Isolation and Purification of Harpagogenin as an Nrf2-ARE Activator from the Tubers of Chinese Artichoke (Stachys sieboldii).

Chinese artichoke tuber (Stachys sieboldii Miq.) is used as an herbal medicine as well as edible food. This study examined the effect of the Chinese artichoke extracts on the nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway that induces the expression of antioxidant enzymes to explore its novel characteristics. Hot water extracts exhibited relatively high ARE activity. ARE activity was observed in two fractions when the hot water extracts were separated in the presence of trifluoroacetic acid using HPLC. Conversely, the highly active fraction disappeared when the hot water extracts were separated in the absence of trifluoroacetic acid. These results indicate that acidic degradation produces active ingredients. The structural analysis of the two active fractions identified harpagide, which is an iridoid glucoside, and harpagogenin. In vitro experiments revealed that harpagide was converted into harpagogenin under acidic conditions and that harpagogenin, but not harpagide, had potent ARE activity. Therefore, this study identified harpagogenin, which is an acid hydrolysate of harpagide, as an ARE activator and suggests that Nrf2-ARE pathway activation by Chinese artichoke contributes to the antioxidative effect.

TPNA10168, an Nrf-2 activator, attenuates inflammatory responses independently of Nrf2 in microglial BV-2 cells: Involvement of the extracellular-signal-regulated kinase pathway.

Some chemical Nrf2 inducers possess antioxidant and anti-inflammatory properties. TPNA10168, which was identified from a chemical library as a potential activator of the Keap1-Nrf2-ARE pathway, exhibits a neuroprotective effect against oxidative stress-induced injury. However, it has not been investigated as an anti-inflammatory agent. Here we examined the effect of TPNA10168 on interferon-γ-induced proinflammatory gene expression in mouse microglial BV-2 cells. TPNA10168 significantly reduced the transcription of inflammatory genes, including TNF-α, IL-1ß, IL-6, and iNOS; however, the inhibition of proinflammatory cytokine gene expression was not attenuated by inhibitors of Nrf2-regulated enzymes. Furthermore, TPNA10168 showed anti-inflammatory effects, even in Nrf2-deficient cells, and inhibited interferon-γ-induced phosphorylation of extracellular-signal-regulated kinase (ERK). Studies with an ERK pathway inhibitor demonstrated a role for ERK in the transcription of inflammatory genes. These results suggest that TPNA10168 attenuates microglial proinflammatory activation independently of Nrf2, at least in part, by suppressing interferon-γ-induced ERK signaling.

Therapeutic effect of a novel curcumin derivative GT863 on a mouse model of amyotrophic lateral sclerosis.

The present study investigated the therapeutic effects of the curcumin derivative 3-[(1E)-2-(1H-indol-6-yl)ethenyl]-5-[(1E)-2-[2-methoxy-4-(2-pyridylmethoxy)phenyl]ethenyl]-1H-pyrazole (GT863) in amyotrophic lateral sclerosis (ALS). The inhibitory effect of GT863 on superoxide dismutase 1 (SOD1) aggregation was evaluated in cell-free assays. GT863 interfered with the conformational changes of the SOD1 protein and later, oligomeric aggregation. Furthermore, its antioxidant, anti-inflammatory, and neuroprotective effects were evaluated in cell-free and cultured cell assays. GT863 inhibited H2O2- and glutamate-induced cytotoxicity and activated an antioxidant responsive element pathway. Additionally, in vivo effects of GT863 in the ALS mice model were evaluated by its oral administration to H46R mutant SOD1 transgenic mice. Rotarod test showed that GT863 administration significantly slowed the progression of motor dysfunction in the mice. In addition, GT863 substantially reduced highly-aggregated SOD1, further preserving large neurons in the spinal cord of GT863-treated mice. Collectively, these results indicated that GT863 could be a viable therapeutic agent with multiple vital actions for the treatment of ALS.

Establishing a high throughput drug screening system for cerebral ischemia using zebrafish larvae.

We previously generated an ischemic stroke in a zebrafish model using N2 gas perfusion; however, this model was an unsuitable drug screening system due to low throughput. In this study, we examined a zebrafish ischemic stroke model using an oxygen absorber to assess drug effects. Hypoxic exposure more than 2 h using the oxygen absorber significantly induced cell death in the brain and damage to the neuronal cells. To confirm the utility of the ischemic model induced by the oxygen absorber, we treated zebrafish with neuroprotective agents. MK-801, an N-methyl-d-aspartate (NMDA) receptor antagonist, significantly suppressed cell death in the brain, and edaravone, a free radical scavenger, significantly reduced the number of dead cells. These results suggest that the activation of NMDA receptors and the production of reactive oxygen species induce neuronal cell damage in accordance with previous mammalian reports. We demonstrate the suitability of an ischemic stroke model in zebrafish larvae using the oxygen absorber, enabling a high throughput drug screening.

In vivo brain ischemia-reperfusion model induced by hypoxia-reoxygenation using zebrafish larvae.

Cerebral infarct is caused by cerebrovascular occlusion and results in brain damage. Although many rodent models of cerebral infarct exist, there is none based on zebrafish. In this study, we developed a novel ischemia-reperfusion model induced by hypoxic treatment using zebrafish. We first examined the changes in blood flow under hypoxic conditions. Hypoxic treatment interrupted the blood flow in 4 dpf (days post fertilization) zebrafish larvae. To quantify the trunk and cerebral blood flow, we selected the middle mesencephalic central artery (MMCtA) as a cerebral blood vessel and the dorsal aorta (DA) as a blood vessel of the trunk. Interestingly, the interruption of blood flow in MMCtA preceded that in DA. Considering these results, we hypothesized that reoxygenation immediately after hypoxia-induced cerebral ischemia leads to reperfusion. As a result, hypoxia-reoxygenation (H/R) treatment induced ischemia-reperfusion in cerebral vessels. Furthermore, brain cell death was increased 24 h after H/R treatment. Transgenic zebrafish (HuC:kaede), with neuronal cells expressing the kaede fluorescent protein, was used to investigate the effect of H/R on neuronal cells. The H/R treatment reduced the fluorescence intensity of kaede. Besides, glial fibrillary acidic protein immunoreactivity in H/R-treated larvae was significantly increased. In conclusion, H/R-treated zebrafish larvae may provide a novel ischemia-reperfusion model.

Protective effects of Nrf2-ARE activator on dopaminergic neuronal loss in Parkinson disease model mice: Possible involvement of heme oxygenase-1.

Parkinson disease (PD) is a neurodegenerative disorder characterized by a selective loss of dopaminergic neurons in the substantia nigra, and oxidative stress is thought to contribute to this pathogenesis. The nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway, which induces the production of antioxidant enzymes, is thereby a potential target for therapeutics to reduce neurodegeneration in PD. Previously, we identified TPNA10168 from a chemical library as an activator of the Nrf2-ARE pathway, and the present study examined the effects of TPNA10168 on an in vivo PD model. Subcutaneous administration of TPNA10168 was associated with inhibited dopaminergic neuronal loss and behavioral impairment in 6-hydroxydopamine-induced PD model mice. Heme oxygenase-1 (HO-1) is an antioxidant enzyme expressed downstream of the Nrf2-ARE signaling pathway, and we observed that HO-1 protein levels were upregulated by TPNA10168 in the mouse brain. These results suggest that TPNA10168 inhibits dopaminergic neuronal death in PD model mice, and that upregulation of HO-1 might participate in this effect.

Protective Effect of 2',3'-Dihydroxy-4',6'-dimethoxychalcone on Glutamate-Induced Neurotoxicity in Primary Cortical Cultures.

We have previously isolated 2',3'-dihydroxy-4',6'-dimethoxychalcone (DDC) from green perilla leaves as the activator of the nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway. This study aims to evaluate the effects of DDC against glutamate neurotoxicity using rat primary cortical cultures. Treatment of cultures with DDC for 24 h before glutamate exposure significantly inhibited glutamate neurotoxicity in a concentration-dependent manner. The involvement of hemeoxygenase-1 (HO-1) and reduced glutathione (GSH) in the protective effects of DDC on cortical cultures was also evaluated. While an HO-1 inhibitor did not have a significant effect on DDC-induced neuroprotection, a γ-glutamylcystein synthetase (γ-GCS) inhibitor significantly suppressed the protective effect of DDC. In an astrocyte culture, DDC induced a marked increase in the levels of intracellular reduced GSH. These results suggest that DDC mainly activates the Nrf2-ARE pathway of astrocytes, resulting in the increased extracellular release of reduced GSH, protecting neurons from glutamate neurotoxicity.

α-Synuclein oligomers mediate the aberrant form of spike-induced calcium release from IP3 receptor.

Emerging evidence implicates α-synuclein oligomers as potential culprits in the pathogenesis of Lewy body disease (LBD). Soluble oligomeric α-synuclein accumulation in cytoplasm is believed to modify neuronal activities and intraneural Ca2+ dynamics, which augment the metabolic burden in central neurons vulnerable to LBD, although this hypothesis remains to be fully tested. We evaluated how intracellular α-synuclein oligomers affect the neuronal excitabilities and Ca2+ dynamics of pyramidal neurons in neocortical slices from mice. Intracellular application of α-synuclein containing stable higher-order oligomers (αSNo) significantly reduced spike frequency during current injection, elongated the duration of spike afterhyperpolarization (AHP), and enlarged AHP current charge in comparison with that of α-synuclein without higher-order oligomers. This αSNo-mediated alteration was triggered by spike-induced Ca2+ release from inositol trisphosphate receptors (IP3R) functionally coupled with L-type Ca2+ channels and SK-type K+ channels. Further electrophysiological and immunochemical observations revealed that α-synuclein oligomers greater than 100 kDa were directly associated with calcium-binding protein 1, which is responsible for regulating IP3R gating. They also block Ca2+-dependent inactivation of IP3R, and trigger Ca2+-induced Ca2+ release from IP3R during multiple spikes. This aberrant machinery may result in intraneural Ca2+ dyshomeostasis and may be the molecular basis for the vulnerability of neurons in LBD brains.

Effects of 2'-3'-dihydroxy-4',6'-dimethoxychalcone derived from green perilla on auricle thickness in chronic contact dermatitis model mice.

Oxidative stress has been implicated in the pathogenesis of allergic contact dermatitis. The nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway, an in vivo antioxidant system, induces antioxidant enzymes. In our previous studies, we isolated 2',3'-dihydroxy-4',6'-dimethoxychalcone (DDC) from green perilla and identified it as a novel activator of the Nrf2-ARE pathway. We also discovered that it exerted cytoprotective effects against oxidative stress in PC12 cells. However, its effects on skin disease model animals in vivo remain unclear. In the present study, auricular thickness time-dependently increased with the repeated application of picryl chloride, and significant increases were observed from Day 2 in chronic contact hypersensitivity (cCHS) model mice. Histological changes, such as higher numbers of cells in the epidermis, were observed with increases in auricular thickness. The administration of DDC every two days from Day 6 suppressed the increases in auricular thickness and the number of scratching events in a dose-dependent manner. The expression levels of antioxidant enzymes increased in the mouse auricle 24 h after the administration of DDC. These results presume that DDC inhibits increases in auricular thickness in cCHS mice by up-regulating the expression of antioxidative enzymes through the activation of the Nrf2-ARE pathway.

Increased CCL6 expression in astrocytes and neuronal protection from neuron-astrocyte interactions.

Astrocytes have been reported to exhibit neuroprotective action via various chemokines. Reports of the chemokine CCL6 in central nervous system cells show expression in cultured microglia, but many unexplained effects on neurons and astrocytes remain. In this study, cultured cerebral cortical neurons, astrocytes, and a mixed culture system were constructed, and expression levels of CCL6 and its effects on glutamate neurotoxicity were examined. When neuron cultures and neuron-astrocyte mixed cultures were treated with glutamate, neuronal cell death was observed in both, but was induced by lower concentrations of glutamate in monocultured neurons. In addition, pretreatment of neuron cultures with conditioned media from neuron-astrocyte mixed cultures inhibited glutamate neurotoxicity. CCL6 expression was not observed in fluorescence activated cell sorting analyses of neuron and astrocyte cultures, but was observed in astrocytes from cocultures of neurons and astrocytes. Higher CCL6 concentrations were found in media from cocultures of neurons and astrocytes than in culture media from neuron cultures. Pretreatment of neuron cell cultures with CCL6 for 24 h also protected against glutamate neurotoxicity. This protective effect was suppressed by an antagonist of the chemokine receptor CCR1. Furthermore, glutamate neurotoxicity in mixed neuron and astrocyte cultures was enhanced by pretreatments with the CCR1 antagonist. Finally, cotreatments with the phosphatidylinositol-3 kinase (PI3K) inhibitor and CCL6 abolished the neuroprotective effects of CCL6. These data suggest that astrocytes protect neurons by activating CCR1 in neurons. Moreover, this neuroprotective action of astrocyte CCL6 is mediated by CCR1, and downstream by PI3K.

Protective Effect of Green Perilla-Derived Chalcone Derivative DDC on Amyloid ß Protein-Induced Neurotoxicity in Primary Cortical Neurons.

Amyloid ß protein (Aß) causes neurotoxicity and cognitive impairment in Alzheimer's disease (AD). Oxidative stress is closely related to the pathogenesis of AD. We have previously reported that 2',3'-dihydroxy-4',6'-dimethoxychalcone (DDC), a component of green perilla, enhances cellular resistance to oxidative damage through the activation of the nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway. Here, we investigated the effects of DDC on cortical neuronal death induced by Aß. When Aß and DDC had been preincubated for 3 h, the aggregation of Aß was significantly suppressed. In this condition, we found that DDC provided a neuroprotective action on Aß-induced cytotoxicity. Treatment with DDC for 24 h increased the expression of heme oxygenase-1 (HO-1), and this was controlled by the activation of the Nrf2-ARE pathway. However, DDC did not affect Aß-induced neuronal death under any of these conditions. These results suggest that DDC prevents the aggregation of Aß and inhibits neuronal death induced by Aß, and although it activates the Nrf2-ARE pathway, this mechanism is less involved its neuroprotective effect.

Protective Effects of 2',3'-Dihydroxy-4',6'-dimethoxychalcone Derived from Green Perilla Leaves against UV Radiation-Induced Cell Injury in Human Cultured Keratinocytes.

Skin exposure to UV rays causes the production of reactive oxygen species (ROS), and it is a major risk factor for various skin disorders and diseases. In particular, exposure to UV-A is a major cause of photoaging. We have previously isolated 2',3'-dihydroxy-4',6'-dimethoxychalcone (DDC) from green perilla leaves as an activator of the nuclear factor erythroid 2-related factor-2 (Nrf2)-antioxidant response element (ARE) and demonstrated the protective effects of DDC both in vitro and in vivo in PC12 cells and Parkinson's disease models, respectively. In this study, we used HaCaT cells to examine the effects of DDC on ROS production and cell damage induced by UV-A. Our results indicated that UV-A irradiation in HaCaT cells increased ROS production in an energy-dependent manner. In addition, cell viability decreased in an energy-dependent manner 24 h after UV-A irradiation. However, treatment with DDC 24 h prior to UV-A irradiation significantly suppressed UV-A radiation-induced ROS production. In addition, DDC showed cytoprotective effects when used 24 h before and after UV-A irradiation. Treatment with DDC for 24 h also increased the expression levels of heme oxygenase-1 (HO-1) in a concentration-dependent manner. Pretreatment with the HO-1 inhibitor followed by DDC treatment before UV-A irradiation for 24 h reduced ROS production and the cytoprotective effect. These results suggest that DDC increases the expression levels of HO-1 and protects HaCaT cells through the suppression of UV radiation-induced ROS production.

Donepezil modulates amyloid precursor protein endocytosis and reduction by up-regulation of SNX33 expression in primary cortical neurons.

Donepezil, a therapeutic drug for Alzheimer's disease, ameliorates cognitive dysfunction through selective inhibition of acetylcholinesterase. However, recent studies have also reported off-target effects of donepezil that likely contribute to its therapeutic effects. In this study, we investigated the (i) role of donepezil in amyloid precursor protein (APP) processing and (ii) involvement of sorting nexin protein 33 (SNX33), a member of the sorting nexin protein family, in this processing. Results showed that donepezil induces an increase in SNX33 expression in primary cortical neurons. The secretion of sAPPα in culture media increased, whereas the expression of full-length APP in the cell lysate remained unchanged. Exposure of cortical cultures to donepezil led to a decrease in amyloid ß (Aß) protein levels in a concentration- and time-dependent manner. This decrease was not affected by concomitant treatment with acetylcholine receptor antagonists. SNX33 knockdown by target-specific morpholino oligos inhibited the effects of donepezil. Donepezil treatment increased cell membrane surface expression of APP in SNX33 expression-dependent manner. These results suggested that donepezil decreases the level of Aß by increasing SNX33 expression and APP cleavage by α-secretase in cortical neurons.

[Establishment of a novel evaluation system for dopaminergic axonal outgrowth and its regulatory factor].

The nigrostriatal dopaminergic pathway is implicated with Parkinson's disease. Elucidation of this projection mechanism is not only important for considering developmental brain formation, but also contributes to the development of a therapy for regenerating the lost neural circuit. Although several axon guidance cues have been reported to induce dopaminergic axons from the substantia nigra to the striatum, the mechanisms by which the dopaminergic axons extend in the striatum remain unclear. An excellent culture system is necessary for studying the formation process of a neural circuit. Therefore, we tried to establish an in vitro model for the quantitative analysis of dopaminergic innervation of striatal neurons using primary dissociated cells. Mesencephalic cells prepared from rat embryos were seeded on the opposite side to striatal cells with the isolation wall in between. When the isolation wall was removed, the dopaminergic axons extended toward the striatal cell region and formed synapses with striatal neurons. The dopaminergic innervation of striatal neurons was suppressed by inhibiting integrin α5ß1 expressed on dopaminergic neurons. Furthermore, dopaminergic neurons overexpressing integrin α5 exhibited a longer neurite outgrowth on striatal cells than normal dopaminergic neurons did. Because this evaluation system using dissociated cell culture has relatively high throughput and is easy to be pharmacologically and genetically manipulated, it is considered to be a useful tool in the study of neural circuit formation. In addition, as a result, we found integrin α5ß1 as a molecule promoting striatal innervation by dopaminergic neuron, which is expected to contribute to regeneration of the nigrostriatal dopaminergic projection.

Inhibitory effect of the gut microbial linoleic acid metabolites, 10-oxo-trans-11-octadecenoic acid and 10-hydroxy-cis-12-octadecenoic acid, on BV-2 microglial cell activation.

10-oxo-trans-11-octadecenoic acid (KetoC) and 10-hydroxy-cis-12-octadecenoic acid (HYA) are long-chain fatty acids generated from linoleic acid by the gut lactic acid bacterium Lactobacillus plantarum. These fatty acids have been reported to have anti-inflammatory activity in the intestine. However, little is known about their effects in the brain. In this study, we aimed to investigate the effects of these fatty acids on lipopolysaccharide (LPS)-induced inflammatory processes in mouse microglial cells (BV-2 cells). KetoC and HYA inhibited LPS-induced nitric oxide (NO) production and suppressed the expression of inducible NO synthase in BV-2 cells. NO changes in these inhibitory effects were observed with AH7614, a G-protein coupled receptor 120 antagonist, or the peroxisome proliferator-activated receptors antagonists, GW6471 and GW9662. In addition, KetoC and HYA did not inhibit translocation of p65, a subunit of NF-κB, or IκB degradation. Similarly, no effect on p38 or JNK phosphorylation was observed. However, KetoC and HYA were found to inhibit ERK phosphorylation induced by LPS, suggesting that these fatty acids may exert their anti-inflammatory effects through the inhibition of ERK activation in microglial cells.

Neuroprotective effect of an Nrf2-ARE activator identified from a chemical library on dopaminergic neurons.

The nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway, which induces the production of antioxidant enzymes, is a possible therapeutic target for treating diseases related to oxidative stress. Nrf2 activators often exhibit cytotoxicity due to nonspecific electrophilic reactions with thiol groups. We screened a chemical library to explore Nrf2 activators with a wide safety margin. In at least in vitro experiments, TPNA10168, identified from the library, showed a higher efficacy in Nrf2 activation and a lower cytotoxicity than sulforaphane, a well-known Nrf2 activator. The present study demonstrated the protective effect of TPNA10168 against 6-hydroxydopamine-induced cytotoxicity. In PC12 cells, NAD(P)H:quinone oxidoreductase 1 was upregulated by TPNA10168 and participated in the protective effect. In primary mesencephalic cultures, heme oxygenase-1, upregulated by TPNA10168 in astrocytes, provided protection of dopaminergic neurons via a guanylate cyclase/protein kinase G signaling pathway via carbon monoxide. These results suggest that the compound identified from the chemical library may be suitable as a neuroprotective agent with the ability to induce antioxidant enzymes.

PE859, A Novel Curcumin Derivative, Inhibits Amyloid-ß and Tau Aggregation, and Ameliorates Cognitive Dysfunction in Senescence-Accelerated Mouse Prone 8.

Aggregation of amyloid-ß (Aß) and tau plays a crucial role in the onset and progression of Alzheimer's disease (AD). Therefore, the inhibition of Aß and tau aggregation may represent a potential therapeutic target for AD. Herein, we designed and synthesized both Aß and tau dual aggregation inhibitors based on the structure of curcumin and developed the novel curcumin derivative PE859. In this study, we investigated the inhibitory activity of PE859 on Aß aggregationin vitro and the therapeutic effects of PE859 on cognitive dysfunction via dual inhibition of Aß and tau aggregation in vivo. PE859 inhibited Aß aggregation in vitro and protected cultured cells from Aß-induced cytotoxicity. Furthermore, PE859 ameliorated cognitive dysfunction and reduced the amount of aggregated Aß and tau in brains of senescence-accelerated mouse prone 8 (SAMP8). These results warrant consideration of PE859 as a candidate drug for AD.

Inhibitory effect of donepezil on bradykinin-induced increase in the intracellular calcium concentration in cultured cortical astrocytes.

Donepezil is a potent and selective acetylcholinesterase inhibitor developed for the treatment of Alzheimer's disease. In the present study, we investigated the responses of astrocytes to bradykinin, an inflammatory mediator, and the effect of donepezil on these responses using cultured cortical astrocytes. Bradykinin induced a transient increase of intracellular calcium concentration ([Ca2+]i) in cultured astrocytes. Bradykinin-induced [Ca2+]i increase was inhibited by the exposure to thapsigargin, which depletes Ca2+ stores on endoplasmic reticulum, but not by the exclusion of extracellular Ca2+. Twenty four hours pretreatment of donepezil reduced the bradykinin-induced [Ca2+]i increase. This reduction was inhibited not only by mecamylamine, a nAChR antagonist, but also by PI3K and Akt inhibitors. In addition, donepezil inhibited bradykinin-induced increase of the intracellular reactive oxygen species level in astrocytes. These results suggest that donepezil inhibits the inflammatory response induced by bradykinin via nAChR and PI3K-Akt pathway in astrocytes.