Hydrogen Sulfide Attenuates Neuroinflammation by Inhibiting the NLRP3/Caspase-1/GSDMD Pathway in Retina or Brain Neuron following Rat Ischemia/Reperfusion.

Gasdermin D-executing pyroptosis mediated by NLRP3 inflammasomes has been recognized as a key pathogenesis during stroke. Hydrogen sulfide (H2S) could protect CNS against ischemia/reperfusion (I/R)-induced neuroinflammation, while the underlying mechanism remains unclear. The study applied the middle cerebral artery occlusion/reperfusion (MCAO/R) model to investigate how the brain and the retinal injuries were alleviated in sodium hydrogen sulfide (NaHS)-treated rats. The rats were assigned to four groups and received an intraperitoneal injection of 50 µmol/kg NaHS or NaCl 15 min after surgery. Neurological deficits were evaluated using the modified neurologic severity score. The quantification of pro-inflammatory cytokines, NLRP3, caspase-1, and GSDMD were determined by ELISA and Western blot. Cortical and retinal neurodegeneration and cell pyroptosis were determined by histopathologic examination. Results showed that NaHS rescued post-stroke neurological deficits and infarct progression, improved retina injury, and attenuated neuroinflammation in the brain cortexes and the retinae. NaHS administration inhibits inflammation by blocking the NLRP3/caspase-1/GSDMD pathway and further suppressing neuronal pyroptosis. This is supported by the fact that it reversed the high-level of NLRP3, caspase-1, and GSDMD following I/R. Our findings suggest that compounds with the ability to donate H2S could constitute a novel therapeutic strategy for ischemic stroke.

Role of paraoxonase-1 in the protection of hydrogen sulfide-donating sildenafil (ACS6) against homocysteine-induced neurotoxicity.

ACS6, a novel hydrogen sulfide (H2S)-releasing sildenafil, has been demonstrated to inhibit superoxide formation through donating H2S. We have previously found that ACS6 antagonizes homocysteine-induced apoptosis and cytotoxicity. The aim of the present study is to explore the molecular mechanisms underlying ACS6-exerted protective action against the neurotoxicity of homocysteine. In the present work, we used PC12 cells to explore whether paraoxonase-1 (PON-1) is implicated in ACS6-induced neuroprotection against homocysteine neurotoxicity. We show that ACS6 treatment results in prevention of homocysteine-caused neurotoxicity and overproduction of reactive oxygen species (ROS). Homocysteine downregulates the expression and activity of PON-1; however, this effect is significantly blocked by co-treatment with ACS6. The specific inhibitor of PON-1 2-hydroxyquinoline reverses the inhibitory effect of ACS6 on homocysteine-induced neurotoxicity and intracellular ROS accumulation. These results indicate that ACS6 protects PC12 cells against homocysteine-induced neurotoxicity by upregulating PON-1 and suggest a promising role of PON-1 as a novel therapeutic strategy for homocysteine-induced toxicity.

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 Alzheimer's 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.

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

BACKGROUND: The hydrogen sulfide-releasing sildenafil, ACS6, has been demonstrated to inhibit superoxide formation through donating hydrogen sulfide (H2S). We have found that H2S antagonizes homocysteine-induced oxidative stress and neurotoxicity. The aim of the present study is to explore the protection of ACS6 against homocysteine-triggered cytotoxicity and apoptosis and the molecular mechanisms underlying in PC12 cells. METHODS: Cell viability was determined by Cell Counting Kit-8 assay. Cell apoptosis was observed using the chromatin dye Hoechst 33258 and analyzed by Flow Cytometry after propidium iodide staining. Mitochondrial membrane potential was monitored using the fluorescent dye Rh123. Intracellular reactive oxygen species were determined by oxidative conversion of cell permeable 2',7'-dichlorfluorescein-diacetate to fluorescent 2',7'-dichlorfluorescein. The expression of cleaved caspase-3 and bcl-2 and the accumulation of cytosolic cytochrome c were analyzed by Western blot. RESULTS: We show that ACS6 protects PC12 cells against cytotoxicity and apoptosis induced by homocysteine and blocks homocysteine-triggered cytochrome c release and caspase-3 activation. ACS6 treatment results in not only prevention of homocysteine-caused mitochondrial membrane potential (Δψ) loss and reactive oxygen species (ROS) overproduction but also reversal of Bcl-2 down-expression. CONCLUSIONS: These results indicate that ACS6 protects PC12 cells against homocysteine-induced cytotoxicity and apoptosis by preservation of mitochondrial function though inhibiting both loss of Δψ and accumulation of ROS as well as modulating the expression of Bcl-2. Our study provides evidence both for a neuroprotective effect of ACS6 and for further evaluation of ACS6 as novel neuroprotectants for Alzheimer's disease associated with homocysteine.

Endogenous hydrogen sulfide is involved in asymmetric dimethylarginine-induced protection against neurotoxicity of 1-methyl-4-phenyl-pyridinium ion.

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, is profoundly protective against 1-methy-4-phenylpyridinium ion (MPP+)-induced neurotoxicity. Reactive oxygen species (ROS) overproduction contributes to the neurotoxicity of MPP+; while hydrogen sulfide (H2S) is a pivotal endogenous antioxidant. This study is to assess the potential role of endogenous H2S in the neuroprotection of ADMA against MPP+-induced toxicity in PC12 cells. We showed that ADMA prevented MPP+-induced inhibition of endogenous H2S generation through inhibiting the down-regulation of cystathionine-ß-synthetase (CBS, the major enzyme responsible for endogenous H2S generation in PC12 cells) expression and activity elicited by MPP+. ADMA obviously attenuated MPP+-triggered accumulation of intracellular ROS, dissipation of mitochondrial membrane potential (MMP), release of cytochrome c (Cyt-c), and downregulation of Bcl-2 protein expression in PC12 cells. Inhibition of CBS activity by amino-oxyacetate and CBS silencing with a short hairpin RNA vector targeting rat CBS gene reversed the protective action of ADMA against MPP+-caused cytotoxicity, ROS overproduction, and MMP loss in PC12 cells. These results indicate that the protection of ADMA against MPP+-mediated neurotoxicity involves the melioration of MPP+-induced inhibition of endogenous H2S generation. Our findings suggest that modulation of H2S production provide new therapeutic targets for the treatment of neurodegenerative disease, such as Parkinson's disease.

Formaldehyde induces neurotoxicity to PC12 cells involving inhibition of paraoxonase-1 expression and activity.

1. Formaldehyde (FA) has been found to cause toxicity to neurons. However, its neurotoxic mechanisms have not yet been clarified. Increasing evidence has shown that oxidative damage is one of the most critical effects of formaldehyde exposure. Paraoxonase-1 (PON-1) is a pivotal endogenous anti-oxidant. Thus, we hypothesized that FA-mediated downregulation of PON1 is associated with its neurotoxicity. 2. In the present work, we used PC12 cells to study the neurotoxicity of FA and explore whether PON-1 is implicated in FA-induced neurotoxicity. 3. We found that FA has potent cytotoxic and apoptotic effects on PC12 cells. FA induces an accumulation of intracellular reactive oxygen species along with downregulation of Bcl-2 expression, as well as increased cytochrome c release. FA significantly suppressed the expression and activity of PON-1 in PC12 cells. Furthermore, H(2)S, an endogenous anti-oxidant gas, antagonizes FA-induced cytotoxicity as well as 2-hydroxyquinoline, a specific inhibitor of PON-1, which also induces cytotoxicity to PC12 cells. 4. The results of the present study provide, for the first time, evidence that the inhibitory effect on PON-1 expression and activity is involved in the neurotoxicity of FA, and suggest a promising role of PON-1 as a novel therapeutic strategy for FA-mediated toxicity.

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

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

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 Alzheimer's 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.