmic reticulum (ER) stress and neuronal apoptosis in rat hippocampus.Methods:Adult male SD rats were intracerebroventricularly (icv) injected with Hcy (0.6 μmol/d) for 7 d. Before Hcy injection, the rats were treated with NaHS (30 or 100 μmol·kg−1·d−1, ip) and/or k252a (1 μg/d, icv) for 2 d. The apoptotic neurons were detected in hippocampal coronal slices with TUNEL staining. The expression of glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), cleaved caspase-12, and BDNF in the hippocampus were examined using Western blotting assays. The generation of H2S in the hippocampus was measured with the NNDPD method.Results:Hcy markedly inhibited the production of endogenous H2S and increased apoptotic neurons in the hippocampus. Furthermore, Hcy induced ER stress responses in the hippocampus, as indicated by the upregulation of GRP78, CHOP, and cleaved caspase-12. Treatment with the H2S donor NaHS increased the endogenous H2S production and BDNF expression in a dose-dependent manner, and significantly reduced Hcy-induced neuronal apoptosis and ER stress responses in the hippocampus. Treatment with k252a, a specific inhibitor of TrkB (the receptor of BDNF), abolished the protective effects of NaHS against Hcy-induced ER stress in the hippocampus.Conclusion:H2S attenuates ER stress and neuronal apoptosis in the hippocampus of Hcy-treated rats via upregulating the BDNF-TrkB pathway.

Hydrogen sulfide inhibits formaldehyde-induced endoplasmic reticulum stress in PC12 cells by upregulation of SIRT-1.

Background Formaldehyde (FA), a well-known environmental pollutant, has been classified as a neurotoxic molecule. Our recent data demonstrate that hydrogen sulfide (H2S), the third gaseous transmitter, has a protective effect on the neurotoxicity of FA. However, the exact mechanisms underlying this protection remain largely unknown. Endoplasmic reticulum (ER) stress has been implicated in the neurotoxicity of FA. Silent mating type information regulator 2 homolog 1 (SIRT-1), a histone deacetylases, has various biological activities, including the extension of lifespan, the modulation of ER stress, and the neuroprotective action. Objective We hypothesize that the protection of H2S against FA-induced neurotoxicity involves in inhibiting ER stress by upregulation of SIRT-1. The present study attempted to investigate the protective effect of H2S on FA-induced ER stress in PC12 cells and the contribution of SIRT-1 to the protection of H2S against FA-induced injuries, including ER stress, cytotoxicity and apoptosis. Principal Findings We found that exogenous application of sodium hydrosulfide (NaHS; an H2S donor) significantly attenuated FA-induced ER stress responses, including the upregulated levels of glucose-regulated protein 78, C/EBP homologous protein, and cleaved caspase-12 expression. We showed that NaHS upregulates the expression of SIRT-1 in PC12 cells. Moreover, the protective effects of H2S on FA-elicited ER stress, cytotoxicity and apoptosis were reversed by Sirtinol, a specific inhibitor of SIRT-1. Conclusion/Significance These data indicate that H2S exerts its protection against the neurotoxicity of FA through overcoming ER stress via upregulation of SIRT-1. Our findings provide novel insights into the protective mechanisms of H2S against FA-induced neurotoxicity.

Hydrogen sulfide prevents formaldehyde-induced neurotoxicity to PC12 cells by attenuation of mitochondrial dysfunction and pro-apoptotic potential

Hydrogen sulfide (H(2)S) has been shown to act as a neuroprotectant and antioxidant. Numerous studies have demonstrated that exposure to formaldehyde (FA) causes neuronal damage and that oxidative stress is one of the most critical effects of FA exposure. Accumulation of FA is involved in the pathogenesis of Alzheimers disease (AD). The aim of present study is to explore the inhibitory effects of H(2)S on FA-induced cytotoxicity and apoptosis and the molecular mechanisms underlying in PC12 cells. We show that sodium hydrosulfide (NaHS), a H(2)S donor, protects PC12 cells against FA-mediated cytotoxicity and apoptosis and that NaHS preserves the function of mitochondria by preventing FA-induced loss of mitochondrial membrane potential and release of cytochrome c in PC12 cells. Furthermore, NaHS blocks FA-exerted accumulation of intracellular reactive oxygen species (ROS), down-regulation of Bcl-2 expression, and up-regulation of Bax expression. These results indicate that H(2)S protects neuronal cells against neurotoxicity of FA by preserving mitochondrial function through attenuation of ROS accumulation, up-regulation of Bcl-2 level, and down-regulation of Bax expression. Our study suggests a promising future of H(2)S-based preventions and therapies for neuronal damage after FA exposure.

A Novel Mechanism of Formaldehyde Neurotoxicity: Inhibition of Hydrogen Sulfide Generation by Promoting Overproduction of Nitric Oxide

Background Formaldehyde (FA) induces neurotoxicity by overproduction of intracellular reactive oxygen species (ROS). Increasing studies have shown that hydrogen sulfide (H2S), an endogenous gastransmitter, protects nerve cells against oxidative stress by its antioxidant effect. It has been shown that overproduction of nitric oxide (NO) inhibits the activity of cystathionine-beta-synthase (CBS), the predominant H2S-generating enzyme in the central nervous system. Objective We hypothesize that FA-caused neurotoxicity involves the deficiency of this endogenous protective antioxidant gas, which results from excessive generation of NO. The aim of this study is to evaluate whether FA disturbs H2S synthesis in PC12 cells, and whether this disturbance is associated with overproduction of NO. Principal Findings We showed that exposure of PC12 cells to FA causes reduction of viability, inhibition of CBS expression, decrease of endogenous H2S production, and NO production. CBS silencing deteriorates FA-induced decreases in endogenous H2S generation, neurotoxicity, and intracellular ROS accumulation in PC12 cells; while ADMA, a specific inhibitor of NOS significantly attenuates FA-induced decreases in endogenous H2S generation, neurotoxicity, and intracellular ROS accumulation in PC12 cells. Conclusion/Significance Our data indicate that FA induces neurotoxicity by inhibiting the generation of H2S through excess of NO and suggest that strategies to manipulate endogenous H2S could open a suitable novel therapeutic avenue for FA-induced neurotoxicity.

Formaldehyde Impairs Learning and Memory Involving the Disturbance of Hydrogen Sulfide Generation in the Hippocampus of Rats

Formaldehyde (FA), a well-known indoor and outdoor pollutant, has been implicated as the responsible agent in the development of neurocognitive disorders. Hydrogen sulfide (H2S), the third gasotransimitter, is an endogenous neuromodulator, which facilitates the induction of hippocampal long-term potentiation, involving the functions of learning and memory. In the present study, we analyzed the effects of intracerebroventricular injection of FA on the formation of learning and memory and the generation of endogenous H2S in the hippocampus of rats. We found that the intracerebroventricular injection of FA in rats impairs the function of learning and memory in the Morris water maze and novel object recognition test and increases the formation of apoptosis and lipid peroxidation in the hippocampus. We also showed that FA exposure inhibits the expression of cystathionine β-synthase, the major enzyme responsible for endogenous H2S generation in hippocampus and decreases the production of endogenous H2S in hippocampus in rats. These results suggested that FA-disturbed generation of endogenous H2S in hippocampus leads to the oxidative stress-mediated neuron damage, ultimately impairing the function of learning and memory. Our findings imply that the disturbance of endogenous H2S generation in hippocampus is a potential contributing mechanism underling FA-caused learning and memory impairment.

Inhibition of Endogenous Hydrogen Sulfide Generation is Associated with Homocysteine-Induced Neurotoxicity: Role of ERK1/2 Activation

Both elevated homocysteine and decreased hydrogen sulfide (H2S) are observed in the brains of Alzheimer’s disease (AD) patients. Reactive oxygen species (ROS) overproduction contributes to the neurotoxicity of homocysteine; however, H2S is an endogenous antioxidant gas. Therefore, the aim of this study was to investigate whether the imbalance of proportion to this endogenous protective antioxidant gas is involved in homocysteine-caused neurotoxicity. We show that homocysteine inhibits the generation of endogenous H2S and the expression and activity of cystathionine-β-synthetase (CBS), the main enzyme responsible for the generation of H2S in PC12 cells. S-Adenosylmethionine, an activator of CBS, not only prevents homocysteine-induced inhibition of endogenous H2S production but also attenuates homocysteine-triggered cytotoxicity and accumulation of ROS. We find that activation of ERK1/2 occurs in homocysteine-treated PC12 cells and blockade of ERK1/2 with U0126 abolished the homocysteine-induced cytotoxicity and inhibitory effect on endogenous H2S generation. These results indicate that homocysteine neurotoxicity involves reduction of H2S production, which is caused by inhibition of CBS and mediated by activation of ERK1/2. Our study suggests a promising future of H2S-based therapies for neurodegenerative diseases such as AD.

BDNF-TrkB pathway mediates neuroprotection of hydrogen sulfide against formaldehyde-induced toxicity to PC12 cells.

Formaldehyde (FA) is a common environmental contaminant that has toxic effects on the central nervous system (CNS). Our previous data demonstrated that hydrogen sulfide (H2S), the third endogenous gaseous mediator, has protective effects against FA-induced neurotoxicity. As is known to all, Brain-derived neurotropic factor (BDNF), a member of the neurotrophin gene family, mediates its neuroprotective properties via various intracellular signaling pathways triggered by activating the tyrosine kinase receptor B (TrkB). Intriguingly, our previous data have illustrated the upregulatory role of H2S on BDNF protein expression in the hippocampus of rats. Therefore, in this study, we hypothesized that H2S provides neuroprotection against FA toxicity by regulating BDNF-TrkB pathway. In the present study, we found that NaHS, a donor of H2S, upregulated the level of BDNF protein in PC12 cells, and significantly rescued FA-induced downregulation of BDNF levels. Furthermore, we found that pretreatment of PC12 cells with K252a, an inhibitor of the BDNF receptor TrkB, markedly reversed the inhibition of NaHS on FA-induced cytotoxicity and ablated the protective effects of NaHS on FA-induced oxidative stress, including the accumulation of intracellular reactive oxygen species (ROS), 4-hydroxy-2-trans-nonenal (4-HNE), and malondialdehyde (MDA). We also showed that K252a abolished the inhibition of NaHS on FA-induced apoptosis, as well as the activation of caspase-3 in PC12 cells. In addition, K252a reversed the protection of H2S against FA-induced downregulation of Bcl-2 protein expression and upregulation of Bax protein expression in PC12 cells. These data indicate that the BDNF-TrkB pathway mediates the neuroprotection of H2S against FA-induced cytotoxicity, oxidative stress and apoptosis in PC12 cells. These findings provide a novel mechanism underlying the protection of H2S against FA-induced neurotoxicity.

Antidepressant-like and anxiolytic-like effects of hydrogen sulfide in streptozotocin-induced diabetic rats through inhibition of hippocampal oxidative stress.

Depression is highly prevalent in individuals with diabetes, and depressive symptoms are less responsive to current antidepressant therapies. Oxidative stress plays a major role both in the pathogenesis of diabetes and in major depression and anxiety disorders. Hydrogen sulfide (H2S), the third gaseous mediator, is a novel signaling molecule in the brain that has both antioxidative activity and antidepressant-like and anxiolytic-like effects. We hypothesized that H2S could produce antidepressant-like and anxiolytic-like effects in diabetic patients through its antioxidative effect. To test this hypothesis, we generated streptozotocin (STZ)-induced diabetic rats. We found that H2S alleviated depressive-like behaviors of STZ-induced diabetic rats in the forced swimming and tail suspension tests and reduced their anxiety-like behaviors in the elevated plus maze test. We also found that H2S significantly reduced levels of malondialdehyde and 4-hydroxynonenal and elevated levels of superoxide dismutase and reduced glutathione in the hippocampus of STZ-induced diabetic rats. The results provide evidence for antidepressant-like and anxiolytic-like effects of H2S in STZ-induced diabetic rats and suggest that the therapeutic effects may result from inhibition of hippocampal oxidative stress. These findings suggest that elevating H2S signaling is a potential target for treatment of depressive and anxiety disorders related to diabetes.