Norepinephrine provides short-term neuroprotection against Aβ1–42 by reducing oxidative stress independent of Nrf2 activation

Pathophysiological evidence correlating locus ceruleus neuron loss with increased Alzheimer's disease pathology suggests that norepinephrine (NE) is neuroprotective. Here, we evaluated the effects of NE on amyloid-β (Aβ)1-42–induced neurotoxicity and determined how NE exerts its actions in human SK-N-SH neurons. NE protected SK-N-SH cells against Aβ1-42–induced neurotoxicity only after a 4-hour treatment. The ability of NE to reduce Aβ1-42–induced neurotoxicity was independent of the adrenoceptor signaling pathway. Notably, NE downregulated Aβ1-42–mediated increases in intracellular reactive oxygen species (ROS) production. However, NE did not affect Aβ1-42–induced activation of the nuclear factor erythroid 2–related factor 2 (Nrf2) redox signaling pathway, known to be involved in oxidative stress. Among the antioxidants tested, N-acetyl cysteine and glutathione, which are not only ROS scavengers but also thiol-reducing agents, mimicked the protective effects of NE. Consistently, Kelch-like ECH-associating protein 1 inhibitors, which activated the Nrf2 pathway, failed to decrease Aβ1-42–induced ROS generation and elicited no protection against Aβ1–42. Taken together, these findings suggest that NE could exert neuroprotective function against Aβ1–42 via redox cycling and reduction of intracellular oxidative stress regardless of downstream activation of the Nrf2 pathway.     

HgCl(2)-induced human lymphocyte activation in vitro: a superantigenic mechanism?

Mercuric chloride (HgCl(2)) has been proposed to be a mitogen for human blood lymphocytes in vitro. In our previous study, we demonstrated that HgCl(2) preferentially stimulates the CD4+ T cell subset to blast transformation and DNA synthesis and that the reaction is dependent on CD14+ accessory cells. In order to characterise the responding cells further and to elucidate the mechanism of T cell activation, the T cell receptor (TCR) Vbeta chain expression of the blast-transformed cells was analysed by monoclonal antibodies and flow cytometry. The 22 TCR-Vbeta-specific antibodies used were found to react with 55-80% of the naive CD4+ and CD8+ blood T cells from the different donors. Six to 18% of the lymphocytes, mainly CD4+ T cells, were blast transformed after addition of HgCl(2). The distribution of the lymphoblasts carrying certain TCR Vbeta chains were skewed, and 15-40% expressed the TCR Vbeta2 chain. Furthermore, if cells were pretreated for 5 days with HgCl(2), whereafter recombinant interleukin-2 in fresh medium was added, the TCR Vbeta7+ T cell subset was also stimulated to blast transformation. The superantigen staphyloccal enterotoxin B, as a control, induced blast transformation in 10-26% of the lymphocytes, mainly CD4+ T cells, which were, as expected, positive for Vbeta3, Vbeta12, Vbeta14 or Vbeta17. We conclude that HgCl(2) has characteristics of a superantigen, activating the human lymphocytes in a Vbeta-chain-selective manner in vitro.     

GSK-3β activation mediates Nogo-66-induced inhibition of neurite outgrowth in N2a cells

The axons of the adult mammalian brain and spinal cord fail to regenerate after injury, and it has been suggested that Nogo-66 could prevent CNS axon repair. However, the mechanism of Nogo-66 inhibiting neurite outgrowth remains unknown. Our previous results indicated that protein kinase B (PKB) is involved in the inhibition of the neurite outgrowth by Nogo-66. Glycogen synthase kinase-3β (GSK-3β) is implicated in many processes in the nervous system, including differentiation, specification, polarity, plasticity and axon growth. In addition, GSK-3β is one of the most important molecules downstream of PKB. In the present study, we report on the role of GSK-3β signaling on Nogo-66-treated mouse neuroblastoma N2a cells. Nogo-66 reduced the phosphorylation of GSK-3β at Ser9 in N2a cells. In contrast, pretreatment with SB216763, a specific inhibitor of GSK-3β, resulted in an amelioration of neurite outgrowth by Nogo-66, compared with the Nogo-66 alone group (P < 0.05). Moreover, we performed RNA interference experiments to knock down GSK-3β expression levels in N2a cells via transient transfection of shRNA plasmids. The inhibition of neurite outgrowth by Nogo-66 was subdued in shRNA cells, compared to the non-RNAi cells (P < 0.05). Taken together, these data suggest that GSK-3β is involved in the inhibition by Nogo-66 of neurite outgrowth in N2a cells.     

Toll-like receptor (TLR)-4 mediates anti-β2GPI/β2GPI-induced tissue factor expression in THP-1 cells

Our previous study demonstrated that annexin A2 (ANX2) on cell surface could function as a mediator and stimulate tissue factor (TF) expression of monocytes by anti‐β₂‐glycoprotein I/β₂‐glycoprotein I complex (anti‐β₂GPI/β₂GPI). However, ANX2 is not a transmembrane protein and lacks the intracellular signal transduction pathway. Growing evidence suggests that Toll‐like receptor 4 (TLR‐4) might act as an ‘adaptor’ for intracellular signal transduction in anti‐β₂GPI/β₂GPI‐induced TF expressing cells. In the current study, we investigated the roles of TLR‐4 and its related molecules, myeloid differentiation protein 2 (MD‐2) and myeloid differentiation factor 88 (MyD88), in anti‐β₂GPI/β₂GPI‐induced TF expressing human monocytic‐derived THP‐1 (human acute monocytic leukaemia) cells. The relationship of TLR‐4 and ANX2 in this process was also explored. Along with TF, expression of TLR‐4, MD‐2 and MyD88 in THP‐1 cells increased significantly when treated by anti‐β₂GPI (10 µg/ml)/β₂GPI (100 µg/ml) complex. The addition of paclitaxel, which competes with the MD‐2 ligand, could inhibit the effects of anti‐β₂GPI/β₂GPI on TLR‐4, MD‐2, MyD88 and TF expression. Both ANX2 and TLR‐4 in THP‐1 cell lysates could bind to β₂GPI that had been conjugated to a column (β₂GPI‐Affi‐Gel). Furthermore, TLR‐4, MD‐2, MyD88 and TF expression was remarkably diminished in THP‐1 cells infected with ANX2‐specific RNA interference (RNAi) lentivirus (LV‐RNAi‐ANX2), in spite of treatment with a similar concentration of anti‐β₂GPI/β₂GPI complex. These results indicate that TLR‐4 and its signal transduction pathway contribute to anti‐β₂GPI/β₂GPI‐induced TF expression in THP‐1 cells, and the effects of TLR‐4 with ANX2 are tightly co‐operative.     

β-Caryophyllene inhibits dextran sulfate sodium-induced colitis in mice through CB2 receptor activation and PPARγ pathway

Cannabinoid receptor 2 (CB2) activation is suggested to trigger the peroxisome proliferator-activated receptor-γ (PPARγ) pathway, and agonists of both receptors improve colitis. Recently, the plant metabolite (E)-β-caryophyllene (BCP) was shown to bind to and activate CB2. In this study, we examined the anti-inflammatory effect of BCP in dextran sulfate sodium (DSS)-induced colitis and analyzed whether this effect was mediated by CB2 and PPARγ. Oral treatment with BCP reduced disease activity, colonic macro- and microscopic damage, myeloperoxidase and N-acetylglucosaminidase activities, and levels and mRNA expression of colonic tumor necrosis factor-α, IL-1β, interferon-γ, and keratinocyte-derived chemokine. BCP treatment also inhibited the activation of extracellular signal-regulated kinase 1/2, nuclear factor κB, IκB-kinase α/β, cAMP response element binding and the expression of caspase-3 and Ki-67. Moreover, BCP enhanced IL-4 levels and forkhead box P3 mRNA expression in the mouse colon and reduced cytokine levels (tumor necrosis factor-α, keratinocyte-derived chemokine, and macrophage-inflammatory protein-2) in a culture of macrophages stimulated with lipopolysaccharide. The use of the CB2 antagonist AM630 or the PPARγ antagonist GW9662 significantly reversed the protective effect of BCP. Confirming our results, AM630 reversed the beneficial effect of BCP on pro-inflammatory cytokine expression in IEC-6 cells. These results demonstrate that the anti-inflammatory effect of BCP involves CB2 and the PPARγ pathway and suggest BCP as a possible therapy for the treatment of inflammatory bowel disease.     

Huperzine A protects neural stem cells against Aβ-induced apoptosis in a neural stem cells and microglia co-culture system

Objectives: This study aims to explore whether Huperzine A (HupA) could protect neural stem cells against amyloid beta-peptide Aβ induced apoptosis in a neural stem cells (NSCs) and microglia co-culture system. Methods: Rat NSCs and microglial cells were isolated, cultured and identified with immunofluorescence Assays (IFA). Co-culture systems of NSCs and microglial cells were employed using Transwell Permeable Supports. The effects of Aβ_1-42 on NSCs were studied in 4 groups using co-culture systems: NSCs, Aβ+NSCs, co-culture and Aβ+co-culture groups. Bromodeoxyuridine (BrdU) incorporation and flow cytometry were utilized to assess the differences of proliferation, differentiation and apoptosis of NSCs between the groups. LQ test was performed to assess the amounts of IL-6, TNF-α and MIP-α secreted, and flow cytometry and Western blotting were used to assess apoptosis of NSCs and the expressions of Bcl-2 and Bax in each group. Results: IFA results showed that isolated rat NSCs were nestin-positive and microglial cells were CD11b/c-positive. Among all the groups, the Aβ+co-culture group has the lowest BrdU expression level, the lowest MAP2-positive, ChAT-positive cell counts and the highest NSC apoptosis rate. Smaller amounts of IL-6, TNF-α and MIP-α were being secreted by microglial cells in the HupA+Aβ+co-culture group compared with those in the Aβ+ co-culture group. Also the Bcl-2: Bax ratio was much higher in the HupA+Aβ+co-culture group than in the Aβ+co-culture group. Conclusions: HupA inhibits cell apoptosis through restraining microglia’s inflammatory response induced by Aβ_1-42.     

Ciliary neurotrophic factor (CNTF) plus soluble CNTF receptor α increases cyclooxygenase-2 expression, PGE2 release and interferon-γ-induced CD40 in murine microglia

Background

Beta amyloid (Aβ) peptides are the major constituents of the senile plaques present in Alzheimer's diseased brain. Pathogenesis has been associated with the aggregated form of the peptide as these fibrils are the conformation readily found in the plaques. However, recent studies have shown that the nonaggregated, soluble assemblies of Aβ have the potential to stimulate neuronal dysfunction and may play a prominent role in the pathogenesis of Alzheimer's disease.

Methods

Soluble, synthetic Aβ1–42 oligomers were prepared producing mainly dimer-trimer conformations as assessed by SDS-PAGE. Similar analysis demonstrated fibril preparations to produce large insoluble aggregates unable to migrate out of the stacking portion of the gels. These peptide preparations were used to stimulate primary murine microglia and cortical neuron cultures. Microglia were analyzed for changes in signaling response and secretory phenotype via Western analysis and ELISA. Viability was examined by quantifying lactate dehydrogenase release from the cultures.

Results

Aβ oligomers and fibrils were used to stimulate microglia for comparison. Both the oligomers and fibrils stimulated proinflammatory activation of primary microglia but the specific conformation of the peptide determined the activation profile. Oligomers stimulated increased levels of active, phosphorylated Lyn and Syk kinase as well as p38 MAP kinase compared to fibrils. Moreover, oligomers stimulated a differential secretory profile for interleukin 6, monocyte chemoattractant protein-1 and keratinocyte chemoattractant when compared to fibrils. Finally, soluble oligomers stimulated death of cultured cortical neurons that was exacerbated by the presence of microglia.

Conclusion

These data suggest that fibrils and oligomers stimulate unique signaling responses in microglia leading to discrete secretory changes and effects on neuron survival. This suggests that inflammation changes during disease may be the consequence of unique peptide-stimulated events and each conformation may represent an individual anti-inflammatory therapeutic target.     

MCAM,as a novel receptor for S100A8/A9, mediates progression of malignant melanoma through prominent activation of NF-κB and ROS formation upon ligand binding

The dynamic interaction between tumor cells and their microenvironment induces a proinflammatory milieu that drives cancer development and progression. The S100A8/A9 complex has been implicated in chronic inflammation, tumor development, and progression. The cancer microenvironment contributes to the up-regulation of this protein complex in many invasive tumors, which is associated with the formation of pre-metastatic niches and poor prognosis. Changing adhesive preference of cancer cells is at the core of the metastatic process that governs the reciprocal interactions of cancer cells with the extracellular matrices and neighboring stromal cells. Cell adhesion molecules (CAMs) have been confirmed to have high-level expression in various highly invasive tumors. The expression and function of CAMs are profoundly influenced by the extracellular milieu. S100A8/A9 mediates its effects by binding to cell surface receptors, such as heparan sulfate, TLR4 and RAGE on immune and tumor cells. RAGE has recently been identified as an adhesion molecule and has considerably high identity and similarity to ALCAM and MCAM, which are frequently over-expressed on metastatic malignant melanoma cells. In this study, we demonstrated that ALCAM and MCAM also function as S100A8/A9 receptors as does RAGE and induce malignant melanoma progression by NF-κB activation and ROS formation. Notably, MCAM not only activated NF-κB more prominently than ALCAM and RAGE did but also mediated intracellular signaling for the formation of lung metastasis. MCAM is known to be involved in malignant melanoma development and progression through several mechanisms. Therefore, MCAM is a potential effective target in malignant melanoma treatment.     

Suppression of inflammation response by a novel A₃ adenosine receptor agonist thio-Cl-IB-MECA through inhibition of Akt and NF-κB signaling

Adenosine, a purine nucleoside, is released from metabolically active cells into extracellular space and plays an important role in various pathophysiological processes. Adenosine regulates many biological responses including inflammation by the interaction with their receptors such as A₁, A_2A, A_2B, and A₃. Especially, A₃ adenosine receptor (A₃AR) is considered to be expressed in macrophage cells. To the end, A₃AR agonists have been reported to have an anti-inflammatory activity. In our continuous efforts to develop new anti-inflammatory agents, we found a novel adenosine analog, 2-chloro-N⁶-(3-iodobenzyl)-4′-thioadenosine-5′-N-methyluronamide (thio-Cl-IB-MECA), was a potent human A₃AR agonist. The study was designed to investigate whether thio-Cl-IB-MECA has an anti-inflammatory potential in mouse macrophage RAW 264.7 cells and mouse sepsis model in vivo. Thio-Cl-IB-MECA exhibited an effective anti-inflammatory activity. The expression of pro-inflammatory biomarkers including inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), and tumor necrosis factor (TNF-α) was suppressed by the treatment of thio-Cl-IB-MECA in the protein and mRNA levels in lipopolysaccharide (LPS)-stimulated mouse macrophage RAW 264.7 cells. Further examination revealed that thio-Cl-IB-MECA inhibited LPS-induced phosphatidylinositol 3-kinase (PI3 kinase)/Akt activation, NF-kB binding activity, and β-catenin expression. In addition, in in vivo LPS-induced mouse endotoxemia model, thio-Cl-IB-MECA exerted the increase of survival rate compared to vehicle-treated mouse. The analysis of the protein levels of iNOS, IL-1β, and TNF-α was also suppressed by the compound-treated groups in lung tissues. These results suggest that thio-Cl-IB-MECA might have an anti-inflammatory activity through the inhibition of pro-inflammatory cytokine expression by modulating PI3K/Akt and NF-κB signaling pathways.     

Ciliary neurotrophic factor (CNTF) plus soluble CNTF receptor α increases cyclooxygenase-2 expression, PGE2 release and interferon-γ-induced CD40 in murine microglia

Background  

Ciliary neurotrophic factor (CNTF) has been regarded as a potent trophic factor for motor neurons. However, recent studies have shown that CNTF exerts effects on glial cells as well as neurons. For instance, CNTF stimulates astrocytes to secrete FGF-2 and rat microglia to secrete glial cell line-derived neurotrophic factor (GDNF), which suggest that CNTF exerts effects on astrocytes and microglia to promote motor neuron survival indirectly. As CNTF is structurally related to IL-6, which can stimulate immune functions of microglia, we hypothesized that CNTF might exert similar effects.     

Is immunohistochemical epidermal growth factor receptor expression overestimated as a prognostic factor in head-neck squamous cell carcinoma? A retrospective analysis based on a tissue microarray of 365 carcinomas

Epidermal growth factor receptor is overexpressed in more than 80% of head-neck squamous cell carcinoma. Its role as an independent prognostic marker is discussed controversially. No standardized evaluation methods are reported. The aim of our study was to analyze the prognostic relevance of epidermal growth factor receptor expression, using a tissue microarray with more than 300 tumor samples. Epidermal growth factor receptor expression was analyzed by immunohistochemistry and fluorescence in situ hybridization based on a tissue microarray of 365 head-neck squamous cell carcinomas with complete clinicopathologic and follow-up data. Multiple independent observers blinded for clinical data evaluated epidermal growth factor receptor immunostaining semiquantitatively. Cut-off scores for positivity were determined systematically by receiver operating characteristic curve analysis and validated by resampling of the data. Epidermal growth factor receptor expression cut-off scores for loco-regional relapse and overall survival were determined to be 60%. No significant correlation with clinicopathologic data was found. Independent significant differences in loco-regional control and overall survival could not be distinguished by epidermal growth factor receptor expression. Epidermal growth factor receptor expression could not be confirmed as a significant independent prognostic marker in head-neck squamous cell carcinoma using a large tissue microarray with 365 head-neck squamous cell carcinomas with complete clinical data, an evaluation based on immunohistochemistry and fluorescence in situ hybridization by multiple independent observers and systematic determination of cut-off scores.     

Dopamine, by acting through its D2 receptor, inhibits insulin-like growth factor-I (IGF-I)-induced gastric cancer cell proliferation via up-regulation of Krüppel-like factor 4 through down-regulation of IGF-IR and AKT phosphorylation

The overexpression of insulin-like growth factor receptor-I (IGF-IR) and the activation of its signaling pathways both play critical roles in the development and progression of gastric cancer. Dopamine (DA), a major enteric neurotransmitter, has been reported to have a wide variety of physiological functions in the gastrointestinal tract, including the stomach. We have previously reported that both DA and tyrosine hydroxylase, the rate-limiting enzyme required for the synthesis of DA, are lost in malignant gastric tissues. The effect of this loss of DA on IGF-IR-induced growth of gastric cancer has not yet been elucidated; we therefore investigated the role of DA, if any, on IGF-IR-induced proliferation of malignant gastric cells. There was a significant increase in the expression of phosphorylated IGF-IR and its downstream signaling molecule AKT in human malignant gastric tissues compared with normal nonmalignant tissues. Furthermore, to determine whether this loss of DA has any effect on the activation of IGF-IR signaling pathways in malignant gastric tumors, in vitro experiments were undertaken, using AGS gastric cancer cells. Our results demonstrated that DA acting through its D(2) receptor, inhibits IGF-I-induced proliferation of AGS cells by up-regulating KLF4, a negative regulator of the cell cycle through down regulation of IGF-IR and AKT phosphorylation. Our results suggest that DA is an important regulator of IGF-IR function in malignant gastric cancer cells.     

Induction of apoptosis by A3 adenosine receptor agonist N6-(3-iodobenzyl)-adenosine-5′-N-methylcarboxamide in human leukaemia cells: a possible involvement of intracellular mechanism

Aim: The sensitivity of cancer cells which exhibit multi-drug resistance phenotype to A3 adenosine receptor (A3AR) agonist N⁶-(3-iodobenzyl)-adenosine-5′-N-methylcarboxamide (IB-MECA) was studied. Methods: To establish direct relationship between P-glycoprotein (P-gp, ABCB1 and MDR1) expression and IB-MECA induced cell death, a straightforward method for precise estimation of intracellular level of this A3AR agonist was developed. Results: We subjected three human leukaemia cell lines HL-60, K562 and K562/HHT to treatment with micromolar concentrations of IB-MECA. Although all cell lines used expressed A3AR, there was a large difference in their sensitivity to IB-MECA. While HL-60 and K562 cells were almost equally sensitive, the K562/HHT cells, which exhibit a multi-drug resistance phenotype because of overexpression of P-gp, were significantly more resistant. We found that the intracellular level of IB-MECA in K562/HHT cells was approx. 10 times lower than those in HL-60 or K562 cells. Inhibitors of P-gp, including cyclosporine A (CsA) and verapamil (Vpa), increased the intracellular level of IB-MECA and reversed the resistance of K562/HHT cells to this drug. Accordingly, shRNA-mediated down-regulation of P-gp significantly increased the intracellular level of IB-MECA in K562/HHT cells which simultaneously exhibited reduced resistance to this A3AR agonist. In addition, an in vitro enzyme-based assay provided evidence that IB-MECA might serve as a substrate for P-gp. Conclusion: Our results suggest that P-gp overexpression prevents cells from IB-MECA induced apoptosis despite the A3AR expression. Pro-apoptotic effect of IB-MECA seemed to strongly depend on its intracellular accumulation rather than on its interaction with A3AR.     

A cyclic pathway of P2 × 7, bradykinin,and dopamine receptor activation induces a sustained articular hyperalgesia in the knee joint of rats

Objective

We investigated whether: (1) P2?×?7 receptor activation by its agonist (BzATP) induces articular hyperalgesia in the rat’s knee joint via inflammatory mechanisms and (2) activation of P2?×?7 receptors by endogenous ATP contributes to the articular hyperalgesia induced by bradykinin, TNF-α, IL-1β, CINC-1, PGE_2, and dopamine.

Methods

The articular hyperalgesia was quantified using the rat knee joint incapacitation test. The knee joint inflammation, characterized by the concentration of pro-inflammatory cytokines and by neutrophil migration, was quantified in the synovial lavage fluid by ELISA and myeloperoxidase enzyme activity assay, respectively.

Results

BzATP induced a dose-dependent articular hyperalgesia in the rat’s knee joint that was significantly reduced by the selective antagonists for P2?×?7, bradykinin B₁ or B₂ receptors, β₁ or β₂ adrenoceptors, and by pre-treatment with Indomethacin. BzATP induced a local increase of TNF-α, IL-1β, IL-6, and CINC-1 concentration and neutrophil migration into the knee joint. The co-administration of the selective P2?×?7 receptor antagonist A-740003 significantly reduced the articular hyperalgesia induced by bradykinin and dopamine, but not by TNF-α, IL-1β, CINC-1, and PGE₂.

Conclusions

P2?×?7 receptor activation induces articular hyperalgesia mediated by the previous inflammatory mediator release. P2?×?7 receptor-induced articular hyperalgesia is sustained by the involvement of this purinergic receptor in bradykinin and dopamine-induced hyperalgesia in the knee joint.

     

Cordycepin as a sensitizer to tumour necrosis factor (TNF)-α-induced apoptosis through eukaryotic translation initiation factor 2α (eIF2α)- and mammalian target of rapamycin complex 1 (mTORC1)-mediated inhibition of nuclear factor (NF)-κB

Cordycepin (3′‐deoxyadenosine) is one of the major bioactive substances produced by Cordyceps militaris, a traditional medicinal mushroom. Cordycepin possesses several biological activities, including both pro‐apoptotic and anti‐apoptotic properties. In the present report, we investigated an effect of cordycepin on the survival of cells exposed to tumour necrosis factor (TNF)‐α. We found that subtoxic doses of cordycepin increased susceptibility of cells to TNF‐α‐induced apoptosis. It was associated with suppression of nuclear factor‐κB (NF‐κB), a major prosurvival component involved in TNF‐α signalling. The adenosine transporter and A₃ adenosine receptor, but not A₁ and A₂ adenosine receptors, mediated both anti‐NF‐κB and pro‐apoptotic effects. We found that cordycepin had the potential to phosphorylate eukaryotic translation initiation factor 2α (eIF2α) and that activation of eIF2α mimicked the suppressive effect of cordycepin on the NF‐κB pathway. Furthermore, activation of eIF2α sensitized cells to TNF‐α‐induced apoptosis. To identify molecular events downstream of eIF2α, the role of mammalian target of rapamycin complex 1 (mTORC1) was examined. Selective activation of ₃eIF2α, as well as treatment with cordycepin, caused phosphorylation of mTORC1. Rapamycin, an inhibitor of mTORC1, significantly reversed the suppressive effects of eIF2α on NF‐κB. These results suggest that cordycepin sensitizes cells to TNF‐α‐induced apoptosis, at least in part, via induction of the eIF2α–mTORC1 pathway and consequent suppression of NF‐κB.     

Exendin-4, a glucagon-like peptide-1 receptor agonist,inhibits Aβ25-35-induced apoptosis in PC12 cells by suppressing the expression of endoplasmic reticulum stress-related proteins

Neurodegenerative disorders are chronic and progressive disease. Exendin-4 (Ex-4) can function as a neuroprotective agent and has novel therapeutic ability for the treatment of neurodegenerative disorders. In this study, we aimed to explore the neuroprotective effect of Ex-4 on PC12 cell apoptosis induced by Aβ_25-35 in molecular level. The apoptosis of PC12 cells was detected by MTT assay, TUNEL staining and flow cytometry. The expression of ERS (endoplasmic reticulum stress, ERS) related proteins such as CHOP, GRP78 and Caspase-12 were determined by Western blot and cell immunocytochemistry. Results showed the apoptotic rate of PC12 cells significantly increased after Aβ_25-35 addition, which was remarkably reduced after Ex-4 treatment. The expression of CHOP, GRP78 and Caspase-12 were significantly upregulated, and then remarkably reduced after Ex-4 treatment, while in the presence of Exendin9-39, the effect of Ex-4 was reversed. In conclusion, endoplasmic reticulum stress might be involved in the apoptosis process of PC12 cell induced by Aβ_25-35 and Ex-4 might provide a potential strategy for the treatment and prevention of cell apoptosis-associated disorders.     

Contrasting actions of a convulsant barbiturate and its anticonvulsant enantiomer on the α1β3γ2L GABAA receptor account for their in vivo effects

Key Points

• Most barbiturates are anaesthetics but unexpectedly a few are convulsants whose mechanism of action is poorly understood.
• We synthesized and characterized a novel pair of chiral barbiturates that are capable of photolabelling their binding sites on GABA_A receptors. In mice the S‐enantiomer is a convulsant, but the R‐enantiomer is an anticonvulsant.
• The convulsant S‐enantiomer binds solely at an inhibitory site. It is both an open state inhibitor and a resting state inhibitor. Its action is pH independent, suggesting the pyrimidine ring plays little part in binding. The inhibitory site is not enantioselective because the R‐enantiomer inhibits with equal affinity.
• In contrast, only the anticonvulsant R‐enantiomer binds to the enhancing site on open channels, causing them to stay open longer. The enhancing site is enantioselective.
• The in vivo actions of the convulsant S‐enantiomer are accounted for by its interactions with GABA_A receptors.

Abstract

Most barbiturates are anaesthetics but a few unexpectedly are convulsants. We recently located the anaesthetic sites on GABA_A receptors (GABA_ARs) by photolabelling with an anaesthetic barbiturate. To apply the same strategy to locate the convulsant sites requires the creation and mechanistic characterization of a suitable agent. We synthesized enantiomers of a novel, photoactivable barbiturate, 1‐methyl‐5‐propyly‐5‐(m‐trifluoromethyldiazirinyl) phenyl barbituric acid (mTFD‐MPPB). In mice, S‐mTFD‐MPPB acted as a convulsant, whereas R‐mTFD‐MPPB acted as an anticonvulsant. Using patch clamp electrophysiology and fast solution exchange on recombinant human α₁β₃γ_2L GABA_ARs expressed in HEK cells, we found that S‐mTFD‐MPPB inhibited GABA‐induced currents, whereas R‐mTFD‐MPPB enhanced them. S‐mTFD‐MPPB caused inhibition by binding to either of two inhibitory sites on open channels with bimolecular kinetics. It also inhibited closed, resting state receptors at similar concentrations, decreasing the channel opening rate and shifting the GABA concentration–response curve to the right. R‐mTFD‐MPPB, like most anaesthetics, enhanced receptor gating by rapidly binding to allosteric sites on open channels, initiating a rate‐limiting conformation change to stabilized open channel states. These states had slower closing rates, thus shifting the GABA concentration–response curve to the left. Under conditions when most GABA_ARs were open, an inhibitory action of R‐mTFD‐MPPB was revealed that had a similar IC₅₀ to that of S‐mTFD‐MPPB. Thus, the inhibitory sites are not enantioselective, and the convulsant action of S‐mTFD‐MPPB results from its negligible affinity for the enhancing, anaesthetic sites. Interactions with these two classes of barbiturate binding sites on GABA_ARs underlie the enantiomers’ different pharmacological activities in mice.

Abbreviations

C

channel closed, resting state

CD₅₀

median clonic siezure dose

CI

confidence interval

G₂O

open channel state bound with two GABA molecules

GABA_AR

GABA receptor Type A

HEK

human embryonic kidney

I

peak current amplitude

I_max

maximal peak current amplitude

k₋₁

dissociation rate constant

k₊₁

binding rate constant

k_act

activation energy

LoRR

loss of righting reflex

MPPB

1‐methyl‐5‐phenyl‐5‐propyl‐barbituric acid

nAChR

nicotinic acetylcholine receptor

O

open channel state

O’

stabilized open channel state

pK

acid dissociation constant

PTZ

pentylenetetrazol

R‐mTFD‐MPAB

R‐5‐allyl‐1‐methyl‐5‐(m‐trifluoromethyl‐diazirynylphenyl) barbituric acid

R‐mTFD‐MPPB

R‐1‐methyl‐5‐propyly‐5‐(m‐trifluoromethyldiazirinyl) phenyl barbituric acid

S‐mTFD‐MPAB

S‐5‐allyl‐1‐methyl‐5‐(m‐trifluoromethyl‐diazirynylphenyl) barbituric acid

S‐mTFD‐MPPB

S‐1‐methyl‐5‐propyly‐5‐(m‐trifluoromethyldiazirinyl) phenyl barbituric acid

TID

3‐(trifluoromethyl)‐3‐(m‐iodophenyl) diazirine

α

channel closing rate

β

channel opening rate

     

Inflammatory mediators mediate airway smooth muscle contraction through a G protein-coupled receptor–transmembrane protein 16A–voltage-dependent Ca2+ channel axis and contribute to bronchial hyperresponsiveness in asthma

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