Silica Nanoparticles Induce Hepatotoxicity by Triggering Oxidative Damage, Apoptosis, and Bax-Bcl2 Signaling Pathway.

The increase in the usage of silica nanoparticles (SiNPs) in the industrial and medical fields has raised concerns about their possible adverse effects on human health. The present study aimed to investigate the potential adverse effects of SiNPs at daily doses of 25 and 100 mg/kg body weight intraperitoneally (i.p.) for 28 consecutive days on markers of liver damage in adult male rats. Results revealed that SiNPs induced a marked increase in serum markers of liver damage, including lactate dehydrogenase (LDH), alanine aminotransferase (ALAT), and aspartate aminotransferase (ASAT). SiNPs also induced an elevation of reactive oxygen species (ROS) production in liver, along with an increase in oxidative stress markers (NO, MDA, PCO, and H2O2), and a decrease in antioxidant enzyme activities (CAT, SOD, and GPx). Quantitative real-time PCR showed that SiNPs also induced upregulation of pro-apoptotic gene expression (including Bax, p53, Caspase-9/3) and downregulation of anti-apoptotic factors Bcl-2. Moreover, histopathological analysis revealed that SiNPs induced hepatocyte alterations, which was accompanied by sinusoidal dilatation, Kupffer cell hyperplasia, and the presence of inflammatory cells in the liver. Taken together, these data showed that SiNPs trigger hepatic damage through ROS-activated caspase signaling pathway, which plays a fundamental role in SiNP-induced apoptosis in the liver.

Panoptic imaging of transparent mice reveals whole-body neuronal projections and skull-meninges connections.

Analysis of entire transparent rodent bodies after clearing could provide holistic biological information in health and disease, but reliable imaging and quantification of fluorescent protein signals deep inside the tissues has remained a challenge. Here, we developed vDISCO, a pressure-driven, nanobody-based whole-body immunolabeling technology to enhance the signal of fluorescent proteins by up to two orders of magnitude. This allowed us to image and quantify subcellular details through bones, skin and highly autofluorescent tissues of intact transparent mice. For the first time, we visualized whole-body neuronal projections in adult mice. We assessed CNS trauma effects in the whole body and found degeneration of peripheral nerve terminals in the torso. Furthermore, vDISCO revealed short vascular connections between skull marrow and brain meninges, which were filled with immune cells upon stroke. Thus, our new approach enables unbiased comprehensive studies of the interactions between the nervous system and the rest of the body.

Anti-neuroinflammatory effects of Ginkgo biloba extract EGb761 in LPS-activated primary microglial cells.

BACKGROUND: Neuroinflammation is a key factor of Alzheimer's disease (AD) and other neurodegenerative conditions. Microglia are the resident mononuclear immune cells of the central nervous system (CNS). They play an essential role in the maintenance of homeostasis and responses to neuroinflammation. Ginkgo biloba extract EGb 761 is one of the most commonly used natural medicines owing to its established efficacy and remarkable biological activities especially in respect to CNS diseases. However, only few studies have addressed the effects and mechanisms of Ginkgo biloba extract in microglia activation. METHODS: We measured the production of pro-inflammatory mediators and cytokines by ELISA and analyzed gene expressions by qRT-PCR and Western Blot in LPS treated cultured primary rat microglia. RESULTS: The Ginkgo biloba extract EGb 761 significantly inhibited the release of prostaglandin E2 (PGE2) and differentially regulated the levels of pro-inflammatory cytokines. The inhibition of LPS-induced PGE2 release in primary microglia was partially dependent on reduced protein synthesis of mPGES-1 and the reduction in the activation of cytosolic phospholipase A2 (cPLA2) without altering COX-2 enzymatic activity, inhibitor of kappa B alpha (IkappaBalpha) degradation, and the activation of multiple mitogen activated protein kinases (MAPKs). Altogether, we showed that EGb 761 reduces neuro-inflammatory activation in primary microglial cells by targeting PGE2 release and cytokines. CONCLUSION: Ginkgo biloba extract EGb 761 displayed anti-neuroinflammatory activity in LPS-activated primary microglia cells. EGb 761 was able to reduce neuroinflammatory activation by targeting the COX/PGE2 pathway. This effect might contribute to the established clinical cognitive efficacy in Alzheimer's disease, vascular and mixed dementia.

Inflammatory and oxidative mechanisms potentiate bifenthrin-induced neurological alterations and anxiety-like behavior in adult rats.

Bifenthrin (BF) is a synthetic pyrethroid pesticide widely used in several countries to manage insect pests on diverse agricultural crops. Growing evidence indicates that BF exposure is associated with an increased risk of developing neurodegenerative disorders. However, the mechanisms by which BF induces neurological and anxiety alterations in the frontal cortex and striatum are not well known. The present in vivo study was carried out to determine whether reactive oxygen species (ROS)-mediated oxidative stress (OS) and neuroinflammation are involved in such alterations. Thirty-six Wistar rats were thus randomly divided into three groups and were orally administered with BF (0.6 and 2.1 mg/kg body weight, respectively) or the vehicle (corn oil), on a daily basis for 60 days. Results revealed that BF exposure in rats enhanced anxiety-like behavior after 60 days of treatment, as assessed with the elevated plus-maze test by decreases in the percentage of time spent in open arms and frequency of entries into these arms. BF-treated rats also exhibited increased oxidation of lipids and carbonylated proteins in the frontal cortex and striatum, and decreased glutathione levels and antioxidant enzyme activities including superoxide dismutase, catalase and glutathione peroxidase. Treatment with BF also increased protein synthesis and mRNA expression of the inflammatory mediators cyclooxygenase-2 (COX-2), microsomal prostaglandin synthase-1 (mPGES-1) and nuclear factor-kappaBp65 (NF-kBp65), as well as the production of tumor necrosis factor-α (TNF-α) and ROS. Moreover, BF exposure significantly decreased protein synthesis and mRNA expression of nuclear factor erythroid-2 (Nrf2) and acetylcholinesterase (AChE), as well as gene expression of muscarinic-cholinergic receptors (mAchR) and choline acetyltransferase (ChAT) in the frontal cortex and striatum. These data suggest that BF induced neurological alterations in the frontal cortex and striatum of rats, and that this may be associated with neuroinflammation and oxidative stress via the activation of Nrf2/NF-kBp65 pathways, which might promote anxiety-like behavior.

Inhibition of neuroinflammation by thymoquinone requires activation of Nrf2/ARE signalling.

Thymoquinone is an antioxidant phytochemical that has been shown to inhibit neuroinflammation. However, little is known about the potential roles of intracellular antioxidant signalling pathways in its anti-inflammatory activity. The objective of this study was to elucidate the roles played by activation of the Nrf2/ARE antioxidant mechanisms in the anti-inflammatory activity of this compound. Thymoquinone inhibited lipopolysaccharide (LPS)-induced neuroinflammation through interference with NF-κB signalling in BV2 microglia. Thymoquinone also activated Nrf2/ARE signalling by increasing nuclear localisation, DNA binding and transcriptional activity of Nrf2, as well as increasing protein levels of HO-1 and NQO1. Suppression of Nrf2 activity through siRNA or with the use of trigonelline resulted in the loss of anti-inflammatory activity by thymoquinone. Taken together, our studies show that thymoquinone inhibits NF-κB-dependent neuroinflammation in BV2 microglia, by targeting antioxidant pathway involving activation of both Nrf2/ARE. We propose that activation of Nrf2/ARE signalling pathway by thymoquinone probably results in inhibition of NF-κB-mediated neuroinflammation.

Alleviation of Microglial Activation Induced by p38 MAPK/MK2/PGE2 Axis by Capsaicin: Potential Involvement of other than TRPV1 Mechanism/s.

Exaggerated inflammatory responses in microglia represent one of the major risk factors for various central nervous system's (CNS) associated pathologies. Release of excessive inflammatory mediators such as prostaglandins and cytokines are the hallmark of hyper-activated microglia. Here we have investigated the hitherto unknown effects of capsaicin (cap) - a transient receptor potential vanilloid 1 (TRPV1) agonist- in murine primary microglia, organotypic hippocampal slice cultures (OHSCs) and human primary monocytes. Results demonstrate that cap (0.1-25 µM) significantly (p < 0.05) inhibited the release of prostaglandin E2 (PGE2), 8-iso-PGF2α, and differentially regulated the levels of cytokines (TNF-α, IL-6 & IL-1ß). Pharmacological blockade (via capsazepine & SB366791) and genetic deficiency of TRPV1 (TRPV1-/-) did not prevent cap-mediated suppression of PGE2 in activated microglia and OHSCs. Inhibition of PGE2 was partially dependent on the reduced levels of PGE2 synthesising enzymes, COX-2 and mPGES-1. To evaluate potential molecular targets, we discovered that cap significantly suppressed the activation of p38 MAPK and MAPKAPK2 (MK2). Altogether, we demonstrate that cap alleviates excessive inflammatory events by targeting the PGE2 pathway in in vitro and ex vivo immune cell models. These findings have broad relevance in understanding and paving new avenues for ongoing TRPV1 based drug therapies in neuroinflammatory-associated diseases.

Rice bran derivatives alleviate microglia activation: possible involvement of MAPK pathway.

BACKGROUND: Hyperactivation of microglia is considered to be a key hallmark of brain inflammation and plays a critical role in regulating neuroinflammatory events. Neuroinflammatory responses in microglia represent one of the major risk factors for various neurodegenerative diseases. One of the strategies to protect the brain and slow down the progression of these neurodegenerative diseases is by consuming diet enriched in anti-oxidants and polyphenols. Therefore, the present study aimed to evaluate the anti-inflammatory effects of rice bran extract (RBE), one of the rich sources of vitamin E forms (tocopherols and tocotrienols) and gamma-oryzanols, in primary rat microglia. METHODS: The vitamin E profile of the RBE was quantified by high-performance liquid chromatography (HPLC). Microglia were stimulated with lipopolysaccharide (LPS) in the presence or absence of RBE. Release of prostaglandins (prostaglandin (PG) E2, 8-iso-prostaglandin F2α (8-iso-PGF2α)) were determined with enzyme immunoassay (EIA). Protein levels and genes related to PGE2 synthesis (Cyclooxygenase-2 (COX-2), microsomal prostaglandin E synthase-1 (mPGES-1)) and various pro- and anti-inflammatory cytokines (TNF-α, IL-1ß, IL-6, and IL-10), were assessed by western blot, ELISA, and quantitative real-time PCR. Furthermore, to elucidate the molecular targets of RBE, the phosphorylated state of various mitogen-activated protein kinase (MAPK) signaling molecules (p38 MAPK, ERK 1/2, and JNK) and activation of NF-kB pathway was studied. RESULTS: RBE significantly inhibited the release of PGE2 and free radical formation (8-iso-PGF2α) in LPS-activated primary microglia. Inhibition of PGE2 by RBE was dependent on reduced COX-2 and mPGES-1 immunoreactivity in microglia. Interestingly, treatment of activated microglia with RBE further enhanced the gene expression of the microglial M2 marker IL-10 and reduced the expression of pro-inflammatory M1 markers (TNF-α, IL-1ß). Further mechanistic studies showed that RBE inhibits microglial activation by interfering with important steps of MAPK signaling pathway. Additionally, microglia activation with LPS leads to IkB-α degradation which was not affected by the pre-treatment of RBE. CONCLUSIONS: Taken together, our data demonstrate that RBE is able to affect microglial activation by interfering in important inflammatory pathway. These in vitro findings further demonstrate the potential value of RBE as a nutraceutical for the prevention of microglial dysfunction related to neuroinflammatory diseases, including Alzheimer's disease.

Inhibition of Neuroinflammation in LPS-Activated Microglia by Cryptolepine.

Cryptolepine, an indoloquinoline alkaloid in Cryptolepis sanguinolenta, has anti-inflammatory property. In this study, we aimed to evaluate the effects of cryptolepine on lipopolysaccharide (LPS)- induced neuroinflammation in rat microglia and its potential mechanisms. Microglial activation was induced by stimulation with LPS, and the effects of cryptolepine pretreatment on microglial activation and production of proinflammatory mediators, PGE2/COX-2, microsomal prostaglandin E2 synthase and nitric oxide/iNOS were investigated. We further elucidated the role of Nuclear Factor-kappa B (NF- κ B) and the mitogen-activated protein kinases in the antiinflammatory actions of cryptolepine in LPS-stimulated microglia. Our results showed that cryptolepine significantly inhibited LPS-induced production of tumour necrosis factor-alpha (TNF α ), interleukin-6 (IL-6), interleukin-1beta (IL-1 ß ), nitric oxide, and PGE2. Protein and mRNA levels of COX-2 and iNOS were also attenuated by cryptolepine. Further experiments on intracellular signalling mechanisms show that I κ B-independent inhibition of NF- κ B nuclear translocation contributes to the anti-neuroinflammatory actions of cryptolepine. Results also show that cryptolepine inhibited LPS-induced p38 and MAPKAPK2 phosphorylation in the microglia. Cell viability experiments revealed that cryptolepine (2.5 and 5 µ M) did not produce cytotoxicity in microglia. Taken together, our results suggest that cryptolepine inhibits LPS-induced microglial inflammation by partial targeting of NF- κ B signalling and attenuation of p38/MAPKAPK2.

Anti-neuroinflammatory properties of synthetic cryptolepine in human neuroblastoma cells: possible involvement of NF-κB and p38 MAPK inhibition.

Cryptolepis sanguinolenta and its bioactive alkaloid, cryptolepine have shown anti-inflammatory activity. However, the underlying mechanism of anti-inflammatory action in neuronal cells has not been investigated. In the present study we evaluated an extract of C. sanguinolenta (CSE) and cryptolepine (CAS) on neuroinflammation induced with IL-1ß in SK-N-SH neuroblastoma cells. We then attempted to elucidate the mechanisms underlying the anti-neuroinflammatory effects of CAS in SK-N-SH cells. Cells were stimulated with 10 U/ml of IL-1ß in the presence or absence of different concentrations of CSE (25-200 µg/ml) and CAS (2.5-20 µM). After 24 h incubation, culture media were collected to measure the production of PGE2 and the pro-inflammatory cytokines (TNFα and IL-6). Protein and gene expressions of cyclooxygenase (COX-2) and microsomal prostaglandin synthase-1 (mPGES-1) were studied by immunoblotting and qPCR, respectively. CSE produced significant (p < 0.05) inhibition of TNFα, IL-6 and PGE2 production in SK-N-SH cells. Studies on CAS showed significant and dose-dependent inhibition of TNFα, IL-6 and PGE2 production in IL-1ß-stimulated cells without affecting viability. Pre-treatment with CAS (10 and 20 µM) was also found to inhibit IL-1ß-induced protein and gene expressions of COX-2 and mPGES-1. Further studies to determine the mechanism of action of CAS showed inhibition of NF-κBp65 nuclear translocation, but not IκB phosphorylation. At 10 and 20 µM, CAS inhibited IL-1ß-induced phosphorylation of p38 MAPK. Studies on the downstream substrate of p38, MAPK-activated protein kinase 2 (MAPKAPK2) showed that CAS produced significant (p < 0.05) and dose dependent inhibition of MAPKAPK2 phosphorylation in IL-1ß-stimulated SK-N-SH cells. This study clearly shows that cryptolepine (CAS) inhibits neuroinflammation through mechanisms involving inhibition of COX-2 and mPGES-1. It is suggested that these actions are probably mediated through NF-κB and p38 signalling.

Effects of diet and/or exercise in enhancing spinal cord sensorimotor learning.

Given that the spinal cord is capable of learning sensorimotor tasks and that dietary interventions can influence learning involving supraspinal centers, we asked whether the presence of omega-3 fatty acid docosahexaenoic acid (DHA) and the curry spice curcumin (Cur) by themselves or in combination with voluntary exercise could affect spinal cord learning in adult spinal mice. Using an instrumental learning paradigm to assess spinal learning we observed that mice fed a diet containing DHA/Cur performed better in the spinal learning paradigm than mice fed a diet deficient in DHA/Cur. The enhanced performance was accompanied by increases in the mRNA levels of molecular markers of learning, i.e., BDNF, CREB, CaMKII, and syntaxin 3. Concurrent exposure to exercise was complementary to the dietary treatment effects on spinal learning. The diet containing DHA/Cur resulted in higher levels of DHA and lower levels of omega-6 fatty acid arachidonic acid (AA) in the spinal cord than the diet deficient in DHA/Cur. The level of spinal learning was inversely related to the ratio of AA:DHA. These results emphasize the capacity of select dietary factors and exercise to foster spinal cord learning. Given the non-invasiveness and safety of the modulation of diet and exercise, these interventions should be considered in light of their potential to enhance relearning of sensorimotor tasks during rehabilitative training paradigms after a spinal cord injury.

The anti-inflammatory effects of the 5-HT3 receptor antagonist tropisetron are mediated by the inhibition of p38 MAPK activation in primary human monocytes.

BACKGROUND: There is evidence from human and animal research that 5-hydroxytryptamine (5-HT) 3 receptor antagonists, particularly tropisetron, exert analgesic and anti-inflammatory activity. We have demonstrated that tropisetron inhibited lipopolysaccharide (LPS)-stimulated tumor necrosis factor (TNF)alpha and interleukin-(IL-)1beta release in primary human monocytes. The underlying mechanisms of these effects have not been investigated in detail so far. METHODS: The molecular mechanisms of the anti-inflammatory effects of tropisetron were investigated in human primary monocytes in vitro by studying IL-1beta and TNFalpha mRNA levels by PCR and reporter gene assay and by elucidating the phosphorylation of p38 mitogen activated kinase (MAPK) by Western blot. RESULTS: The steady state levels of IL-1beta and TNFalpha mRNA in LPS-activated human peripheral monocytes and the transcriptional activity of the TNFalpha promoter were not inhibited by tropisetron, suggesting that the inhibitory activity of this 5-HT3 receptor antagonist takes place at the post-transcriptional level. Additionally, we found that tropisetron prevents the phosphorylation and thus activation of the p38 MAPK, which is involved in post-transcriptional regulation of various cytokines. CONCLUSION: Our data indicate that the anti-inflammatory effects of the 5-HT3 receptor antagonist tropisetron, as shown in vivo, are possibly mediated by a selective inhibition of pro-inflammatory cytokines at the post-transcriptional level. 5-HT3 receptor antagonists are therefore a new and promising therapeutic option. New and more selective--in respect to the 5-HT3 subtypes--5-HT3R antagonists might be a future perspective in the pharmacological treatment of inflammatory diseases.

Pharmacological inhibition of Akt and downstream pathways modulates the expression of COX-2 and mPGES-1 in activated microglia.

BACKGROUND: Microglia are considered a major target for modulating neuroinflammatory and neurodegenerative disease processes. Upon activation, microglia secrete inflammatory mediators that contribute to the resolution or to further enhancement of damage in the central nervous system (CNS). Therefore, it is important to study the intracellular pathways that are involved in the expression of the inflammatory mediators. Particularly, the role of the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) and glycogen synthase kinase-3 (GSK-3) pathways in activated microglia is unclear. Thus, in the present study we investigated the role of Akt and its downstream pathways, GSK-3 and mTOR, in lipopolysaccharide (LPS)-activated primary rat microglia by pharmacological inhibition of these pathways in regard to the expression of cyclooxygenase (COX)-2 and microsomal prostaglandin E synthase-1 (mPGES-1) and to the production of prostaglandin (PG) E2 and PGD2. FINDINGS: We show that inhibition of Akt by the Akt inhibitor X enhanced the production of PGE2 and PGD2 without affecting the expression of COX-2, mPGES-1, mPGES-2 and cytosolic prostaglandin E synthase (cPGES). Moreover, inhibition of GSK-3 reduced the expression of both COX-2 and mPGES-1. In contrast, the mTOR inhibitor rapamycin enhanced both COX-2 and mPGES-1 immunoreactivity and the release of PGE2 and PGD2. Interestingly, NVP-BEZ235, a dual PI3K/mTOR inhibitor, enhanced COX-2 and reduced mPGES-1 immunoreactivity, albeit PGE2 and PGD2 levels were enhanced in LPS-stimulated microglia. However, this compound also increased PGE2 in non-stimulated microglia. CONCLUSION: Taken together, we demonstrate that blockade of mTOR and/or PI3K/Akt enhances prostanoid production and that PI3K/Akt, GSK-3 and mTOR differently regulate the expression of mPGES-1 and COX-2 in activated primary microglia. Therefore, these pathways are potential targets for the development of novel strategies to modulate neuroinflammation.

Resveratrol inhibits prostaglandin formation in IL-1beta-stimulated SK-N-SH neuronal cells.

Resveratrol, a polyphenol present in grapes and red wine, has been studied due to its vast pharmacological activity. It has been demonstrated that resveratrol inhibits production of inflammatory mediators in different in vitro and in vivo models. Our group recently demonstrated that resveratrol reduced the production of prostaglandin (PG) E2 and 8-isoprostane in rat activated microglia. In a microglial-neuronal coculture, resveratrol reduced neuronal death induced by activated microglia. However, less is known about its direct roles in neurons. In the present study, we investigated the effects of resveratrol on interleukin (IL)-1beta stimulated SK-N-SH cells. Resveratrol (0.1-5 microM) did not reduce the expression of cyclooxygenase (COX)-2 and microsomal PGE2 synthase-1 (mPGES-1), although it drastically reduced PGE2 and PGD2 content in IL-1beta-stimulated SK-N-SH cells. This effect was due, in part, to a reduction in COX enzymatic activity, mainly COX-2, at lower doses of resveratrol. The production of 8-iso-PGF2alpha, a marker of cellular free radical generation, was significantly reduced by resveratrol. The present work provides evidence that resveratrol reduces the formation of prostaglandins in neuroblastoma cells by reducing the enzymatic activity of inducible enzymes, such as COX-2, and not the transcription of the PG synthases, as demonstrated elsewhere.

Mangiferin inhibits cyclooxygenase-2 expression and prostaglandin E2 production in activated rat microglial cells.

Mangiferin, a naturally occurring glucosylxanthone, has potent antioxidant and anti-inflammatory properties, as demonstrated in several reports. However, very limited information is available on the effects of this natural polyphenol on microglial activation. Thus, the aim of this study was to examine whether mangiferin is able to reduce prostaglandin E(2) (PGE(2)) and 8-iso-prostaglandin F(2alpha) (8-iso-PGF(2alpha)) production by lipopolysaccharide (LPS)-activated primary rat microglia. Microglial cells were stimulated with 10ng/ml of LPS in the presence or absence of different concentrations of mangiferin (1-50 microM). After 24h incubation, culture media were collected to measure the production of PGE(2) and 8-iso-PGF(2alpha) using enzyme immunoassays. Protein levels of cyclooxygenase (COX)-1 and COX-2 were studied by immunoblotting after 24h of incubation with LPS. Mangiferin potently reduced LPS-induced PGE(2) synthesis and the formation of 8-iso-PGF(2alpha). Interestingly, mangiferin dose-dependently reduced LPS-induced COX-2 protein synthesis without modifying COX-2 transcription. This was due to a decrease in COX-2 transcript stability. However, mangiferin did not modify LPS-mediated phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK), a key factor involved in enhancing COX-2 mRNA stability and COX-2 translation in primary microglia. Mangiferin had no effects on LPS-induced expression of inducible nitric oxide synthase (iNOS) or TNF-alpha production. Taken together, results from the present study indicate that mangiferin is able to limit microglial activation, in terms of attenuation of PGE(2) production, free radical formation and reduction in COX-2 synthesis induced by LPS. These data suggest that modulation of microglial activation might contribute to the mechanism of cerebral protection by mangiferin.

Regulation of prostaglandin E2 synthase expression in activated primary rat microglia: evidence for uncoupled regulation of mPGES-1 and COX-2.

Prostaglandin E2 (PGE2) is among the most important mediators involved in neuroinflammatory processes. The final step of its synthesis is regulated by enzymes termed prostaglandin E2 synthases (PGES). Three PGES are known, cytosolic (c)PGES, membrane-associated (m)PGES-1 and mPGES-2. The expression of mPGES-1 is induced by inflammatory stimuli such as lipopolysaccharide (LPS), interleukin (IL)-1beta, and tumor necrosis factor (TNF)-alpha. Although some roles of mPGES-1 have already been suggested, its function in the CNS and the signaling pathways involved in its upregulation are poorly understood. In this study, we examined the regulation of mPGES-1 in primary rat microglia and the signaling pathways involved in its expression. Whereas the expression of cPGES and mPGES-2 was not stimulated by LPS, low doses of LPS (0.1-1 ng/mL) sufficiently stimulated mPGES-1 mRNA expression. A corresponding protein synthesis, however, was obtained only with higher doses (10-100 ng/mL). The LPS-induced increase of mPGES-1 was inhibited by different signaling pathway inhibitors, such as SP600125, LY294002, GF109203X, and SC-514, suggesting the involvement of c-Jun N-terminal kinase (JNK), phosphatidylinositol 3-kinase (PI-3K)/Akt, protein kinase C (PKC) pathways, and the nuclear factor (NF)-kappaB, respectively. In contrast to other reports, LPS-induced mPGES-1 synthesis was not invariably coupled to the synthesis of COX-2, since inhibition of PI-3K with LY294002 decreased mPGES-1 but increased COX-2 levels. This detailed view of the intracellular signaling pathways involved in mPGES-1 expression in activated microglia opens a new avenue in the search for novel potential therapeutic targets to reduce neuroinflammation, and demonstrates that mPGES-1 expression is not strictly coupled to the expression of COX-2.

Resveratrol potently reduces prostaglandin E2 production and free radical formation in lipopolysaccharide-activated primary rat microglia.

BACKGROUND: Neuroinflammatory responses are triggered by diverse ethiologies and can provide either beneficial or harmful results. Microglial cells are the major cell type involved in neuroinflammation, releasing several mediators, which contribute to the neuronal demise in several diseases including cerebral ischemia and neurodegenerative disorders. Attenuation of microglial activation has been shown to confer protection against different types of brain injury. Recent evidence suggests that resveratrol has anti-inflammatory and potent antioxidant properties. It has been also shown that resveratrol is a potent inhibitor of cyclooxygenase (COX)-1 activity. Previous findings have demonstrated that this compound is able to reduce neuronal injury in different models, both in vitro and in vivo. The aim of this study was to examine whether resveratrol is able to reduce prostaglandin E2 (PGE2) and 8-iso-prostaglandin F2alpha (8-iso-PGF2 alpha) production by lipopolysaccharide (LPS)-activated primary rat microglia. METHODS: Primary microglial cell cultures were prepared from cerebral cortices of neonatal rats. Microglial cells were stimulated with 10 ng/ml of LPS in the presence or absence of different concentrations of resveratrol (1-50 microM). After 24 h incubation, culture media were collected to measure the production of PGE2 and 8-iso-PGF2 alpha using enzyme immunoassays. Protein levels of COX-1, COX-2 and microsomal prostaglandin E synthase-1 (mPGES-1) were studied by Western blotting after 24 h of incubation with LPS. Expression of mPGES-1 at the mRNA level was investigated using reverse transcription-polymerase chain reaction (RT-PCR) analysis. RESULTS: Our results indicate that resveratrol potently reduced LPS-induced PGE2 synthesis and the formation of 8-iso-PGF2 alpha, a measure of free radical production. Interestingly, resveratrol dose-dependently reduced the expression (mRNA and protein) of mPGES-1, which is a key enzyme responsible for the synthesis of PGE2 by activated microglia, whereas resveratrol did not affect the expression of COX-2. Resveratrol is therefore the first known inhibitor which specifically prevents mPGES-1 expression without affecting COX-2 levels. Another important observation of the present study is that other COX-1 selective inhibitors (SC-560 and Valeroyl Salicylate) potently reduced PGE2 and 8-iso-PGF2 alpha production by LPS-activated microglia. CONCLUSION: These findings suggest that the naturally occurring polyphenol resveratrol is able to reduce microglial activation, an effect that might help to explain its neuroprotective effects in several in vivo models of brain injury.

Ascorbic acid enhances the inhibitory effect of aspirin on neuronal cyclooxygenase-2-mediated prostaglandin E2 production.

Inhibition of neuronal cyclooxygenase-2 (COX-2) and hence prostaglandin E2 (PGE2) synthesis by non-steroidal anti-inflammatory drugs has been suggested to protect neuronal cells in a variety of pathophysiological situations including Alzheimer's disease and ischemic stroke. Ascorbic acid (vitamin C) has also been shown to protect cerebral tissue in a variety of experimental conditions, which has been attributed to its antioxidant capacity. In the present study, we show that ascorbic acid dose-dependently inhibited interleukin-1beta (IL-1beta)-mediated PGE2 synthesis in the human neuronal cell line, SK-N-SH. Furthermore, in combination with aspirin, ascorbic acid augmented the inhibitory effect of aspirin on PGE2 synthesis. However, ascorbic acid had no synergistic effect along with other COX inhibitors (SC-58125 and indomethacin). The inhibition of IL-1beta-mediated PGE2 synthesis by ascorbic acid was not due to the inhibition of the expression of COX-2 or microsomal prostaglandin E synthase (mPGES-1). Rather, ascorbic acid dose-dependently (0.1-100 microM) produced a significant reduction in IL-1beta-mediated production of 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha), a reliable indicator of free radical formation, suggesting that the effects of ascorbic acid on COX-2-mediated PGE2 biosynthesis may be the result of the maintenance of the neuronal redox status since COX activity is known to be enhanced by oxidative stress. Our results provide in vitro evidence that the neuroprotective effects of ascorbic acid may depend, at least in part, on its ability to reduce neuronal COX-2 activity and PGE2 synthesis, owing to its antioxidant properties. Further, these experiments suggest that a combination of aspirin with ascorbic acid constitutes a novel approach to render COX-2 more sensitive to inhibition by aspirin, allowing an anti-inflammatory therapy with lower doses of aspirin, thereby avoiding the side effects of the usually high dose aspirin treatment.