Insoluble matrix components of glioma cells suppress LPS-mediated iNOS/NO induction in microglia

Anti-inflammatory effect of Ailanthus altissima (Mill.) Swingle leaves in lipopolysaccharide-stimulated astrocytes

ETHNOPHARMACOLOGICAL RELEVANCE

Activated astrocytes are involved in the progression of neurodegenerative diseases. Traditionally, Ailanthus altissima (Mill.) Swingle, widely distributed in East Asia, has been used as a medicine for the treatment of fever, gastric diseases, and inflammation. Although A. altissima has been reported to play an anti-inflammatory role in peripheral tissues or cells, its role in the central nervous system (CNS) remains unclear.

AIM OF THE STUDY

In the present study, we investigated the anti-inflammatory effects and mechanism of action of A. altissima in primary astrocytes stimulated by lipopolysaccharide (LPS).

MATERIALS AND METHODS

A nitrite assay was used to measure nitric oxide (NO) production, and the tetrazolium salt 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay was performed to determine cytotoxicity. The expression levels of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and mitogen-activated protein kinase (MAPK) were determined with western blotting. Reverse-transcription PCR was used to assess the expression of inflammatory cytokines. The levels of reactive oxygen species were measured using 2,7-dichlorodihydrofluorescein diacetate. Luciferase assay and immunocytochemistry were used for assessing nuclear factor-kappa B (NF-κB) transcription and p65 localization, respectively. Memory and social interaction were analyzed using the Y-maze and three-chamber tests, respectively.

RESULTS

The ethanol extract of A. altissima leaves (AAE) inhibited iNOS and COX-2 expression in LPS-stimulated astrocytes. Moreover, AAE reduced the transcription of various proinflammatory mediators, hindered NF-κB activation, and suppressed extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) activation without p38 activation. Ultra-high performance liquid chromatography with mass spectrometry analysis revealed that AAE comprised ethyl gallate, quercetin, and kaempferol, along with luteolin, which has anti-inflammatory properties, and repressed LPS-induced nitrite levels and the nuclear translocation of p65. Finally, oral administration of AAE attenuated LPS-induced memory and social impairment in mice and repressed LPS-induced ERK and JNK activation in the cortices of mice.

CONCLUSION

AAE could have therapeutic uses in the treatment of neuroinflammatory diseases via suppression of astrocyte activation.

Protective Role of Natural Products in Glioblastoma Multiforme: A Focus on Nitric Oxide Pathway

In spite of therapeutic modalities such as surgical resection, chemotherapy, and radiotherapy, Glioblastoma Multiforme (GBM) remains an incurable fatal disease. This necessitates further therapeutic options that could enhance the efficacy of existing modalities. Nitric Oxide (NO), a short-lived small molecule, has been revealed to play a crucial role in the pathophysiology of GBM. Several studies have demonstrated that NO is involved in apoptosis, metastasis, cellular proliferation, angiogenesis, invasion, and many other processes implicated in GBM pathobiology. Herein, we elaborate on the role of NO as a therapeutic target in GBM and discuss some natural products affecting the NO signaling pathway.

Nitric oxide attenuates microglia proliferation by sequentially facilitating calcium influx through TRPV2 channels, activating NFATC2, and increasing p21 transcription

Microglia proliferation is critical for proper development and function of the central nervous system (CNS), while dysregulation of proliferation contributes to pathology. We recently reported that male inducible nitric oxide synthase knockout (iNOS^-/-) mice displayed significantly more proliferating microglia in their postnatal cortex than age-matched wildtype (WT) male mice. Moreover, nitric oxide (NO) signaling in mouse microglia greatly upregulates calcium entry through transient receptor potential vanilloid type 2 (TRPV2) channels. Considering that TRPV2 activity restricts astrocytic proliferation within glioma tissues, we investigated the roles of iNOS/NO signaling and TRPV2 expression in the regulation of microglial proliferation in vitro using assays of calcium imaging, immunocytochemistry, western blot, and polymerase chain reaction. Results showed that non-dividing microglia exhibited substantially higher expression of TRPV2 on the plasma membrane and significantly larger calcium influx through TRPV2 channels in comparison to dividing microglia. Additionally, non-dividing WT microglia exhibited significantly more NO production than dividing WT microglia. Furthermore, the NO-donor NOC18 increased the nuclear translocation of nuclear factor of activated T-cells cytoplasmic 2 (NFATC2) and the mRNA of the cyclin-dependent kinase inhibitor p21 and decreased the percentage of dividing WT and iNOS^-/- microglia in culture. Importantly, the presence of the TRPV2 inhibitor tranilast abolished these effects of NOC18. Together, results from this study indicated that iNOS/NO signaling inhibits microglial proliferation through TRPV2-mediated calcium influx, nuclear translocation of the transcription factor NFATC2, and p21 expression. [Figure: see text].

Anti‑inflammatory role of Prunus persica L. Batsch methanol extract on lipopolysaccharide‑stimulated glial cells

Glial cells are the resident immune cells of the central nervous system. Reactive glial cells release inflammatory mediators that induce neurotoxicity or aggravate neurodegeneration. Regulation of glial activation is crucial for the initiation and progression of neuropathological conditions. Constituents of the peach tree (Prunus persica L. Batsch), which has a global distribution, have been found to exert therapeutic effects in pathological conditions, such as rashes, eczema and allergies. However, the therapeutic potential of its aerial parts (leaves, fruits and twigs) remains to be elucidated. The present study aimed to evaluate the anti-inflammatory role of P. persica methanol extract (PPB) on lipopolysaccharide (LPS)-stimulated glial cells. High-performance liquid chromatography coupled with tandem mass spectrometry analysis showed that PPB contained chlorogenic acid and catechin, which have antioxidant properties. Western blot and reverse transcription polymerase chain reaction results indicated that PPB reduced the transcription of various proinflammatory enzymes (nitric oxide synthase and cyclooxygenase-2) and cytokines [tumor necrosis factor-α, interleukin (IL)-1β and IL-6] in LPS-stimulated BV2 cells. In addition, PPB inhibited the activation of NF-κB and various mitogen-activated protein kinases required for proinflammatory mediator transcription. Finally, nitrite measurement and immunocytochemistry results indicated that PPB also suppressed nitrite production and NF-κB translocation in LPS-stimulated primary astrocytes. Thus, PPB may be used as a potential therapeutic agent for neurodegenerative diseases and neurotoxicity via the suppression of glial cell activation.

Tumor-derived fibulin-3 activates pro-invasive NF-κB signaling in glioblastoma cells and their microenvironment

Molecular profiling of glioblastomas has revealed the presence of key signaling hubs that contribute to tumor progression and acquisition of resistance. One of these main signaling mechanisms is the NF-κB pathway, which integrates multiple extracellular signals into transcriptional programs for tumor growth, invasion, and maintenance of the tumor-initiating population. We show here that an extracellular protein released by glioblastoma cells, fibulin-3, drives oncogenic NF-κB in the tumor and increases NF-κB activation in peritumoral astrocytes. Fibulin-3 expression correlates with a NF-κB-regulated “invasive signature” linked to poorer survival, being a possible tissue marker for regions of active tumor progression. Accordingly, fibulin-3 promotes glioblastoma invasion in a manner that requires NF-κB activation both in the tumor cells and their microenvironment. Mechanistically, we found that fibulin-3 activates the metalloprotease ADAM17 by competing with its endogenous inhibitor, TIMP3. This results in sustained release of soluble TNFα by ADAM17, which in turn activates TNF receptors and canonical NF-κB signaling. Taken together, our results underscore fibulin-3 as a novel extracellular signal with strong activating effect on NF-κB in malignant gliomas. Because fibulin-3 is produced de novo in these tumors and is absent from normal brain we propose that targeting the fibulin-3/NF-κB axis may provide a novel avenue to disrupt oncogenic NF-κB signaling in combination therapies for malignant brain tumors.

Depletion of GSH in glial cells induces neurotoxicity: relevance to aging and degenerative neurological diseases

Oxidative stress induced by inhibition of glutathione (GSH) biosynthesis with D,L-buthionine-S,R-sulfoximine (BSO) causes human microglia, human astrocytes, THP-1 cells, and U373 cells to secrete materials toxic to human neuroblastoma SH-SY5Y cells and stimulates them to release TNF-alpha, IL-6, and nitrite ions. The effect is correlated with activation of the inflammatory pathways P38 MAP- kinase, Jun-N-terminal kinase, and NF-kappaB. The effect is reduced by adding to the medium GSH or clotrimazole (CTM), an inhibitor of Ca(2+)-influx through TRPM2 channels. It is also produced by inhibiting TRPM2 protein expression in microglia and astrocytes through introduction of its small inhibitory RNA (siRNA). TRPM2 mRNA is expressed by glial cells but not by SH-SY5Y cells. BSO in the culture medium causes an almost 3-fold increase in [Ca(2+)](i) in microglia and astrocytes over a 24-h period, which is reduced to half by the addition of CTM. The data strongly suggest that inhibiting intracellular GSH synthesis induces a neuroinflammatory response in human microglia and astrocytes, which is linked to Ca(2+) influx through TRPM2 channels. It represents a new model for inducing neuroinflammation and suggests that increasing GSH levels in glial cells may confer neuroprotection in neurodegenerative diseases, such as Alzheimer disease, which have a prominent neuroinflammatory component.

Hydrogen sulfide attenuates lipopolysaccharide-induced inflammation by inhibition of p38 mitogen-activated protein kinase in microglia

The present study attempts to investigate the effect of H(2)S on lipopolysaccharide (LPS)-induced inflammation in both primary cultured microglia and immortalized murine BV-2 microglial cells. We found that exogenous application of sodium hydrosulfide (NaHS) (a H(2)S donor, 10-300 micro mol/L) attenuated LPS-stimulated nitric oxide (NO) in a concentration-dependent manner. Stimulating endogenous H(2)S production decreased LPS-stimulated NO production, whereas lowering endogenous H(2)S level increased basal NO production. Western blot analysis showed that both exogenous and endogenous H(2)S significantly attenuated the stimulatory effect of LPS on inducible nitric oxide synthase expression, which is mimicked by SB 203580, a specific p38 mitogen-activated protein kinase (MAPK) inhibitor. Exogenously applied NaHS significantly attenuated LPS-induced p38 MAPK phosphorylation in BV-2 microglial cells. Moreover, both NaHS (300 micro mol/L) and SB 203580 (1 micro mol/L) significantly attenuated LPS-induced tumor necrosis factor-alpha secretion, another inflammatory indicator. In addition, NaHS (10-300 micro mol/L) dose-dependently decreased LPS-stimulated NO production in primary cultured astrocytes, suggesting that the anti-neuroinflammatory effect of H(2)S is not specific to microglial cells alone. Taken together, H(2)S produced an anti-inflammatory effect in LPS-stimulated microglia and astrocytes, which may be due to inhibition of inducible nitric oxide synthase and p38 MAPK signaling pathways. These findings may have important implications in the treatment of neuroinflammation-related diseases.