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.

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.

[Donepezil Reduces Amyloid Precursor Protein Endocytosis by Resulting from Increase in the Expression of Sorting Nexin Protein 33]

Donepezil, the most widely used drug for the treatment of Alzheimer's disease (AD), is an acetylcholinesterase (AChE) inhibitor and is thought to improve cognition by stimulating cholinergic neurotransmission. However, no correlation has yet been established between the inhibitory role of AChE inhibitors and their therapeutic effects when used in AD patients. The cleavage pathway of amyloid precursor protein (APP) includes amyloidgenic (β, γ-cleavage) and non-amyloidgenic (α-cleavage) pathways. The intracellular transportation of APP is important in determining these cleavage pathways. It has been suggested that sorting nexin (SNX) family proteins regulates the intracellular transport of APP, thereby enhancing α-cleavage. In this study, we examined the effects of donepezil on SNX33 expression changes and APP processing in primary cultures of fetal rat cortical neurons. While donepezil treatment increased the levels of SNX33 expression and soluble APPα (sAPPα) in culture media, no changes were observed regarding full-length APP expression in the cell lysate. Donepezil also reduced the release of amyloid β (Aβ) into culture media in a concentration- and time-dependent manner. This reduction was not affected by acetylcholine receptor antagonists. The membrane surface expression of APP was elevated by donepezil. Furthermore, SNX knockdown by antisense morpholino oligos prevented the effects of donepezil. These results indicated that donepezil increased APP expression at the surface of the plasma membrane by decreasing APP endocytosis through upregulation of SNX33, suggesting donepezil might stimulate the non-amyloidogenic pathway. This new mechanism of action for the currently used anti-AD drug may provide a valuable basis for future drug discovery.

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.

Aromatherapy improves cognitive dysfunction in senescence-accelerated mouse prone 8 by reducing the level of amyloid beta and tau phosphorylation

Alzheimer’s disease (AD) is a progressive neurodegenerative disease and is known to be the most common cause of dementia. We previously described the benefits of aromatherapy on the cognitive function of patients with AD utilizing various aromatic essential oils; however, its mechanism of action remains poorly understood. Consequently, in the present study, this mechanism was thoroughly evaluated employing a dementia mice model, specifically the senescence-accelerated mouse prone 8. The mice were exposed to a mixture of lemon and rosemary oil at nighttime as well as to a mixture of lavender and orange oil in the daytime for 2 months. The cognitive function of the mice was assessed before and after treatment with the aromatic essential oils using the Y-maze test. Moreover, the brain levels of amyloid beta (Aβ), abnormally phosphorylated tau, and brain-derived neurotrophic factor (BDNF) were measured following treatment. The benefits of aromatherapy on the cognitive function in mice were confirmed. It was also established that the brain levels of Aβ and abnormally phosphorylated tau were considerably lower in the aromatherapy group, while the levels of BDNF were marginally higher. These results suggest that aromatherapy employing these aromatic essential oils is beneficial for the prevention and treatment of AD.

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.

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.

Potential protective effect of highly bioavailable curcumin on an oxidative stress model induced by microinjection of sodium nitroprusside in mice brain

The protective effects of conventional curcumin or highly bioavailable curcumin, Theracurmin^®, against oxidative stress is investigated using our in vivo oxidative stress model.

Staurosporine induces dopaminergic neurite outgrowth through AMP-activated protein kinase/mammalian target of rapamycin signaling pathway

Axonal degeneration of dopaminergic neurons is one of the pathological features in the early stages of Parkinson disease. Promotion of axonal outgrowth of the remaining dopaminergic neurons leads to the recovery of the nigrostriatal pathway. Staurosporine (STS), a wide-spectrum kinase inhibitor, induces neurite outgrowth in various cell types, although its mechanism of action remains elusive. In this study, we analyzed which protein kinase is involved in STS-induced neurite outgrowth. We have previously established the method to measure the length of dopaminergic neurites that extend from a mesencephalic cell region, which is formed on a coverslip by an isolation wall. By means of this method, we clarified that STS treatment causes dopaminergic axonal outgrowth in mesencephalic primary cultures. Among the specific protein kinase inhibitors we tested, compound C (C.C), an AMP-activated protein kinase (AMPK) inhibitor, promoted dopaminergic neurite outgrowth. STS as well as C.C elevated the phosphorylation level of 70-kDa ribosomal protein S6 kinase, a downstream target of mammalian target of rapamycin (mTOR) signaling pathway. The STS- and C.C-induced dopaminergic neurite outgrowth was suppressed by rapamycin, an mTOR inhibitor. Furthermore, the application of C.C rescued 1-methyl-4-phenylpyridinium ion (MPP(+))-induced dopaminergic neurite degeneration. These results suggest that STS induces dopaminergic axonal outgrowth through mTOR signaling pathway activation as a consequence of AMPK inhibition.

Protective effect of luteolin on an oxidative-stress model induced by microinjection of sodium nitroprusside in mice

Accumulating lines of evidence showed that luteolin, a polyphenolic compound, has potent neuroprotective effects. The purpose of this study was to examine whether luteolin can protect against sodium nitroprusside (SNP)-induced oxidative damage in mouse brain. Intrastriatal co-injection of luteolin (3 - 30 nmol) with SNP (10 nmol) dose-dependently protected against brain damage and motor dysfunction. Oral administrations of luteolin (600 - 1200 mg/kg) dose-dependently protected against brain damage and motor dysfunction induced by striatal injection of SNP. Furthermore, luteolin (30 - 100 μM) concentration dependently protected against Fe(2+)-induced lipid peroxidation in mouse brain homogenate. Luteolin (1 - 100 μg/ml) showed potent DPPH radical scavenging ability, when compared with ascorbic acid and glutathione. Finally, a ferrozine assay showed that luteolin (30 - 100 μg/ml) has Fe(2+)-chelating ability, but this was weaker than that of ethylenediaminetetraacetic acid. These results suggest that intrastriatal or oral administration of luteolin protected mice brain from SNP-induced oxidative damage by scavenging and chelating effects.

Isolation, identification, and biological evaluation of Nrf2-ARE activator from the leaves of green perilla (Perilla frutescens var. crispa f. viridis)

The nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway is a cellular defense system against oxidative stress. Activation of this pathway increases expression of antioxidant enzymes. Epidemiological studies have demonstrated that the consumption of fruits and vegetables is associated with reduced risk of contracting a variety of human diseases. The aim of this study is to find Nrf2-ARE activators in dietary fruits and vegetables. We first attempted to compare the potency of ARE activation in six fruit and six vegetables extracts. Green perilla (Perilla frutescens var. crispa f. viridis) extract exhibited high ARE activity. We isolated the active fraction from green perilla extract through bioactivity-guided fractionation. Based on nuclear magnetic resonance and mass spectrometric analysis, the active ingredient responsible for the ARE activity was identified as 2',3'-dihydroxy-4',6'-dimethoxychalcone (DDC). DDC induced the expression of antioxidant enzymes, such as γ-glutamylcysteine synthetase (γ-GCS), NAD(P)H: quinone oxidoreductase-1 (NQO1), and heme oxygenase-1. DDC inhibited the formation of intracellular reactive oxygen species and the cytotoxicity induced by 6-hydroxydopamine. Inhibition of the p38 mitogen-activated protein kinase pathway abolished ARE activation, the induction of γ-GCS and NQO1, and the cytoprotective effect brought about by DDC. Thus, this study demonstrated that DDC contained in green perilla enhanced cellular resistance to oxidative damage through activation of the Nrf2-ARE pathway.

Glutathione biosynthesis via activation of the nuclear factor E2-related factor 2 (Nrf2)--antioxidant-response element (ARE) pathway is essential for neuroprotective effects of sulforaphane and 6-(methylsulfinyl) hexyl isothiocyanate

Oxidative stress plays pivotal roles in aging, neurodegenerative disease, and pathological conditions such as ischemia. We investigated the effect of sulforaphane and 6-(methysulfinyl) hexyl isothiocyanate (6-HITC), a naturally occurring isothiocyanate, on oxidative stress-induced cytotoxicity using primary neuronal cultures of rat striatum. Pretreatment with sulforaphane and 6-HITC significantly protected against H(2)O(2)- and paraquat-induced cytotoxicity in a concentration-dependent manner. Sulforaphane and 6-HITC induced the translocation of nuclear factor E2-related factor 2 (Nrf2) into the nucleus and increased the expression of γ-glutamylcysteine synthetase (γ-GCS), a rate-limiting enzyme in glutathione synthesis, and the intracellular glutathione content. Treatment with reduced glutathione (GSH) and N-acetyl-L-cysteine, a substance for glutathione synthesis, significantly prevented the cytotoxicity induced by H(2)O(2) and paraquat. Moreover, exposure to L-buthionine-sulfoximine, an irreversible inhibitor of γ-GCS, suppressed the protective effects of sulforaphane and 6-HITC. In contrast, sulforaphane and 6-HITC increased heme oxygenase-1 (HO-1) expression in neurons. However, zinc-protophorphyrin IX, a competitive inhibitor of HO-1, did not influence the protective effects of sulforaphane and 6-HITC. These results suggest that sulforaphane and 6-HITC prevent oxidative stress-induced cytotoxicity in rat striatal cultures by raising the intracellular glutathione content via an increase in γ-GCS expression induced by the activation of the Nrf2-antioxidant response element pathway.

Mitogen-activated protein kinases support survival of activated microglia that mediate thrombin-induced striatal injury in organotypic slice culture

Intracerebral hemorrhage-associated tissue damage is triggered by blood-derived serine proteases such as thrombin. In addition, our previous studies have suggested that mitogen-activated protein (MAP) kinases contribute to intracerebral hemorrhage- and thrombin-induced striatal tissue damage in vivo. Here we addressed the mechanisms of MAP kinase involvement in thrombin cytotoxicity in rat corticostriatal slice culture, focusing on striatal tissue damage. Thrombin induced apoptotic nuclear condensation and fragmentation in striatal cells, which was suppressed by DEVD-CHO, a caspase-3 inhibitor. DEVD-CHO also prevented shrinkage of the striatal tissue induced by thrombin. Phagocytotic activity may be involved in tissue deterioration, because a phagocytosis inhibitor (cytochalasin D) and an inhibitor of phagocytosis of apoptotic cells (O-phospho-L-serine) suppressed shrinkage of the striatal tissue. OX42 immunostaining revealed that apoptosis-like microglial cell death was induced only when thrombin treatment was combined with application of inhibitors of MAP kinase/extracellular signal-regulated kinase kinase (PD98059), p38 MAP kinase (SB203580), or c-Jun N-terminal kinase (SP600125). Thrombin-induced increase in the number of microglia was also prevented by these inhibitors of MAP kinase pathways. We also found that thrombin-induced production of tumor necrosis factor (TNF)-alpha was inhibited by PD98059, SB203580, and SP600125. Finally, thrombin-induced neuronal apoptosis and shrinkage of the striatal tissue were significantly inhibited by anti-TNF-alpha neutralizing antibody. These results suggest that MAP kinases contribute to thrombin-induced striatal damage by supporting survival of activated microglia, which induce neuron death by producing TNF-alpha and cause tissue shrinkage by phagocytosing apoptotic cells.

Elevation of heme oxygenase-1 by proteasome inhibition affords dopaminergic neuroprotection

Postmortem studies have shown that heme oxygenase-1 (HO-1) immunoreactivity is increased in patients with Parkinson disease. HO-1 expression is highly upregulated by a variety of stress. Since the proteasome activity is decreased in patients with Parkinson disease, we investigated whether proteasome activity regulates HO-1 content. MG-132, a proteasome inhibitor, increased the amount of HO-1 protein mainly in astrocytes of primary mesencephalic cultures. Quantitative RT-PCR analysis revealed that lactacystin upregulated HO-1 mRNA expression. Proteasome inhibition with MG132 also increased the cytomegalovirus promoter-driven expression of Flag-HO-1 protein and resulted in an accumulation of ubiquitinated Flag-HO-1 in Flag-HO-1-overexpressing PC12 cells. In addition, a cycloheximide chase assay demonstrated that the degradation of Flag-HO-1 protein was slowed by MG-132. Next, the function of HO-1 which was upregulated by proteasome inhibitors was examined. Proteasome inhibitors protected dopaminergic neurons from 6-hydroxydopamine (6-OHDA)-induced toxicity and this neuroprotection was abrogated by co-treatment with zinc protoporphyrin IX, a HO-1 inhibitor. Furthermore, 6-OHDA-induced toxicity was blocked by bilirubin and carbon monoxide, products of the HO-1-catalyzed degradation of heme. These results suggest that mesencephalic HO-1 protein level is regulated by proteasome activity and the elevation by proteasome inhibition affords neuroprotection.

Reconstruction and quantitative evaluation of dopaminergic innervation of striatal neurons in dissociated primary cultures

Repairing the nigrostriatal pathway is expected to become a future treatment strategy for Parkinson disease. Our aim is to establish an in vitro model for the quantitative analysis of the nigrostriatal projections of dopaminergic neurons using primary dissociated neruons. To form the mesencephalic cell region, mesencephalic cells derived from rat embryos were plated within an isolation wall, which was removed after cell adhesion to the coverslip. After incubation for 11 days, the dopaminergic neurites extending to the outside of the mesencephalic cell region were mainly axons. Treatment with glial cell line-derived neurotrophic factor for 11 days significantly promoted the outgrowth of dopaminergic axons from the mesencephalic cell region in a concentration-dependent manner. When striatal cells were plated outside the mesencephalic cell region, dopaminergic neurites were remarkably extended to the striatal cell region. Moreover, immunocytochemistry for tyrosine hydroxylase and synaptophysin revealed that dopaminergic axons formed synapses with striatal neurons. By contrast, spinal cells did not increase dopaminergic neurite outgrowth. These results indicate that the present method is valuable for evaluating nigrostriatal projections in vitro.

Protective effect of aripiprazole against glutamate cytotoxicity in dopaminergic neurons of rat mesencephalic cultures

Aripiprazole, a dopamine D(2) receptor partial agonist, is used to treat schizophrenia. Although aripiprazole has been reported to protect non-dopaminergic neurons, its effect on dopaminergic neurons has yet to be investigated. In the present study, we examined whether aripiprazole protected dopaminergic neurons against glutamate-induced cytotoxicity in rat mesencephalic cultures. Pretreatment with aripiprazole protected dopaminergic neurons in a concentration-dependent manner. The neuroprotective effect was not attenuated by sulpiride, a dopamine D(2) receptor antagonist, suggesting that the effect is independent of dopamine D(2) receptors. Aripiprazole reduced intracellular dopamine content in a concentration-dependent manner. In addition, its neuroprotective effect was partially inhibited when dopamine was added. These results suggest that aripiprazole protects dopaminergic neurons against glutamate cytotoxicity partly by reducing intracellular dopamine content.

Heme oxygenase-1 contributes to pathology associated with thrombin-induced striatal and cortical injury in organotypic slice culture

The blood coagulation factor thrombin that leaks from ruptured vessels initiates brain tissue damage after intracerebral hemorrhage. We have recently shown that mitogen-activated protein kinases (MAPKs) activated by thrombin exacerbate hemorrhagic brain injury via supporting survival of neuropathic microglia. Here, we investigated whether induction of heme oxygenase (HO)-1 is involved in these events. Zinc protoporphyrin IX (ZnPP IX), a HO-1 inhibitor, attenuated thrombin-induced injury of cortical cells in a concentration-dependent manner (0.3-3 microM) and tended to inhibit shrinkage of the striatal tissue at 0.3 microM. HO-1 expression was induced by thrombin in microglia and astrocytes in both the cortex and the striatum. The increase of HO-1 protein was suppressed by a p38 MAPK inhibitor SB203580, and early activation of p38 MAPK after thrombin treatment was observed in neurons and microglia in the striatum. Notably, concomitant application of a low concentration (0.3 microM) of ZnPP IX with thrombin induced apoptotic cell death in striatal microglia and significantly decreased the number of activated microglia in the striatal region. On the other hand, a carbon monoxide releaser reversed the protective effect of ZnPP IX on thrombin-induced injury of cortical cells. Overall, these results suggest that p38 MAPK-dependent induction of HO-1 supports survival of striatal microglia during thrombin insults. Thrombin-induced cortical injury may be also regulated by the expression of HO-1 and the resultant production of heme degradation products such as carbon monoxide.

Mechanisms of chronic nicotine treatment-induced enhancement of the sensitivity of cortical neurons to the neuroprotective effect of donepezil in cortical neurons

We have previously shown that chronic donepezil treatment induces nicotinic acetylcholine receptor up-regulation and enhances the sensitivity of the neurons to the neuroprotective effect of donepezil. Further analyses revealed that the nicotinic receptor is involved in this enhancement. In this study, we examined whether nicotinic receptor stimulation is sufficient to make neurons more sensitive to donepezil. We treated primary cultures of rat cortical neurons with nicotine and confirmed that chronic nicotine treatment induced nicotinic receptor up-regulation and made the neurons more sensitive to the neuroprotective effects of donepezil. Analyses with receptor antagonists and kinase inhibitors revealed that the effects of chronic nicotine treatment are mediated by nicotinic receptors and their downstream effectors including phosphatidylinositol 3-kinase. In contrast to chronic donepezil treatment that enhanced the level of nicotine-induced Ca(2+) influx, chronic nicotine treatment did not significantly alter the level of Ca(2+) influx.

Acetylcholine synthesis and release in NIH3T3 cells coexpressing the high-affinity choline transporter and choline acetyltransferase

Acetylcholine (ACh) is known to be a key neurotransmitter in the central and peripheral nervous systems, but it is also produced in a variety of non-neuronal tissues and cells, including lymphocytes, placenta, amniotic membrane, vascular endothelial cells, keratinocytes, and epithelial cells in the digestive and respiratory tracts. To investigate contribution made by the high-affinity choline transporter (CHT1) to ACh synthesis in both cholinergic neurons and nonneuronal cells, we transfected rat CHT1 cDNA into NIH3T3ChAT cells, a mouse fibroblast line expressing mouse choline acetyltransferase (ChAT), to establish the NIH3T3ChAT 112-1 cell line, which stably expresses both CHT1 and ChAT. NIH3T3ChAT 112-1 cells showed increased binding of the CHT1 inhibitor [(3)H]hemicholinium-3 (HC-3) and greater [(3)H]choline uptake and ACh synthesis than NIH3T3ChAT 103-1 cells, a CHT1-negative control cell line. HC-3 significantly inhibited ACh synthesis in NIH3T3ChAT 112-1 cells but did not affect synthesis in NIH3T3ChAT 103-1 cells. ACh synthesis in NIH3T3ChAT 112-1 cells was also reduced by amiloride, an inhibitor of organic cation transporters (OCTs) involved in low-affinity choline uptake, and by procaine and lidocaine, two local anesthetics that inhibit plasma membrane phospholipid metabolism. These results suggest that CHT1 plays a key role in ACh synthesis in NIH3T3ChAT 112-1 cells and that choline taken up by OCTs or derived from the plasma membrane is also utilized for ACh synthesis in both cholinergic neurons and nonneuronal cholinergic cells, such as lymphocytes.

Serofendic acid promotes stellation induced by cAMP and cGMP analogs in cultured cortical astrocytes

We investigated the effect of serofendic acid, a neuroprotective substance derived from fetal calf serum, on the morphological changes in cultured cortical astrocytes. Cultured astrocytes developed a stellate morphology with several processes following exposure to dibutylyl cAMP (dbcAMP), a membrane-permeable cAMP analog; 8-Br-cGMP, a membrane-permeable cGMP analog; or phorbol-12-myristate-13-acetate (PMA), a protein kinase C activator. Serofendic acid significantly accelerated the stellation induced by dbcAMP- and 8-Br-cGMP. In contrast, the PMA-induced stellation was not affected by serofendic acid. Next, we attempted to elucidate the mechanism underlying the dbcAMP-induced stellation and explore the site of action of serofendic acid. Both the stellation induced by dbcAMP and the promotional effect of serofendic acid were partially inhibited by KT5720, a specific protein kinase A (PKA) inhibitor. Furthermore, serofendic acid failed to facilitate the stellation induced by Y-27632, an inhibitor of Rho-associated kinase (ROCK). These results indicate that serofendic acid promotes dbcAMP- and 8-Br-cGMP-induced stellation and the promotional effect on dbcAMP-induced stellation is mediated at least partly by the regulation of PKA activity and not by controlling ROCK activity.

Dibutyryl cyclic AMP induces differentiation of human neuroblastoma SH-SY5Y cells into a noradrenergic phenotype

Dibutyryl cyclic AMP (dbcAMP) and retinoic acid (RA) have been demonstrated to be the inducers of morphological differentiation in SH-SY5Y cells, a human catecholaminergic neuroblastoma cell line. However, it remains unclear whether morphologically differentiated SH-SY5Y cells by these compounds acquire catecholaminergic properties. We focused on the alteration of tyrosine hydroxylase (TH) expression and intracellular content of noradrenaline (NA) as the indicators of functional differentiation. Three days treatment with dbcAMP (1mM) and RA (10microM) induced morphological changes and an increase of TH-positive cells using immunocytochemical analysis in SH-SY5Y cells. The percentage of TH-expressing cells in dbcAMP (1mM) treatment was larger than that in RA (10microM) treatment. In addition, dbcAMP increased intracellular NA content, whereas RA did not. The dbcAMP-induced increase in TH-expressing cells is partially inhibited by KT5720, a protein kinase A (PKA) inhibitor. We also investigated the effect of butyrate on SH-SY5Y cells, because dbcAMP is enzymatically degraded by intracellular esterase, thereby resulting in the formation of butyrate. Butyrate induced the increase of NA content at lower concentrations than dbcAMP, although the increase in TH-expressing cells by butyrate was smaller than that by dbcAMP. The dbcAMP (1mM)- and butyrate (0.3mM)-induced increase in NA content was completely suppressed by alpha-methyl-p-tyrosine (1mM), an inhibitor of TH. These results suggest that dbcAMP induces differentiation into the noradrenergic phenotype through both PKA activation and butyrate.

Mechanisms of alpha7-nicotinic receptor up-regulation and sensitization to donepezil induced by chronic donepezil treatment

alpha7-nicotinic acetylcholine receptors are one of the most abundant subtypes of nicotinic receptors in the brain and have been shown to be involved in the neuroprotective effect of donepezil. Recently, we showed that in primary culture of rat cortical neurons, chronic donepezil treatment (10 muM, 4 days) (1) induces the up-regulation of alpha7-nicotinic receptors, (2) enhances the nicotine-induced increase in [Ca(2+)](i) and (3) enhances the sensitivity to the neuroprotective effect of donepezil. Here we demonstrate the involvement of alpha7-nicotinic receptors in these three effects. Concomitant treatment with nicotinic receptor antagonist inhibited the up-regulation of alpha7-nicotinic receptor, enhancement of the increase in [Ca(2+)](i) induced by nicotine, and enhancement of sensitivity to the neuroprotective effect of donepezil. Next, using inhibitors of phosphatidylinositol 3-kinase and mitogen-activated protein kinase signaling pathways, we demonstrate the involvement of these pathways in the up-regulation of alpha7-nicotinic receptors and in making the neurons more sensitive to the neuroprotective effects of donepezil. Concomitant chronic donepezil treatment with inhibitors of phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways inhibited nicotinic receptor up-regulation and enhancement of the response to nicotine, and enhanced the sensitivity to donepezil. This study increases understanding of the less-studied mechanism of chronic donepezil treatment-induced nicotinic receptor up-regulation and increased sensitivity to donepezil.

Basic and clinical aspects of non-neuronal acetylcholine: expression of an independent, non-neuronal cholinergic system in lymphocytes and its clinical significance in immunotherapy

Lymphocytes possess all the components required to constitute an independent, non-neuronal cholinergic system. These include acetylcholine (ACh); choline acetyltransferase (ChAT), its synthesizing enzyme; and both muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively). ACh modifies T and B cell function via both mAChR- and nAChR-mediated pathways. Stimulation of lymphocytes with the T cell activator phytohemagglutinin, protein kinase C activator phorbol ester, or cell surface molecules enhances the synthesis and release of ACh and up-regulates ChAT and/or M(5) mAChR gene expression. Furthermore, animal models of immune disorders exhibit abnormal lymphocytic cholinergic activity. The cholesterol-lowering drug simvastatin attenuates the lymphocytic cholinergic activity of T cells by inhibiting LFA-1 signaling in a manner independent of its cholesterol-lowering activity. This suggests that simvastatin exerts its immunosuppressive effects in part by modifying lymphocytic cholinergic activity. Nicotine, an active ingredient of tobacco, ameliorates ulcerative colitis but exacerbates Crohn's disease. Expression of mRNAs encoding the nAChR alpha7 and alpha5 subunits are significantly diminished in peripheral mononuclear leukocytes from smokers, as compared with those from nonsmokers. In addition, long-term exposure of lymphocytes to nicotine reduces intracellular Ca(2+) signaling via alpha7 nAChR-mediated pathways. In fact, studies of humoral antibody production in M(1)/M(5) mAChR-deficient and alpha7 nAChR-deficient animals revealed the role of lymphocytic cholinergic activity in the regulation of immune function. These results provide clues to understanding the mechanisms underlying immune system regulation and could serve as the basis for the development of new immunomodulatory drugs.

Roles played by lymphocyte function-associated antigen-1 in the regulation of lymphocytic cholinergic activity

Lymphocytes possess the essential components of a cholinergic system, including acetylcholine (ACh); choline acetyltransferase (ChAT), its synthesizing enzyme; and both muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively). Stimulation of lymphocytes with phytohemagglutinin, which activates T cells via the T cell receptor/CD3 complex, enhances the synthesis and release of ACh and up-regulates expression of ChAT and M(5) mAChR mRNAs. In addition, activation of protein kinase C and increases in intracellular cAMP also enhance cholinergic activity in T cells, and lymphocyte function associated antigen-1 (LFA-1; CD11a/CD18) is an important mediator of leukocyte migration and T cell activation. Anti-CD11a monoclonal antibody (mAb) as well as antithymocyte globulin containing antibodies against CD2, CD7 and CD11a all increase ChAT activity, ACh synthesis and release, and expression of ChAT and M(5) mAChR mRNAs in T cells. The cholesterol-lowering drug simvastatin inhibits LFA-1 signaling by binding to an allosteric site on CD11a (LFA-1 alpha chain), which leads to immunomodulation. We found that simvastatin abolishes anti-CD11a mAb-induced increases in lymphocytic cholinergic activity in a manner independent of its cholesterol-lowering activity. Collectively then, these results indicate that LFA-1 contributes to the regulation of lymphocytic cholinergic activity via CD11a-mediated pathways and suggest that simvastatin exerts its immunosuppressive effects in part via modification of lymphocytic cholinergic activity.

Neuroprotective effects of galanthamine and tacrine against glutamate neurotoxicity

We examined the mechanisms of the neuroprotective effects of two central-type acetylcholinesterase inhibitors, galanthamine and tacrine, on nitric oxide-mediated glutamate neurotoxicity using primary cultures from the cerebral cortex of fetal rats. Galanthamine and tacrine showed prominent protective effects against glutamate neurotoxicity. Mecamylamine, a nicotinic acetylcholine receptor antagonist, but not scopolamine, a muscarinic acetylcholine receptor antagonist, inhibited the protective effects of these inhibitors on glutamate neurotoxicity. Furthermore, dihydro-beta-erythroidine, an alpha4-nicotinic receptor antagonist, and methyllycaconitine, an alpha7-nicotinic receptor antagonist, inhibited the neuroprotective effects of galanthamine but not tacrine. Next, we investigated the site of action where galanthamine and tacrine prevent glutamate neurotoxicity. Both these acetylcholinesterase inhibitors prevented glutamate- and ionomycin-induced neurotoxicity, but only tacrine prevented S-nitrosocysteine-induced neurotoxicity. These results suggest that galanthamine and tacrine protect cortical neurons from glutamate neurotoxicity via different mechanisms.

Acetylcholinesterase inhibitors used in treatment of Alzheimer's disease prevent glutamate neurotoxicity via nicotinic acetylcholine receptors and phosphatidylinositol 3-kinase cascade

We show here that donepezil, galanathamine and tacrine, therapeutic acetylcholinesterase inhibitors currently being used for treatment of Alzheimer's disease, protect neuronal cells in a time- and concentration-dependent manner from glutamate neurotoxicity that involves apoptosis. The neuroprotective effects were antagonized by mecamylamine, an inhibitor of nicotinic acetylcholine receptors (nAChRs). Dihydro-beta-erythroidine and methyllycaconitine, antagonists for alpha4-nAChR and alpha7-nAChR, respectively, antagonized the protective effect of donepezil and galanthamine, but not that of tacrine. Previous reports suggest the involvement of the phosphatidylinositol 3-kinase (PI3K)-Akt pathway in the nicotine-induced neuroprotection. Inhibitors for a non-receptor type tyrosine kinase, Fyn, and janus-activated kinase 2, suppressed the neuroprotective effect of donepezil and galanthamine, but not that of tacrine. Furthermore, LY294002, a PI3K inhibitor, also suppressed the neuroprotective effect of donepezil and galanthamine, but not that of tacrine. The phosphorylation of Akt, an effector of PI3K, and the expression level of Bcl-2, an anti-apoptotic protein, increased with donepezil and galanthamine treatment, but not with tacrine treatment. These results suggest that donepezil and galanthamine prevent glutamate neurotoxicity through alpha4- and alpha7-nAChRs, followed by the PI3K-Akt pathway, and that tacrine protects neuronal cells through a different pathway.