Forsythiaside A Exhibits Anti-inflammatory Effects in LPS-Stimulated BV2 Microglia Cells Through Activation of Nrf2/HO-1 Signaling Pathway

Inflammation and oxidative stress have been reported to play critical roles in the pathogenesis of neurodegenerative disease. Forsythiaside A, a phenylethanoside product isolated from air-dried fruits of Forsythia suspensa, has been reported to have anti-inflammatory and antioxidant effects. In this study, the anti-inflammatory effects of forsythiaside A on LPS-stimulated BV2 microglia cells and primary microglia cells were investigated. The production of inflammatory mediators TNF-α, IL-1β, NO and PGE₂ were detected in this study. NF-κB, nuclear factor-erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1) expression were detected by western blot analysis. Our results showed that forsythiaside A significantly inhibited LPS-induced inflammatory mediators TNF-α, IL-1β, NO and PGE₂ production. LPS-induced NF-κB activation was suppressed by forsythiaside A. Furthermore, forsythiaside A was found to up-regulate the expression of Nrf2 and HO-1. In conclusion, this study demonstrates that forsythiaside A inhibits LPS-induced inflammatory responses in BV2 microglia cells and primary microglia cells through inhibition of NF-κB activation and activation of Nrf2/HO-1 signaling pathway.     

Anti-neuroinflammatory Effect of Emodin in LPS-Stimulated Microglia: Involvement of AMPK/Nrf2 Activation

AMPK/Nrf2 signaling regulates multiple antioxidative factors and exerts neuroprotective effects. Emodin is one of the main bioactive components extracted from Polygonum multiflorum, a plant possessing important activities for human health and for treating a variety of diseases. This study examined whether emodin can activate AMPK/Nrf2 signaling and induce the expression of genes targeted by this pathway. In addition, the anti-neuroinflammatory properties of emodin in lipopolysaccharide (LPS)-stimulated microglia were examined. In microglia, the emodin treatment increased the levels of LKB1, CaMKII, and AMPK phosphorylation. Emodin increased the translocation and transactivity of Nrf2 and enhanced the levels of HO-1 and NQO1. In addition, the emodin-mediated expression of HO-1 and NQO1 was attenuated completely by an AMPK inhibitor (compound C). Moreover, emodin decreased dramatically the LPS-induced production of NO and PGE₂ as well as the protein expression and promoter activity of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). In addition, emodin effectively inhibited the production of pro-inflammatory cytokines, TNF-α and IL-6, and reduced the level of IκBα phosphorylation, leading to the suppression of the nuclear translocation, phosphorylation, and transactivity of NF-κB. Emodin also suppressed the LPS-stimulated activation of STATs, JNK, and p38 MAPK. The anti-inflammatory effects of emodin were reversed by transfection with Nrf-2 and HO-1 siRNA and by a co-treatment with an AMPK inhibitor. These results suggest that emodin isolated from P. multiflorum can be used as a natural anti-neuroinflammatory agent that exerts its effects by inducing HO-1 and NQO1 via AMPK/Nrf2 signaling in microglia.     

Sulforaphane attenuates hepatic fibrosis via NF-E2-related factor 2-mediated inhibition of transforming growth factor-β/Smad signaling

Sulforaphane (SFN) is a dietary isothiocyanate that exerts chemopreventive effects via NF-E2-related factor 2 (Nrf2)-mediated induction of antioxidant/phase II enzymes, such as heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoreductase 1 (NQO1). This work was undertaken to evaluate the effects of SFN on hepatic fibrosis and profibrotic transforming growth factor (TGF)-β/Smad signaling, which are closely associated with oxidative stress. SFN suppressed TGF-β-enhanced expression of α-smooth muscle actin (α-SMA), a marker of hepatic stellate cell (HSC) activation, and profibrogenic genes such as type I collagen, fibronectin, tissue inhibitor of matrix metalloproteinase (TIMP)-1, and plasminogen activator inhibitor (PAI)-1 in hTERT, an immortalized human HSC line. SFN inhibited TGF-β-stimulated activity of a PAI-1 promoter construct and (CAGA)(9) MLP-Luc, an artificial Smad3/4-specific reporter, in addition to reducing phosphorylation and nuclear translocation of Smad3. Nrf2 overexpression was sufficient to inhibit the TGF-β/Smad signaling and PAI-1 expression. Conversely, knockdown of Nrf2, but not inhibition of HO-1 or NQO1 activity, significantly abolished the inhibitory effect of SFN on (CAGA)(9) MLP-Luc activity. However, inhibition of NQO1 activity reversed repression of TGF-β-stimulated expression of type I collagen by SFN, suggesting the involvement of antioxidant activity of SFN in the suppression of Smad-independent fibrogenic gene expression. Finally, SFN treatment attenuated the development and progression of early stage hepatic fibrosis induced by bile duct ligation in mice, accompanied by reduced expression of type I collagen and α-SMA. Collectively, these results show that SFN elicits an antifibrotic effect on hepatic fibrosis through Nrf2-mediated inhibition of the TGF-β/Smad signaling and subsequent suppression of HSC activation and fibrogenic gene expression.     

Genipin up-regulates heme oxygenase-1 via PI3-kinase-JNK1/2-Nrf2 signaling pathway to enhance the anti-inflammatory capacity in RAW264.7 macrophages

Genipin, an aglycon of geniposide, has been reported to exhibit diverse pharmacological functions such as antitumor and anti-inflammatory effects. This study aimed to elucidate the anti-inflammatory mechanism of genipin, focusing particularly on the role of heme oxygenase-1 (HO-1), a potent anti-inflammatory enzyme. In RAW264.7 cells, genipin increased HO-1 expression and its enzyme activity via a NF-E2-related factor 2 (Nrf2)–antioxidant response element (ARE) pathway. These effects were significantly inhibited by exposure to the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor, LY294002, or by expression of a dominant negative mutant of PI 3-kinase. Additional experiments showed that the activation of c-Jun NH₂-terminal kinase 1/2 (JNK1/2) is required for genipin-induced phosphorylation and nuclear translocation of Nrf2 and antioxidant response element (ARE)-driven induction of HO-1, and acts as a downstream effector of PI 3-kinase. Furthermore, functional significance of HO-1 induction was revealed by genipin-mediated inhibition of lipopolysaccharide-stimulated inducible nitric oxide synthase expression or cyclooxygenase-2 promoter activity, the response was reversed by the blocking of HO-1 protein synthesis or HO-1 enzyme activity. Therefore, identification of PI 3-kinase-JNK1/2-Nrf2-linked signaling cascade in genipin-mediated HO-1 expression defines the signaling event that could participate in genipin-mediated anti-inflammatory response.     

Screening active components of modified Xiaoyao powder as NRF2 agonists

Nuclear factor (erythroid‐derived 2)‐like 2 (NRF2) regulates antioxidant enzymes and phase II detoxifying enzymes, such as NAD(P)H: quinone oxidoreductase 1 (NQO1). Modified Xiaoyao powder (MXP) is most frequently used in the prevention and treatment of breast cancer in China. This study aimed to screen active components of MXP for antioxidant stress and chemoprevention, which depend on NRF2‐NQO1 signalling pathway. A total of 25 monomeric compounds contained in MXP were screened using an antioxidant response element–luciferase reporter. The most potent antioxidant response element–luciferase inducers were chosen to further examine their effects on NRF2 and NQO1 in MCF‐7 cells. These results were then confirmed by determining the oxidative stress levels and chemopreventive effect on inhibiting carcinogenesis transformation in NRF2 knockdown (NRF2^KD) and NRF2 wild‐type MCF‐10A cells. We found that quercetin, kaempferol, and atractylenolide II in MXP were potent NRF2 inducers, which could up‐regulate the expression of NRF2 and its downstream enzymes NQO1. In addition, these components could decrease reduced oxidative stress and inhibit carcinogenesis transformation, which depended on NRF2‐NQO1 pathway. In conclusion, NRF2‐NQO1 pathway plays an essential role in mediating the activity of MXP and its active components, at least in part; some beneficial effects of MXP may be applicable to breast cancer chemoprevention. Our study firstly found MXP active components including quercetin, kaempferol, and atractylenolide II. Our results firstly demonstrate that NRF2‐NQO1 pathway plays an essential role in mediating the activity of MXP and its active components in breast cancer chemoprevention. Our study firstly found that atractylenolide II is a novel NRF2 inducer.     

LL202 ameliorates colitis against oxidative stress of macrophage by activation of the Nrf2/HO-1 pathway

LL202, a newly synthesized flavonoid derivative, has been confirmed to inhibit the mitogen-activated protein kinase pathway and activation protein-1 activation in monocytes; however, the anti-inflammatory mechanism has not been clearly studied. Uncontrolled overproduction of reactive oxygen species (ROS) has involved in oxidative damage of inflammatory bowel disease. In this study, we investigated that LL202 reduced lipopolysaccharide (LPS)-induced ROS production and malondialdehyde levels and increased superoxide dismutase, glutathione, and total antioxidant capacity in RAW264.7 cells. Mechanically, LL202 could upregulate heme oxygenase-1 (HO-1) via promoting nuclear translocation of nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) to regulate LPS-induced oxidative stress in macrophages. In vivo, we validated the role of LL202 in dextran sulfate sodium- and TNBS-induced colitis models, respectively. The results showed that LL202 decreased the proinflammatory cytokine expression and regulated colonic oxidative stress by activating the Nrf2/HO-1 pathway. In conclusion, our study showed that LL202 exerts an anti-inflammatory effect by enhancing the antioxidant capacity of the Nrf2/HO-1 pathway to macrophages.     

Genipin Inhibits LPS-Induced Inflammatory Response in BV2 Microglial Cells

Genipin, an aglycon of geniposide, has been reported to have anti-inflammatory effect. However, the anti-inflammatory activity of genipin on LPS-stimulated BV2 microglial cells has not been reported. In this study, we investigated the molecular mechanisms responsible for the anti-inflammatory activity of genipin both in vivo and in vitro. The levels of TNF-α, IL-1β, NO and PGE₂ were detected by ELISA. The expression of Nrf2, HO-1, and NF-κB were detected by western blot analysis. In vivo, genipin significantly attenuated LPS-induced memory deficit in the Morris water maze and passive avoidance tasks. Genipin also inhibited LPS-induced TNF-α and IL-1β expression in brain tissues. In vitro, our results showed that genipin inhibited LPS-induced TNF-α, IL-1β, NO and PGE₂ production in a concentration-dependent manner. Genipin also suppressed LPS-induced NF-κB activation. In addition, the expression of Nrf2 and HO-1 were up-regulated by treatment of genipin. Furthermore, the inhibition of genipin on inflammatory mediator production was attenuated by transfection with Nrf2 siRNA. In conclusion, genipin inhibited LPS-induced inflammatory response by activating Nrf2 signaling pathway in BV2 microglia.     

Naringenin Exerts Anti-inflammatory Effects in Paraquat-Treated SH-SY5Y Cells Through a Mechanism Associated with the Nrf2/HO-1 Axis

Naringenin (NGN; 5,7-dihydroxy-2-(4-hydroxyphenyl)-2,3-dihydrochromen-4-one; C₁₅H₁₂O₅), a flavanone, is found in citrus fruits and has been viewed as an antioxidant and anti-inflammatory agent. NGN is a potent inducer of the nuclear factor erythroid 2-related factor 2 (Nrf2) and upregulates the expression of heme oxygenase-1 (HO-1), an enzyme exhibiting both antioxidant and anti-inflammatory effects. The complete mechanism by which NGN exerts anti-inflammatory actions is not completely understood yet. Therefore, we investigated here whether NGN would be able to reduce the inflammation induced by paraquat (PQ) in SH-SY5Y cells. Additionally, we analyzed the mechanism associated with the NGN-induced anti-inflammatory effect. We found that a pretreatment with NGN at 80 µM for 2 h decreased the levels of pro-inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in PQ-treated SH-SY5Y cells. The production of nitric oxide (NO^·) and levels of cyclooxygenase-2 (COX-2) and of the inducible isoform of nitric oxide synthase (iNOS) were downregulated by NGN in the cells exposed to PQ. Moreover, NGN downregulated the activation of the nuclear factor-κB (NF-κB) in PQ-treated cells. The anti-apoptotic and anti-inflammatory effects promoted by NGN were abolished by ZnPP IX (a specific inhibitor of HO-1) or by knockdown of Nrf2 by small interfering RNA (siRNA). Therefore, NGN induced anti-inflammatory effects in PQ-treated SH-SY5Y cells by a mechanism associated with the Nrf2/HO-1 signaling pathway.