Ginsenosides Rg1 and Rb1 enhance glutamate release through activation of protein kinase A in rat cerebrocortical nerve terminals (synaptosomes)

We examined the effect of ginsenoside Rg1 or Rb1, the active ingredients of ginseng, on the release of endogenous glutamate from glutamatergic nerve terminals purified from rat cerebral cortex. Result showed that the Ca(2+)-dependent release of glutamate evoked by 4-aminopyridine was facilitated by ginsenoside Rg1 or Rb1 in a concentration-dependent manner. Sequential experiments reveal that ginsenoside Rg1 or Rb1-mediated facilitation of glutamate release (i) results from an enhancement of vesicular exocytosis; (ii) is not due to an alternation of synaptosomal excitability; (iii) is associated with an increase in Ca(2+) influx through presynaptic N- and P/Q-type voltage-dependent Ca(2+) channels; (iv) appears to involve a protein kinase A pathway. These results conclude that ginsenoside Rg1 or Rb1 exerts their presynaptic facilitatory effect, likely through the activation of protein kinase A, which subsequently enhances Ca(2+) entry to cause an increase in evoked glutamate release from rat cortical synaptosomes. This finding might provide important information regarding the action of ginseng in the central nervous system.     

Catechin-induced activation of the LKB1/AMP-activated protein kinase pathway

Catechins are abundant in green tea and induce a variety of biologic actions, including anti-cancer, anti-obesity, and anti-diabetes effects, and their clinical application has been widely investigated. To clarify the underlying molecular mechanisms of these actions, we examined the effect of catechins on AMP-activated protein kinase (AMPK) in cultured cells and in mice. In Hepa 1-6, L6, and 3T3-L1 cells, epigallocatechin gallate (EGCG) induced increases in AMPKα and the downstream target acetyl-CoA carboxylase (ACC) phosphorylation, and AMPKα activity. Analysis of the molecular specificity of eight naturally occurring catechins revealed that catechins with a gallocatechin moiety or a galloyl residue act as AMPK activators. In addition, phosphorylation of LKB1, which is a tumor-suppressor protein and a major AMPK-kinase, was increased by catechin treatment. EGCG-induced phosphorylation of LKB1 and AMPKα was suppressed by treatment with catalase, suggesting that reactive oxygen species are involved in EGCG-induced activation of the LKB1/AMPK pathway. Oral administration of EGCG (200 mg/kg body weight) to BALB/c mice induced an increase in AMPKα activity in the liver concomitant with a significant increase in AMPKα and ACC phosphorylation. EGCG administration also increased oxygen consumption and fat oxidation, as determined by indirect calorimetry. These findings suggest that multiple effects of catechins, including anti-obesity and anti-cancer effects, are mediated, at least in part, by the activation of LKB1/AMPK in various tissues, and that these effects vary according to the catechin structure.     

Cannabinoid CB(2) receptors modulate ERK-1/2 kinase signalling and NO release in microglial cells stimulated with bacterial lipopolysaccharide

BACKGROUND AND PURPOSE

Cannabinoid (CB) receptor agonists have potential utility as anti-inflammatory drugs in chronic immune inflammatory diseases. In the present study, we characterized the signal transduction pathways affected by CB₂ receptors in quiescent and lipopolysaccharide (LPS)-stimulated murine microglia.

EXPERIMENTAL APPROACH

We examined the effects of the synthetic CB₂ receptor ligand, JWH-015, on phosphorylation of MAPKs and NO production.

KEY RESULTS

Stimulation of CB₂ receptors by JWH-015 activated JNK-1/2 and ERK-1/2 in quiescent murine microglial cells. Furthermore, CB₂ receptor activation increased p-ERK-1/2 at 15 min in LPS-stimulated microglia. Surprisingly, this was reduced after 30 min in the presence of both LPS and JWH-015. The NOS inhibitor l-NAME blocked the ability of JWH-015 to down-regulate the LPS-induced p-ERK increase, indicating that activation of CB₂ receptors reduced effects of LPS on ERK-1/2 phosphorylation through NO. JWH-015 increased LPS-induced NO release at 30 min, while at 4 h CB₂ receptor stimulation had an inhibitory effect. All the effects of JWH-015 were significantly blocked by the CB₂ receptor antagonist AM 630 and, as the inhibition of CB₂ receptor expression by siRNA abolished the effects of JWH-015, were shown to be mediated specifically by activation of CB₂ receptors.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate that CB₂ receptor stimulation activated the MAPK pathway, but the presence of a second stimulus blocked MAPK signal transduction, inhibiting pro-inflammatory LPS-induced production of NO. Therefore, CB₂ receptor agonists may promote anti-inflammatory therapeutic responses in activated microglia.     

Withaferin A down-regulates lipopolysaccharide-induced cyclooxygenase-2 expression and PGE2 production through the inhibition of STAT1/3 activation in microglial cells

Microglia are the major immune effector cells in the brain, and microglia activated by injury and infection can produce inflammatory mediators. A number of studies have reported that withaferin A has anti-inflammatory functions. However, the effects of withaferin A on the microglial inflammatory response have not been investigated. Our results show that withaferin A inhibited lipopolysaccharide (LPS)-induced cyclooxygenase (COX)-2 mRNA and protein expression and prostaglandin E2 (PGE(2)) production in BV2 murine microglial cells. Withaferin A had no effect on LPS-induced Akt and ERK phosphorylation, but phosphorylation of p38 and JNK was slightly decreased by withaferin A. Withaferin A significantly inhibited LPS-induced STAT1 and STAT3 phosphorylation in a dose-dependent manner. Furthermore, withaferin A inhibited nuclear translocation of STAT1 and interferon-gamma activated sequence (GAS)-promoter activity. Taken together, these results suggest that withaferin A inhibits LPS-induced PGE(2) production and COX-2 expression, at least in part, by blocking STAT1 and STAT3 activation.     

Prevention of inflammation-mediated neurotoxicity by Rg3 and its role in microglial activation

Considering the importance of inflammation and apoptosis in neurodegenerative conditions, the potential suppressive effects of the Rg3, a by-product obtained during the steaming of red ginseng, may indicate that Rg3 could provide a beneficial therapeutic approach to treating or preventing neurodegenerative disease. We investigated the effect of Rg3 on Abeta42-mediated microglial activation and inflammation-mediated neurotoxicity in murine BV-2 microglial and Neuro-2a neuroblastoma cells, respectively. Rg3 effectively reduced inflammatory cytokine expression in Abeta42-treated BV-2, and inhibited the binding of NF-kappaB p65 to its DNA consensus sequences, and significantly reduced the expression of TNF-alpha in activated microglia. Pretreatment with Rg3 increased the survival rate of Neuro-2a exposed to TNF-alpha. These observations suggest that Rg3 reduced neurotoxicity by inhibiting chronic inflammation through the suppression of activated microglia. In addition, the expression of pro-inflammatory cytokines in BV-2 stimulated by Abeta42 was decreased but not eliminated by Rg3 when binding to the macrophage scavenger receptor type A (MSRA) was blocked with fucoidan. This implies that the inflammatory response may not be exclusively triggered via MSRA. More interestingly, iNOS was almost completely inhibited in the presence of Rg3 when MSRA binding was blocked with fucoidan. Moreover, Rg3 increased the expression of MSRA in BV-2 transfected with siRNA targeting MSRA mRNA, and this increased MSRA expression may play a role in the phagocytosis of Abeta42 peptides. Our results indicate that inhibition of the inflammatory repertoire of microglia, neuroprotection, and increased MSRA expression induced by Rg3 may at least partly explain its therapeutic effects in chronic neurodegenerative diseases.     

Dexamethasone up-regulates the inhibitory adaptor protein Dok-1 and suppresses downstream activation of the mitogen-activated protein kinase pathway in antigen-stimulated RBL-2H3 mast cells

The glucocorticoid dexamethasone suppresses antigen-induced degranulation, cytokine production, and intermediate signaling events in RBL-2H3 mast cells, although the exact mechanisms are uncertain. By microarray analysis, we discovered that expression of the inhibitory adaptor protein, downstream of tyrosine kinase (Dok)-1, was up-regulated 4-fold in dexamethasone-treated RBL-2H3 cells. The up-regulation was apparent with as little as 1 to 10 nM dexamethasone. Treatment with dexamethasone also enhanced tyrosine phosphorylation of Dok-1, augmented recruitment of Ras GTPase-activating protein (RasGAP) by Dok-1, and inhibited activation of the mitogen-activated protein (MAP) kinase pathway in antigen-stimulated cells. The same effects were obtained by transient overexpression of Dok-1 but not by overexpression of Dok-1 that was mutated in RasGAP-binding domain. The negative regulatory role of Dok-1 was further validated by the expression of small interfering RNA directed against Dok-1, which enhanced activation of MAP kinase and subsequent release of arachidonic acid and tumor necrosis factor-alpha. These findings identify Dok-1 as mediator of the antiallergic actions of dexamethasone and as a negative regulator of the MAP kinase pathway and downstream release of inflammatory mediators.     

ERK/MAPK信号转导途径在急性髓系白血病发病机制中的作用

目的:研究急性髓系白血病细胞外信号调节激酶(ERK)/丝裂原活化蛋白激酶(M APK)的表达水平及其意义。方法:以急性髓系白血病细胞株HL-60细胞,31例初治急性髓系白血病(AM L)、14例AM L完全缓解(CR)和15例正常供髓者骨髓细胞为研究对象,应用流式细胞术检测磷酸化ERK 1/2信号分子的表达。结果:HL-60细胞,初治AM L、AM L-CR及正常骨髓细胞均表达磷酸化ERK 1/2,但表达水平不同。HL-60、初治AM L细胞与AM L-CR、正常细胞相比,磷酸化ERK 1/2表达水平均显著增高(P<0.05),高表达磷酸化ERK 1/2的初治AM L比例为80.6%(25/31)。结论:ERK/M APK信号途径的构成性激活在急性髓系白血病的发病中起重要作用。     

甘油水溶液对人参皂苷Rg1在大鼠体内生物利用度的影响

目的 以三七总皂苷为样品,考察不同浓度的甘油水溶液对人参皂苷Rg1在大鼠体内的药动学参数和生物利用度的影响.方法 静脉注射(i.v.)和十二指肠给药(i.d.)后,采集血样,HPLC-UV法测定大鼠血浆中人参皂苷Rg1的浓度,绘制药-时曲线并计算药动学参数及生物利用度.结果 大鼠十二指肠注射给予PNS-甘油水溶液(Rg1剂量175.68mg·kg-1,甘油浓度分别为:20%、40%、60%、80%)、PNS-水溶液(Rg1剂量439.2mg·kg-1)后,人参皂苷Rg1的达峰时间Tmax分别为(0.25±0.00)h、(0.438±0.125)h、(0.375±0.144)h、(0.313±0.125)h、(0.5±0.00)h,AUC(0~t)分别为(9.099±1.452) 、(18.727±2.058) 、(4.625±1.102) 、(2.756±1.022)、(6.012±0.647)μg/(min·mL),其绝对生物利用度分别为4.13%、8.51%、2.10%、1.25%、1.09%.结论 各浓度甘油溶液均能较大提高三七总皂苷中人参皂苷Rg1的绝对生物利用度,其中浓度为40%的效果最佳.     

人参皂苷Rg3与Rh2的研究进展

人参是我国传统的名贵中草药材,人参皂苷是人参的主要有效成分。人参皂苷Rg3,Rh2具有抗疲劳、舒张血管、提高免疫力、抗肿瘤等药理作用。综述了人参皂苷Rg3,Rh2的药理作用及制备方法。     

人参皂苷Rg1对培养大鼠骨髓间充质干细胞增殖影响的机制研究

目的研究人参皂苷Rg1对大鼠骨髓间充质干细胞(BMSC)增殖影响的可能机制。方法分离培养大鼠骨髓间充质干细胞,分为药物干预组、对照组,药物干预组以1×10-6mol.L-1人参皂苷Rg1孵育48h,对照组未加药物常规培养;分别用骨髓CFU-F体外培养法、胸腺嘧啶核苷参入法及MTT法测定大鼠BMSC的增殖情况,同时测定BMSC的GATA转录因子1～3的表达及其与DNA结合活性。结果人参皂苷Rg1刺激后BMSC的GATA1和GATA2 mRNA表达与对照组相比分别上调1.42±0.31(P<0.01)和2.70±0.73(P<0.01)倍,并且人参皂苷Rg1刺激后BMSC的GATA与DNA结合活性明显增高。结论人参皂苷Rg1可促进大鼠BMSC增殖,其机制可能是通过上调GATA1和GATA2的表达以及其与DNA的结合活性来实现。     

Differential involvement of p38 mitogen-activated protein kinase and phosphatidyl inositol 3-kinase in the IL-1-mediated NF-kappa B and AP-1 activation

Interleukin-1 (IL-1) is a central regulator of the immune and inflammatory responses by which various inflammatory genes are induced. Although IL-1 signaling is known to involve PI3-kinase, p38 mitogen-activated protein (MAP) kinase and extracellular signal-regulated kinase (ERK), the crosstalk of these kinases on the IL-1-mediated signal transduction is not clear. We used two specific inhibitors, SB203580 which selectively inhibits p38 MAP kinase and LY294002 which inhibits PI3-kinase, respectively, to explore the involvement of these kinases in the IL-1-induced NF-kappa B activation, using a human glioblastoma cell line, T98G. Two kinase inhibitors decreased IL-1-induced IL-8 mRNA and protein levels markedly. IL-1 caused phosphorylation of p38 MAP kinase with concomitant recruitment of PI3-kinase to IL-1 receptor I (IL-1RI) and its activation. In this context, pretreatment of LY294002, but not SB203580, inhibited IL-1-induced NF-kappa B activation significantly. While IL-1 induced-AP-1 activation was moderate, both LY294002 and SB203580 suppressed IL-1-induced AP-1 activation. These observations were prominent particularly in the TRAF6 transfection system, in which overexpression of wild type TRAF6 augmented the IL-1 mediated NF-kappa B and AP-1 activation, while dominant negative TRAF6 construct (delta TRAF6) suppressed these activation. Namely, LY294002 inhibited TRAF6-mediated IL-1-induced NF-kappa B and AP-1 activation markedly, while SB203580 inhibited TRAF6-induced AP-1 activation but not NF-kappa B activation. Above results indicated that both PI3-kinase and p38 MAP kinase are differentially involved in IL-1-induced NF-kappa B and AP-1 activation.     

Protein kinase C epsilon-dependent pathway of extracellular signal-regulated protein kinase activation by P2Y1 and P2Y2 purinoceptors that activate cytosolic phospholipase A2 in endothelial cells.

The aim of this study was to investigate the stimulating effects on arachidonic acid release of P2Y1 and P2Y2 receptor-selective agonists, 2-methylthio-ATP (2MeSATP) and UTP, respectively, in bovine pulmonary artery endothelial cells. Exposure of cells to 2MeSATP and UTP led to the release of arachidonic acid, a response which was abolished by the removal of extracellular Ca2+ and methyl arachidonyl fluorophosphonate. Phorbol 12-myristate 13-acetate (PMA) itself not only stimulated arachidonic acid release but also played a permissive role in the response to UTP. However, PMA failed to enhance the arachidonic acid response induced by 2MeSATP, probably due to greater attenuation of the [Ca2+]i increase caused by 2MeSATP than UTP. Inhibition of protein kinase C with Ro 31-8220 (1-[3-(amidinothio) propyl-1H-indoyl-3-yl]-3-(1-methyl-1H-indoyl-3-yl)-maleimide -methane sulphate) and staurosporine, but not with Go 6976 (12-(-2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-indolo(2, 3-a)pyrrolo(3,4-c)carbazole), reduced the arachidonic acid response of 2MeSATP, UTP and PMA. PMA-induced potentiation of the UTP response reached a maximum after a 1-h preincubation, then declined and eventually lost its effect when the preincubation lasted up to 8 h. Among the protein kinase C isoforms present in endothelial cells, betaI and epsilon could be down-regulated by treatment with PMA for 4-24 h. PD 098059 (2-(2-Amino-3-methoxyphenyl)-4H-1-benzopyran-4-one) inhibited extracellular signal-regulated protein kinase activation, cytosolic phospholipase A2 phosphorylation and arachidonic acid release caused by 2MeSATP, UTP and PMA. Taken together, our results demonstrate that P2Y1 and P2Y2 purinoceptors mediate arachidonic acid release by activating cytosolic phospholipase A2 through an elevation of [Ca2+]i and protein kinase C epsilon-, extracellular signal-regulated protein kinase-dependent phosphorylation.     

Caffeine suppresses TNF-alpha production via activation of the cyclic AMP/protein kinase A pathway

This study investigated the effect of in vitro exposure to caffeine, and its major metabolite paraxanthine, at concentrations relevant to typical caffeine consumption in humans, on lipopolysaccharide (LPS)-stimulated cytokine production in human whole blood. In addition, a role for the cyclic AMP/protein kinase A (PKA) pathway in the immunomodulatory effect of caffeine was investigated. Diluted whole blood (taken following >/=15 h abstinence from caffeine-containing food and beverages) was preincubated with caffeine or paraxanthine (10-100 microM) and stimulated with LPS (1 proportional, variant g/ml) for 24 h. The proinflammatory cytokines tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-12, and the antiinflammatory cytokine IL-10 were measured in cell-free supernatants. Whilst caffeine and paraxanthine had little or no effect on IL-10, IL-1beta, or IL-12 production, TNF-alpha production was suppressed in all individuals studied. The effect was statistically significant at 100 microM and consistent across seven experiments performed. Although not statistically significant, a similar effect was observed with paraxanthine. Caffeine (100 microM) also increased intracellular cyclic AMP concentrations in LPS-stimulated monocytes isolated from whole blood. Moreover, the effect of caffeine on TNF-alpha production was abolished by pretreatment with the protein kinase A inhibitor Rp-8-Br-cAMPS (10(-4) and 10(-5)M). To conclude, this study demonstrates that concentrations of caffeine that are relevant to human consumption consistently suppress production of the proinflammatory cytokine TNF-alpha in human blood and that this effect is mediated by the cyclic AMP/protein kinase A pathway.     

Examination of signal transduction pathway of stimulated B1 and B2 kinin receptors; MAP kinase pathway to AP-1 translocation in HEK 293 cells

B1 or B2 kinin receptor-overexpressing HEK293 cells were stimulated with des-Arg9-BK or BK, respectively. Each agonist induced translocation of AP-1 into the nuclear fraction as well as activation of MAP kinases in each cells. MAP kinase inhibitor PD98059 suppressed translocation of AP-1 and agonist-induced MAP kinase activation in both cells. These results indicate that stimulation of B1 or B2 receptor expresses a feature of the signal transduction pathway of MAP kinase activation to translocation of AP-1. This signal transduction pathway of HEK cells through B1 and B2 receptors may be similar in response to respective agonists.     

Porphyromonas gingivalis, Periodontal pathogen, lipopolysaccharide induces angiogenesisvia extracellular signal-regulated kinase 1/2 activation in human vascular endothelial cells

Porphyromonas gingivalis is a major periodontal pathogen. The lipopolysaccharide (LPS) secreted from P. gingivalis is implicated in the initiation and progression of periodontitis. Aberrant angiogenesis is often associated with lesion formation in chronic periodontitis. In this study, we report that P. gingivalis LPS activates angiogenic cascade, migration, invasion and tube formation in human umbilical vein endothelial cells (HUVECs). Furthermore, P. gingivalis LPS potently stimulated in vivo neovascularization in chick chorioallantoic membrane (CAM) and the mouse Matrigel plug assay. P. gingivalis LPS had no effect on the expression of vascular endothelial growth factor (VEGF) or its receptor, Flk-1, implying that P. gingivalis LPS-induced angiogenesis may result from its direct action on endothelial cells. P. gingivalis LPS evoked activation of the mitogen-activated protein kinase ERK1/2 in HUVECs, which is closely linked to angiogenesis. Taken together, these results strongly suggest P. gingivalis LPS plays an important role in the pathological angiogenesis for periodontal diseases, such as periodontitis.     

Petasites hybridus extracts in vitro inhibit COX-2 and PGE2 release by direct interaction with the enzyme and by preventing p42/44 MAP kinase activation in rat primary microglial cells

Rhizomes of butterbur, Petasites hybridus L. (Asteraceae), have been used since ancient times for the treatment of inflammatory diseases. In the present study, the effects of lipophilic extracts from rhizomes of Petasites hybridus on the formation and release of prostaglandin E2 were investigated. The extracts had different contents of petasin and isopetasin: A: 2.1 % and 0.4 %, B: 0.2 % and 0.1 %, C: 12.1 % and 6.1 % and D: 21.9 % and 9.4 %, respectively. Direct inhibition of cyclooxygenase (COX) -1 and -2 isoenzymes and inhibition of the expression of COX-2 and p42/44 MAP kinase in rat primary microglial cells were tested. All extracts were found to be only weak direct inhibitors of COX-1 (IC50> 400 microg/mL). However, most extracts revealed a strong inhibitory activity against the inducible isoform COX-2 ( A: IC50=30.4 microg/mL; B: IC50=60.6 microg/mL; C: IC50=22.6 microg/mL; D: IC50=20.0 microg/mL). This activity was not correlated to the content of petasin and isopetasin. Pure petasin and isopetasin neither inhibited COX-1 nor COX-2 (IC50 > 400 microM for both compounds and enzymes). Petasites extracts dose-dependently inhibited LPS-induced and thus COX-2-mediated PGE2 release in primary rat microglial cells (A: IC50= 2.4 microg/mL; C: IC50=5.8 microg/mL and D: IC50=4.6 microg/mL). Also this effect was independent from the petasin and isopetasin content. COX-2 synthesis in microglia was totally blocked with 5 microg/mL of C whereas COX-1 synthesis was not influenced. C and D did not affect the LPS-induced activation of p38 MAPK and IkappaBalpha, but they prevented the LPS-induced activation of p42/44 MAPK. Therefore, these Petasites hybridus extracts can be regarded as natural selective inhibitors of COX-2 and its expression, an effect which is independent from the petasin content.