Suppression of LPS-induced inflammatory responses by inflexanin B in BV2 microglial cells

Effect of Luteolin and Apigenin on the Production of Il-31 and Il-33 in Lipopolysaccharides-Activated Microglia Cells and Their Mechanism of Action

Microglia cells are resident cells of the central nervous system (CNS) charged with modulating inflammation in the CNS. Overstimulation of microglia cells continuously releases inflammatory mediators that contribute to neurodegenerative diseases. Apigenin and Luteolin are flavonoids with reported anti-inflammatory activities. However, their effects on IL-31 and IL-33 production in microglial cells are unknown. Here, we investigated the effects of apigenin and luteolin on the production of IL-31 and IL-33 by microglia cells. SIM-A9 microglial cells were pre-treated with apigenin or luteolin and stimulated with lipopolysaccharides to evaluate the production of IL-31 and IL-33. The study revealed that apigenin and luteolin inhibited the production of IL-31 and IL-33 at the gene and protein expressions and the secretion levels. Using potent inhibitors of MAPK, NF-κB, and STAT3 signaling pathways, we demonstrated that apigenin and luteolin’s suppression of ERK and JNK contributed to the inhibition of IL-31 and IL-33 in the MAPK pathway. Luteolin’s suppression of NF-κB and STAT3 also contributed to the inhibition of IL-31 and IL-33. Further analysis revealed that both compounds prevented nuclear translocation of activated NF-κB and STAT3, an act that subsequently prevented their DNA binding activities. Collectively, the study suggested that apigenin and luteolin’s regulation of signaling pathways contributed to the inhibition of IL-31 and IL-33, thus suggesting its importance for the improvement of neurodegenerative diseases involving these two cytokines.

Magnesium Lithospermate B Suppresses Lipopolysaccharide-Induced Neuroinflammation in BV2 Microglial Cells and Attenuates Neurodegeneration in Lipopolysaccharide-Injected Mice

Chronic inflammation in the brain plays a critical role in major neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). Microglia, the resident macrophages and intrinsic components of the central nervous system (CNS), appear to be the main effectors in this pathological process. Magnesium lithospermate B (MLB) is one of the major bioactive components of Radix Salviae miltiorrhizae, which has been documented to protect neurons against multiple types of neuronal injury. However, its functions on microglia and the related neuroinflammation remain unknown. In the present study, BV2 microglial cells were used to assess the anti-neuroinflammatory capacity of MLB. Our data show that treatment with MLB could not only suppress lipopolysaccharide (LPS)-induced proliferation and morphological changes, but also interfere with cell cycle progression in BV2 cells. More strikingly, it attenuated the production of the inflammatory mediator nitric oxide (NO) and a panel of pro-inflammatory cytokine in LPS-stimulated BV2 cells, including tumor necrosis factor-α (TNF-α), interleukin (IL)-1α, IL-1β, and IL-6, and also promoted a phenotypic switch from the M1 to the M2 phenotype. Additionally, an in vivo study showed that the administration of MLB could ameliorate lipopolysaccharide-induced neurodegeneration and microglial activation in the hippocampus of adult mice. Mechanistically, MLB blocked the activation of the NF-κB pathway upon LPS stimulation, indicating that the effects of MLB on microglia may be mediated by the NK-κB pathway. These results suggest the therapeutic potential of MLB as a novel anti-inflammatory and microglia-modulating drug for neurodegenerative diseases.

RNA sequencing reveals resistance of TLR4 ligand-activated microglial cells to inflammation mediated by the selective jumonji H3K27 demethylase inhibitor

Persistent microglial activation is associated with the production and secretion of various pro-inflammatory genes, cytokines and chemokines, which may initiate or amplify neurodegenerative diseases. A novel synthetic histone 3 lysine 27 (H3K27) demethylase JMJD3 inhibitor, GSK-J4, was proven to exert immunosuppressive activities in macrophages. However, a genome-wide search for GSK-J4 molecular targets has not been undertaken in microglia. To study the immuno-modulatory effects of GSK-J4 at the transcriptomic level, triplicate RNA sequencing and quantitative real-time PCR analyses were performed with resting, GSK-J4-, LPS- and LPS + GSK-J4-challenged primary microglial (PM) and BV-2 microglial cells. Among the annotated genes, the transcriptional sequencing of microglia that were treated with GSK-J4 revealed a selective effect on LPS-induced gene expression, in which the induction of cytokines/chemokines, interferon-stimulated genes, and prominent transcription factors TFs, as well as previously unidentified genes that are important in inflammation was suppressed. Furthermore, we showed that GSK-J4 controls are important inflammatory gene targets by modulating STAT1, IRF7, and H3K27me3 levels at their promoter sites. These unprecedented results demonstrate that the histone demethylase inhibitor GSK-J4 could have therapeutic applications for neuroinflammatory diseases.

Extracts of Actinidia arguta stems inhibited LPS-induced inflammatory responses through nuclear factor-κB pathway in Raw 264.7 cells

The inflammatory response protects our body from bacteria and tumors, but chronic inflammation driven by the persistent activation of macrophages can lead to serious adverse effects including gastrointestinal problems, cardiac disorders, and a sore throat. Part of the ongoing research is focused on searching for antiinflammatory compounds from natural sources, so we investigated the effects of hardy kiwis (Actinidia arguta, Lauraceae) stems on inflammation induced by lipopolysaccharide (LPS) in Raw 264.7 cells to test the hypothesis that antiinflammatory effects of A. arguta stems were exerted through the inhibition of the nuclear factor (NF)-κB pathway. The methanol extract of A. arguta (20 μg/mL) stems lowered nitric oxide production in LPS-stimulated Raw 264.7 cells by 40%. It was then partitioned with hexane, chloroform, ethyl acetate, butanol, and water based on the polarity of each compound. Among the 5 layers, the chloroform layer had the greatest inhibitory effect on LPS-stimulated nitric oxide production and inducible nitric oxide synthase mRNA expression in Raw 264.7 cells. However, the levels of prostaglandin E2 and cyclooxygease 2 were not altered. On the other hand, treatment of cells with the chloroform layer of A. arguta before LPS stimulation also reduced them RNA expression of proinflammatory cytokines including tumor necrosis factor α and interleukin 1β. Nuclear translocation of NF-κB p50 and p65 subunits induced by LPS was also inhibited by treatment with the chloroform layer of A. arguta. This was accompanied with the reduced phosphorylation of mitogen-activated protein kinases including extracellular signal-regulated protein kinase 1/2, c-Jun N-terminal protein kinase, and p38. Taken together, these results suggest that chloroform layer of A. arguta exerted antiinflammatory effects by the inhibition of mitogen-activated protein kinase phosphorylation and nuclear translocation of NF-κB.

IRAK1/4-targeted anti-inflammatory action of caffeic acid

Caffeic acid (CA) is a phenolic compound that is frequently present in fruits, grains, and dietary supplements. Although CA has been reported to display various biological activities such as anti-inflammatory, anti-cancer, anti-viral, and anti-oxidative effects, the action mechanism of CA is not yet fully elucidated. In this study, the anti-inflammatory action mechanism of CA was examined in lipopolysaccharide (LPS) treated macrophages (RAW264.7 cells) and HCl/EtOH-induced gastritis. CA was found to diminish nitric oxide (NO) and prostaglandin E₂ (PGE₂) production in LPS-stimulated RAW264.7 cells. Additionally, mRNA levels of tumor necrosis factor (TNF)-α, cyclooxygenase (COX)-2, and inducible NO synthase (iNOS) were downregulated by CA. CA also strongly suppressed the nuclear translocation of AP-1 family proteins and the related upstream signaling cascade composed of interleukin-1 receptor-associated kinase 1 (IRAK1), IRAK4, TGF-β-activated kinase 1 (TAK1), mitogen-activated protein kinase kinase 4/7 (MKK4/7), and c-Jun N-terminal kinase (JNK). In a direct kinase assay, CA was revealed to directly inhibit IRAK1 and IRAK4. CA also ameliorated HCl/EtOH-induced gastric symptoms via the suppression of JNK, IRAK1, and IRAK4. Therefore, our data strongly suggest that CA acts as an anti-inflammatory drug by directly suppressing IRAK1 and IRAK4.