Gastrodin protects against glutamate-induced ferroptosis in HT-22 cells through Nrf2/HO-1 signaling pathway

Gastrodin (GAS) is a component of Gastrodia elata Blume, with strong antioxidant activity in neurodegenerative diseases. Ferroptosis is similar to glutamate-induced cell death. This study was designed to explore the protective effects of GAS against glutamate-induced neurotoxicity in mice hippocampal neurons (HT-22) cells. HT-22 cells were cultured with glutamate in the presence or absence of GAS (1, 5, 25 μM). Results showed that GAS inhibited glutamate-induced ferroptosis via Nrf2/HO-1 signaling pathway. Pretreatment of HT-22 cells with GAS significantly decreased glutamate-induced cell death and release of LDH. Ferrostatin-1, liproxstatin-1, and DFO treatments canceled these effect. GAS decreased glutamate-treatment ROS production in HT-22 cells. The concentration of iron ion was analyzed using ICP-MS. Metal analysis showed that GAS pretreatment normalized iron ion concentration in HT-22 cells. We found that GAS increased the nuclear translocation of Nrf2, up-regulated the downstream HO-1 protein expression in HT-22 cells following treatment with glutamate. Nrf2 knockdown greatly decreased glutamate-induced ferroptosis through HO-1. In conclusion, these results show that GAS protects HT-22 cells from the ferroptosis induced by glutamate through a new mechanism of Nrf2/HO-1 signaling pathway.     

Effects of Resveratrol and trans-3,5,4’-Trimethoxystilbene on Glutamate-Induced Cytotoxicity,Heme Oxygenase-1, and Sirtuin 1 in HT22 Neuronal Cells

Resveratrol (trans-3,5,4’-trihydroxystilbene) has received considerable attention recently for the potential neuroprotective effects in neurodegenerative disorders where heme oxygenase-1 (HO-1) and sirtuin 1 (SIRT1) represent promising therapeutic targets. Resveratrol has been known to increase HO-1 expression and SIRT1 activity. In this study, the effects of resveratrol and trans-3,5,4’-trimethoxystilbene (TMS), a resveratrol derivative, on cytotoxicity caused by glutamate-induced oxidative stress, HO-1 expression, and SIRT1 activation have been investigated by using murine hippocampal HT22 cells, which have been widely used as an in vitro model for investigating glutamate-induced neurotoxicity. Resveratrol protected HT22 neuronal cells from glutamateinduced cytotoxicity and increased HO-1 expression as well as SIRT1 activity in a concentration-dependent manner. Cytoprotec-tion afforded by resveratrol was partially reversed by the specific inhibition of HO-1 expression by HO-1 small interfering RNA and the nonspecific blockage of HO-1 activity by tin protoporphyrin IX, but not by SIRT1 inhibitors. Surprisingly, TMS, a resveratrol derivative with methoxyl groups in lieu of the hydroxyl groups, and trans-stilbene, a non-hydroxylated analog, failed to protect HT22 cells from glutamate-induced cytotoxicity and to increase HO-1 expression and SIRT1 activity. Taken together, our findings suggest that the cytoprotective effect of resveratrol was at least in part associated with HO-1 expression but not with SIRT1 activation and, importantly, that the presence of hydroxyl groups on the benzene rings of resveratrol appears to be necessary for cytoprotection against glutamate-induced oxidative stress, HO-1 expression, and SIRT1 activation in HT22 neuronal cells.     

Acanthopanax senticosus exerts neuroprotective effects through HO-1 signaling in hippocampal and microglial cells

Extracts of Acanthopanax senticosus, a traditional herb commonly found in Northeastern Asia, are used for treating neurodegenerative disorders such as ischemia and depression. However, the mechanisms of its neuroinflammatory and cytoprotective effects have not been investigated. We examined the mechanism of A. senticosus activity in anti-neuroinflammatory and neuroprotective processes. HO-1 is an inducible enzyme present in most cell lines. ASE increased HO-1 expression, which reduced LPS-induced nitric oxide/ROS production in BV2 cells. Moreover, the induction of HO-1 expression protected cells against glutamate-induced neuronal cell death. Activation of the p38-CREB pathway and translocation of Nrf2 are strongly involved in ASE-induced HO-1 expression. Our results showed that ASE-induced HO-1 expression through the p38-CREB pathway plays an important role in the generation of anti-neuroinflammatory and neuroprotective responses. ASE also increases the translocation of Nrf2 to regulate HO-1 expression. Furthermore, our results indicate that ASE serves as a potential therapeutic agent for neuronal disorders.     

Neuroprotective effects of constituents of the root bark of <Emphasis Type="Italic">Dictamnus dasycarpus</Emphasis> in mouse hippocampal cells

Glutamate-induced oxidative injury causes neuronal degeneration related to many central nervous system diseases, such as Parkinson’s disease, Alzheimer’s disease, epilepsy and ischemia. The bioassay-guided fractionation of the EtOH extract of the root bark of Dictamnus dasycarpus Trucz. provided one neuroprotective limonoid, obacunone, together with a degraded limonoid, fraxinellone and two alkaloids, dictamine and haplopine. At concentrations of 100–150 μM, obacunone showed the potent neuroprotective effects on glutamateinduced neurotoxicity and induced the expression of heme oxygenase (HO)-1 in the mouse hippocampal HT22 cells. In addition, we found that obacunone increased p38 MAPK phosphorylation and induced HO-1 expression via p38 MAPK pathway. These results suggest that obacunone isolated from the root bark of D. dasycarpus increases cellular resistance to glutamate-induced oxidative injury in mouse hippocampal HT22 cells, presumably through the p38 MAPK pathway-dependent HO-1 expression. These results suggest that obacunone could be the effective candidates for the treatment of ROS-related neurological diseases.     

Neuroprotective and anti-inflammatory effects of mollugin via up-regulation of heme oxygenase-1 in mouse hippocampal and microglial cells

Mollugin, a bioactive phytochemical isolated from Rubia cordifolia L. (Rubiaceae), exhibits antimutagenic activity, antitumor activity, antiviral activity, and inhibitory activity in arachidonic acid- and collagen-induced platelet aggregation. In this study, we investigated the effects of mollugin as a neuroprotective agent in glutamate-induced neurotoxicity in the mouse hippocampal HT22 cell line and as an anti-inflammatory agent in lipopolysaccharide-induced microglial activation in BV2 cells. Mollugin showed potent neuroprotective effects against glutamate-induced neurotoxicity and reactive oxygen species generation in mouse hippocampal HT22 cells. In addition, the anti-inflammatory effects of mollugin were demonstrated by the suppression of pro-inflammatory mediators, including pro-inflammatory enzymes (inducible nitric oxide synthase and cyclooxygenase-2) and cytokines (tumor necrosis factor-α and interleukin-6). Furthermore, we found that the neuroprotective and anti-inflammatory effects of mollugin were linked to the up-regulation of the expression of heme oxygenase (HO)-1 and the activity of HO in HT22 and BV2 cells. In addition, the effects of mollugin resulted in the nuclear accumulation of nuclear factor-E2-related factor 2 (Nrf2) in HT22 and BV2 cells. Furthermore, mollugin also activated the p38 mitogen-activated protein kinase (MAPK) pathway both in HT22 and BV2 cells. These results suggest that mollugin may be a promising candidate for the treatment of neurodegenerative diseases related to neuroinflammation.     

Copper induces oxidative stress and apoptosis of hippocampal neuron via pCREB/BDNF/ and Nrf2/HO-1/NQO1 pathway

Disordered copper metabolism has been suggested to occur to several neurological conditions, including Alzheimer's disease and Parkinson's disease. However, the underlying mechanism was still unclear. This might link to copper-induced hippocampal neuronal apoptosis and decrease in neurons viability. Our vitro experiment showed copper exposure induced oxidative stress and promoted apoptosis of HT22 murine hippocampal neuronal cell. Mechanistically, we found copper, on the one hand, prevented phosphorylation of cAMP response element binding protein (CREB) to decrease expression its downstream target protein Brain-derived neurotrophic factor (BDNF), and to decrease mitochondrial membrane potential and Bcl-2/Bax ratio; on the other hand, copper-induced reactive oxygen species (ROS), promoted lipid peroxidation, reduced antioxidant enzyme activity of GSH-Px. Copper-induced oxidative damage further decreased the phosphorylation of CREB, decreased expression of Bcl-2, enhanced expression of Bax, and accelerated the dissociation of keap1-Nrf2 complex, promoted the nuclear translocation of Nrf2, stimulate the expression of antioxidant molecules HO-1 and NQO1. In conclusion, we found copper inhibited pCREB/BDNF signaling pathway by prevent CREB from phosphorylation, further found that oxidative damage not only inhibited neuroprotective signaling pathways and induced apoptosis, but activated antioxidant protection signals Nrf2/HO-1/NQO1 signaling pathway.     

Neuroprotective Effect of Steamed and Fermented Codonopsis lanceolata

Codonopsis lanceolata has been used as an herbal medicine for several lung inflammatory diseases, such as asthma, tonsillitis, and pharyngitis. Previously, we showed the neuroprotective effect of steamed and fermented C. lanceolata (SFC) in vitro and in vivo. In the current study, the treatment of HT22 cells with SFC decreased glutamate-induced cell death, suggesting that SFC protected HT22 cells from glutamate-induced cytotoxicity. Based on these, we sought to elucidate the mechanisms of the neuro-protective effect of SFC by measuring the oxidative stress parameters and the expression of Bax and caspase-3 in HT22 cells. SFC reduced contents of ROS, Ca²⁺ and NO. Moreover, SFC restored contents of glutathione and glutathione reductase as well as inhibited Bax and caspase-3 activity in HT22 cells. These results indicate that steamed and fermented C. lanceolata (SFC) extract protected HT22 cells by anti-oxidative effect and inhibition of the expression of Bax and caspase-3.     

Attenuation of Aβ25–35-induced parallel autophagic and apoptotic cell death by gypenoside XVII through the estrogen receptor-dependent activation of Nrf2/ARE pathways

Amyloid-beta (Aβ) has a pivotal function in the pathogenesis of Alzheimer's disease. To investigate Aβ neurotoxicity, we used an in vitro model that involves Aβ_25–35-induced cell death in the nerve growth factor-induced differentiation of PC12 cells. Aβ_25–35 (20 μM) treatment for 24 h caused apoptotic cell death, as evidenced by significant cell viability reduction, LDH release, phosphatidylserine externalization, mitochondrial membrane potential disruption, cytochrome c release, caspase-3 activation, PARP cleavage, and DNA fragmentation in PC12 cells. Aβ_25–35 treatment led to autophagic cell death, as evidenced by augmented GFP-LC3 puncta, conversion of LC3-I to LC3-II, and increased LC3-II/LC3-I ratio. Aβ_25–35 treatment induced oxidative stress, as evidenced by intracellular ROS accumulation and increased production of mitochondrial superoxide, malondialdehyde, protein carbonyl, and 8-OHdG. Phytoestrogens have been proved to be protective against Aβ-induced neurotoxicity and regarded as relatively safe targets for AD drug development. Gypenoside XVII (GP-17) is a novel phytoestrogen isolated from Gynostemma pentaphyllum or Panax notoginseng. Pretreatment with GP-17 (10 μM) for 12 h increased estrogen response element reporter activity, activated PI3K/Akt pathways, inhibited GSK-3β, induced Nrf2 nuclear translocation, augmented antioxidant responsive element enhancer activity, upregulated heme oxygenase 1 (HO-1) expression and activity, and provided protective effects against Aβ_25–35-induced neurotoxicity, including oxidative stress, apoptosis, and autophagic cell death. In conclusion, GP-17 conferred protection against Aβ_25–35-induced neurotoxicity through estrogen receptor-dependent activation of PI3K/Akt pathways, inactivation of GSK-3β and activation of Nrf2/ARE/HO-1 pathways. This finding might provide novel insights into understanding the mechanism for neuroprotective effects of phytoestrogens or gypenosides.     

Sanguinarine induces apoptosis in human colorectal cancer HCT-116 cells through ROS-mediated Egr-1 activation and mitochondrial dysfunction

We examined the effects of sanguinarine, a benzophenanthridine alkaloid, on reactive oxygen species (ROS) production and the association of these effects with apoptotic cell death in a human colorectal cancer HCT-116 cell line. Sanguinarine generated ROS, which was followed by a decrease in the mitochondrial membrane potential (MMP), the activation of caspase-9 and -3, and the down-regulation of anti-apoptotic proteins, such as Bcl2, XIAP and cIAP-1. Sanguinarine also promoted the activation of caspase-8 and truncation of Bid (tBid). However, the quenching of ROS generation by N-acetyl-l-cysteine, a scavenger of ROS, reversed the sanguinarine-induced apoptosis effects via inhibition of the MMP collapse, tBid expression, and activation of caspases. Sanguinarine also markedly induced the expression of the early growth response gene-1 (Egr-1) during the early period, after which expression level was decreased. In addition, HCT-116 cells transfected with Egr-1 siRNA displayed significant blockage of sanguinarine-induced apoptotic activity in a ROS-dependent manner. These observations clearly indicate that ROS, which are key mediators of Egr-1 activation and MMP collapse, are involved in the early molecular events in the sanguinarine-induced apoptotic pathway acting in HCT-116 cells.     

Lavandulyl flavanones from Sophora flavescens protect mouse hippocampal cells against glutamate-induced neurotoxicity via the induction of heme oxygenase-1

Lavandulyl flavanones of Sophora flavescens roots are anti-malarial, anti-inflammatory, and cytotoxic. Here, we examined whether four lavandulyl flavanones, (2S)-2'-methoxykurarinone (1), sophoraflavanone G (2), leachianone A (3), and (-)-kurarinone (4), isolated from S. flavescens could protect HT22 immortalized hippocampal cells against glutamate-induced oxidative stress. Compounds 1 and 2 induced the expression of heme oxygenase (HO)-1 and increased HO activity dose- and time-dependently. These two compounds also suppressed glutamate-induced reactive oxygen species generation in HT22 cells, whereas compounds 3 and 4 were not protective. These two lavandulyl flavanones (compounds 1, 2) may protect against glutamate-induced neurotoxicity via HO-1 induction.     

Spermidine prevents high glucose‐induced senescence in HT‐22 cells by upregulation of CB1 receptor

Hyperglycaemia‐induced neurotoxicity involved in the pathogenesis of diabetic encephalopathy and neuronal senescence is one of the worst effects of hyperglyceamic neurotoxicity. Cannabinoid receptor type 1 (CB1) has neuroprotective function in a series of neuropathy. Spermidine (Spd) has anti‐aging function in many tissues. However, the role of Spd in hyperglyceamia‐induced neuronal senescence remains unexplored. Therefore, we used high glucose (HG)‐treated HT‐22 cell as vitro model to investigate whether Spd protects neurons against hyperglyceamia‐induced senescence and the mediatory role of CB1 receptor. The HT‐22 cells were cultured in HG condition in the presence of different dose of Spd. Then, the viability of cells was measured by Cell Counting Kit‐8 (CCK‐8) assay. The senescence of cells was detected by Senescence‐associated β‐galactosidase (SA‐β‐Gal) staining. The expressions of p16^INK4a, p21^CIP1 and CB1 receptor were measured by western blot. We found that Spd inhibited HG‐induced neurotoxicity (the loss of cell viability) and senescence (the increase of SA‐β‐Gal positive cells, the upregulation of p16^INK4a and p21^CIP1) in HT‐22 cells. Also, Spd prevented HG‐induced downregulation of CB1 receptor in HT‐22 cells. Furthermore, we demonstrated that AM251 (a specific inhibitor of the CB1 receptor) reversed the protective effects of Spd on HG‐induced neurotoxicity and senescence. These results indicated that Spd prevents HG‐induced neurotoxicity and senescence via the upregulation of CB1 receptor. Our findings provide a promising future of Spd‐based preventions and therapies for diabetic encephalopathy.     

Thymoquinone induces heme oxygenase-1 expression in HaCaT cells via Nrf2/ARE activation: Akt and AMPKα as upstream targets

Thymoquinone (TQ), an active constituent of Nigella sativa, possesses anti-inflammatory and anticancer properties. Multiple lines of evidence suggest that the induction of heme oxygenase-1 (HO-1) suppresses inflammation and carcinogenesis. In the present study, we examined the effect of TQ on HO-1 expression in human keratinocytes (HaCaT) and elucidated its underlying molecular mechanisms. TQ induced the expression of HO-1 in HaCaT cells in a concentration- and time-dependent manner. Treatment with TQ increased the localization of nuclear factor (NF)-erythroid2-(E2)-related factor-2 (Nrf2) in the nucleus and elevated the antioxidant response element (ARE)-reporter gene activity. Knockdown of Nrf2 abrogated TQ-induced HO-1 expression and the ARE luciferase activity. TQ induced the phosphorylation of extracellular signal-regulated kinase (ERK), Akt and cyclic AMP-activated protein kinase-α (AMPKα). Pharmacological inhibition of Akt or AMPKα, but not that of ERK, abrogated TQ-induced nuclear localization of Nrf2, the ARE-luciferase activity and the expression of HO-1. TQ also generated reactive oxygen species (ROS) and pretreatment with N-acetyl cysteine (NAC) abrogated TQ-induced ROS accumulation, Akt and AMPKα activation, Nrf2 nuclear localization, the ARE-luciferase activity, and HO-1 expression in HaCaT cells. Taken together, TQ induces HO-1 expression in HaCaT cells by activating Nrf2 through ROS-mediated phosphorylation of Akt and AMPKα.     

Cudratricusxanthone A protects mouse hippocampal cells against glutamate-induced neurotoxicity via the induction of heme oxygenase-1

Cudratricusxantone A (CTXA), isolated from the roots of Cudrania tricuspidata Bureau (Moraceae), has potent hepatoprotective, antiproliferative, and monoamine oxidase inhibitory effects. In this study, we examined whether CTXA could protect HT22-immortalized hippocampal cells against glutamate-induced oxidative stress through the induction of heme oxygenase (HO)-1 expression. CTXA induced the expression of HO-1 and increased HO activity dose- and time-dependently. CTXA also suppressed glutamate-induced ROS generation in HT22 cells. Interestingly, treatment of neuronal cells with CTXA enhanced cellular resistance to glutamate oxidative stress. The protective effect of CTXA was abrogated by tin protoporphyrin IX, an HO inhibitor. In addition, treatment with the HO-1 inducer, cobalt protoporphyrin IX, and bilirubin, one of the enzymatic products of HO-1, produced comparable protection. These results demonstrate that CTXA protects neuronal cells from glutamate-induced oxidative stress via the induction of HO-1.     

Critical role of the JNK-p53-GADD45α apoptotic cascade in mediating oxidative cytotoxicity in hippocampal neurons

BACKGROUND AND PURPOSE

Glutamate-induced oxidative stress plays a critical role in the induction of neuronal cell death in a number of disease states. We sought to determine the role of the c-Jun NH₂-terminal kinase (JNK)-p53-growth arrest and DNA damage-inducible gene (GADD) 45α apoptotic cascade in mediating glutamate-induced oxidative cytotoxicity in hippocampal neuronal cells.

EXPERIMENTAL APPROACH

HT22 cells, a mouse hippocampal neuronal cell line, were treated with glutamate to induce oxidative stress in vitro. Kainic acid-induced oxidative damage to the hippocampus in rats was used as an in vivo model. The signalling molecules along the JNK-p53-GADD45α cascade were probed with various means to determine their contributions to oxidative neurotoxicity.

KEY RESULTS

Treatment of HT22 cells with glutamate increased the mRNA and protein levels of GADD45α, and these increases were suppressed by p53 knock-down. Knock-down of either p53 or GADD45α also prevented glutamate-induced cell death. Glutamate-induced p53 activation was preceded by accumulation of reactive oxygen species, and co-treatment with N-acetyl-cysteine prevented glutamate-induced p53 activation and GADD45α expression. Knock-down of MKK4 or JNK, or the presence of SP600125 (a JNK inhibitor), each inhibited glutamate-induced p53 activation and GADD45α expression. In addition, we also confirmed the involvement of GADD45α in mediating kainic acid-induced hippocampal oxidative neurotoxicity in vivo.

CONCLUSIONS AND IMPLICATIONS

Activation of the JNK-p53-GADD45α cascade played a critical role in mediating oxidative cytotoxicity in hippocampal neurons. Pharmacological inhibition of this signalling cascade may provide an effective strategy for neuroprotection.     

Involvement of heme oxygenase-1 induction in the cytoprotective and immunomodulatory activities of 6,4'-dihydroxy-7-methoxyflavanone in murine hippocampal and microglia cells

6,4'-Dihydroxy-7-methoxyflavanone (DMF), a biologically active compound, was isolated from the heartwood of Dalbergia odorifera T. Chen (Leguminosae). The present study proposed to examine the role of DMF as an anti-oxidative and anti-inflammatory heme oxygenase-1 (HO-1) inducer in mouse hippocampal HT22 cells and BV2 microglia cells. The effect of DMF on cell viability was determined by MTT assay and the effects of DMF on pro-inflammatory enzymes and cytokines were analyzed by western blot and ELISA. Parameters such as DMF induced HO-1 protein immunocontents, HO activity and mitogen-activated protein kinases (MAPK) activation were also measured. DMF increased cellular resistance to oxidative injury caused by glutamate-induced cytotoxicity in HT22 cells, via JUN N-terminal kinase (JNK) pathway dependent HO-1 expression. Furthermore, DMF suppressed the lipopolysaccharide (LPS)-induced expression of pro-inflammatory enzymes and inflammatory mediators in BV2 microglia. DMF suppressed production of nitric oxide (NO), prostaglandin E2 (PGE(2)), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), through extracellular signal-regulated kinase (ERK) pathway dependent HO-1 expression. This study indicates that DMF effectively modulates the regulation of anti-oxidative and anti-inflammatory action, via up-regulation of HO-1 in HT22 cells and BV2 microglia. These results suggest that DMF possesses therapeutic potentials against neurodegenerative diseases that are induced by oxidative stress and neuroinflammation.