The green tea polyphenol (-)-epigallocatechin-3-gallate inhibits leukocyte activation by bacterial formylpeptide through the receptor FPR

[Tea polyphenols ameliorates acute lung injury in septic mice by inhibiting NLRP3 inflammasomes]

OBJECTIVE

To investigate the mechanism of tea polyphenols (TP) for regulating NLRP3 inflammasomes and alleviating acute lung injury in septic mice.

METHODS

Sixty C57BL/6 mice were randomly assigned into sham-operated, cecal ligation and puncture (CLP) and CLP +TP treatment groups, and survival of the mice was recorded after modeling in each group. The lung wet/dry weight ratio and myeloperoxidase (MPO) activity were determined, and lung injury of the mice was evaluated using HE staining and acute lung injury score. The expressions of IL-1β, TNF-α, IL-6, NLRP3, caspase-1 p10, ASC, MPO, and caspase-8 in the lung tissue were detected using ELISA, Western blotting, or immunohistochemical staining. MDA and H2O2 levels in the lungs were detected to evaluate the level of oxidative stress. Immunofluorescence assay was used to investigate the co-localization of NLRP3 and NOX4.

RESULTS

The postoperative mortality rate at 72 h, lung wet/dry weight ratio, MPO level and acute lung injury scores were significantly lower in CLP+TP group than in CLP group (P < 0.05). Treatment with TP significantly reduced the expressions of NLRP3-related inflammatory factors (P < 0.05) and lowered MDA and H2O2 levels in the lung tissue of the septic mice (P < 0.05). Immunofluorescence co-staining showed a lower level of NOX4 and NLRP3 co-localization in CLP+TP group than in CLP group.

CONCLUSION

TP inhibits NLRP3 inflammasome-associated inflammation to alleviate CLP-induced acute lung injury in mice through a regulatory mechanism that inhibits NOX4 expression and reduces oxidative stress in the lung tissue.

Antimicrobial Effect of Tea Polyphenols against Foodborne Pathogens: A Review

ABSTRACT

Food contamination by foodborne pathogens is still widespread in many countries around the world, and food safety is a major global public health issue. Therefore, novel preservatives that can guarantee safer food are in high demand. Contrary to artificial food preservatives, tea polyphenols (TPs) are getting wide attention as food additives for being "green," "safe," and "healthy." TPs come from many sources, and the purification technology is sophisticated. Compared with other natural antibacterial agents, the antibacterial effect of TPs is more stable, making them excellent natural antibacterial agents. This review includes a systematic summary of the important chemical components of TPs and the antibacterial mechanisms of TPs against various foodborne pathogens. The potential applications of TPs are also discussed. These data provide a theoretical basis for the in-depth study of TPs.

HIGHLIGHTS

Dietary supplementation with green tea extract promotes enhanced human leukocyte activity

BACKGROUND

Leukocytes play a vital role in the host defence and inflammatory systems, the latter being responsible for the pathogenesis of a wide spectrum of acute and chronic diseases. Green tea is a popular beverage, which is consumed worldwide and its active ingredients are epicatechin derivatives, which possess distinct anti-inflammatory properties. The purpose of this study was to investigate if a green tea extract could enhance leukocyte function in humans.

METHODS

Volunteers were asked to take 300 mg of the green tea extract daily for 14 days and the capacity of circulating leukocytes to release both myeloperoxidase and lactoferrin was assessed. Whole blood from volunteers was stimulated with the bacterial peptide Formyl-Methionine-Leucine-Phenylalanine (fMet-Leu-Phe). Myeloperoxidase an enzyme that converts hydrogen peroxide to hypochlorous acid and is stored and secreted from the granules of neutrophils and monocytes and was measured as well as lactoferrin which is an iron-binding protein stored and secreted from the neutrophils. In conjunction the antioxidant capacity of the blood of the volunteers was also determined using a chemiluminescence method that measures the capacity of plasma to scavenge superoxide.

RESULTS

After 14 days of treatment there was a significant increase in the release of myeloperoxidase and lactoferrin when whole blood was stimulated with fMet-Leu-Phe (p<0.05), which activates a number of leukocytes including mature neutrophils and monocytes. This was mirrored by a significant increase in the total antioxidant status after 14 days of green tea ingestion (p0.05). After the "wash-out" period of 4 weeks, all parameters were consistent with those observed at the start of the trial (day 0). Treatment with the green tea extract also caused a slight but non-significant decrease in the number of circulating leukocytes, but the counts remained within published "normal" ranges for healthy human adults.

CONCLUSIONS

This study indicates that a green tea extract when taken as a dietary supplement for 14 days can increase the leukocyte activity and the total plasma antioxidant status and may have role to play in the prevention of inflammatory disease.

Formylpeptide receptor 1 mediates the tumorigenicity of human hepatocellular carcinoma cells

G protein-coupled chemoattractant receptors (GPCRs) have been implicated in cancer progression. Formylpeptide receptor 1 (FPR1) was originally identified as a GPCR mediating anti-microbial host defense. However, the role of FPR1 in tumorigenesis remains poorly understood. The current study aims to investigate the potential of FPR1 to regulate human hepatoma growth and invasion. We found the FPR1 gene and protein expression in human intratumoral and peritumoral tissues of hepatocellular carcinoma (HCC) specimens and in human hepatoma cell lines. FPR1 activation mediated the migration, calcium mobilization and ERK-dependent IL-8 production by hepatic cancer cells. FPR1 knockdown substantially reduced the tumorigenicity of hepatoma cells in nude mice. Necrotic hepatic tumor cells released factor(s) that activated FPR1 in live tumor cells. Our results indicate a critical role of FPR1 in the progression of malignant human hepatic cancer. FPR1 thus may represent a molecular target for the development of novel anti-hepatoma therapeutics.

Functional characterization of ferret CCL20 and CCR6 and identification of chemotactic inhibitors

CCL20 is currently the only known chemokine ligand for the receptor CCR6, and is a mucosal chemokine involved in normal and pathological immune responses. Although nucleotide sequence data are available for ccl20 and ccr6 sequences from multiple species, the ferret ccl20 and ccr6 sequences have not been determined. To increase our understanding of immune function in ferret models of infection and vaccination, we have used RT-PCR to obtain the ferret ccl20 and ccr6 cDNA sequences and functionally characterize the encoded proteins. The open reading frames of both genes were highly conserved across species and mostly closely related to canine sequences. For functional analyses, single cell clones expressing ferret CCR6 were generated, a ferret CCL20/mouse IgG(2a) fusion protein (fCCL20-mIgG(2a)) was produced, and fCCL20 was chemically synthesized. Cell clones expressing ferret CCR6 responded chemotactically to fCCL20-mIgG2a fusion protein and synthetic ferret CCL20. Chemotaxis inhibition studies identified the polyphenol epigallocatechin-3-gallate and the murine γ-herpesvirus 68 M3 protein as inhibitors of fCCL20. Surface plasmon resonance studies revealed that EGCG bound directly to fCCL20. These results provide molecular characterization of previously unreported ferret immune gene sequences and for the first time identify a broad-spectrum small molecule inhibitor of CCL20 and reveal CCL20 as a target for the herpesviral M3 protein.

EGCG stimulates autophagy and reduces cytoplasmic HMGB1 levels in endotoxin-stimulated macrophages

Historically, consumption of Green tea (Camellia sinensis) has been associated with health benefits against multiple diseases including cancer, atherosclerosis and cardiovascular disorders. Emerging evidence has suggested a pathogenic role for HMGB1, a newly identified "late" mediator of lethal systemic inflammation, in the aforementioned diseases. Here we demonstrated that a major ingredient of Green tea, EGCG, was internalized into HMGB1-containing LC3-positive cytoplasmic vesicles (likely autophagosomes) in macrophages, and induced HMGB1 aggregation in a time-dependent manner. Furthermore, EGCG stimulated LC3-II production and autophagosome formation, and inhibited LPS-induced HMGB1 up-regulation and extracellular release. The EGCG-mediated HMGB1 inhibitory effects were diminished by inhibition of class III phosphatidylinositol-3 kinase (with 3-methyladenine) or knockdown of an essential autophagy-regulating protein, beclin-1. Moreover, the EGCG-mediated protection against lethal sepsis was partly impaired by co-administration of an autophagy inhibitor, chloroquine. Taken together, the present study has suggested a possibility that EGCG inhibits HMGB1 release by stimulating its autophagic degradation.

Epigallocatechin-3-gallate reduces airway inflammation in mice through binding to proinflammatory chemokines and inhibiting inflammatory cell recruitment

One major activity of chemokines is the recruitment of immune cells to sites of infection and inflammation. CD4(+) Th1 cells play critical roles in host defense against pathogens and in the pathogenesis of many immune-mediated diseases. It was reported that epigallocatechin-3-gallate (EGCG) exhibits anti-inflammatory properties, but the mechanisms have not been completely defined. In this study, we found that EGCG markedly decreased recruitment of murine OVA-specific Th1 cells and other inflammatory cells into the airways in a Th1 adoptive-transfer mouse model. In vitro analysis revealed that EGCG inhibited CXCR3 ligand-driven chemotaxis of murine and human cells. Surface plasmon resonance studies revealed that EGCG bound directly to chemokines CXCL9, CXCL10, and CXCL11. These results indicated that one anti-inflammatory mechanism of EGCG is binding of proinflammatory chemokines and limiting their biological activities. These findings support further development of EGCG as a potent therapeutic for inflammatory diseases.

HCV peptide (C5A), an amphipathic α-helical peptide of hepatitis virus C, is an activator of N-formyl peptide receptor in human phagocytes

The hepatitis C virus (HCV) nonstructural 5A, a phosphorylated zinc metalloprotein, is an essential component of the HCV replication complex. An amphipathic α-helical peptide (HCV peptide [C5A]) derived from nonstructural 5A membrane anchor domain possesses potent anti-HCV and anti-HIV activity in vitro. In this study, we aimed to investigate the potential of HCV peptide (C5A) to regulate host immune responses. The capacity of HCV peptide (C5A) in vitro to induce migration and calcium mobilization of human phagocytes and chemoattractant receptor-transfected cells was investigated. The recruitment of phagocytes in vivo induced by HCV peptide (C5A) and its adjuvant activity were examined. The results revealed that HCV peptide (C5A) was a chemoattractant and activator of human phagocytic leukocytes by using a G-protein coupled receptor, namely formyl peptide receptor. In mice, HCV peptide (C5A) induced massive phagocyte infiltration after injection in the air pouch or the s.c. region. HCV peptide (C5A) also acted as an immune adjuvant by enhancing specific T cell responses to Ag challenge in mice. Our results suggest that HCV peptide (C5A) derived from HCV regulates innate and adaptive immunity in the host by activating the formyl peptide receptor.

Norepinephrine promotes microglia to uptake and degrade amyloid beta peptide through upregulation of mouse formyl peptide receptor 2 and induction of insulin-degrading enzyme

Locus ceruleus (LC) is the main subcortical site of norepinephrine synthesis. In Alzheimer's disease (AD) patients and rodent models, degeneration of LC neurons and reduced levels of norepinephrine in LC projection areas are significantly correlated with the increase in amyloid plaques, neurofibrillary tangles, and severity of dementia. Activated microglia play a pivotal role in the progression of AD by either clearing amyloid beta peptide (Abeta) deposits through uptake of Abeta or releasing cytotoxic substances and proinflammatory cytokines. Here, we investigated the effect of norepinephrine on Abeta uptake and clearance by murine microglia and explored the underlying mechanisms. We found that murine microglia cell line N9 and primary microglia expressed beta(2) adrenergic receptor (AR) but not beta(1) and beta(3)AR. Norepinephrine and isoproterenol upregulated the expression of Abeta receptor mFPR2, a mouse homolog of human formyl peptide receptor FPR2, through activation of beta(2)AR in microglia. Norepinephrine also induced mFPR2 expression in mouse brain. Activation of beta(2)AR in microglia promoted Abeta(42) uptake through upregulation of mFPR2 and enhanced spontaneous cell migration but had no effect on cell migration in response to mFPR2 agonists. Furthermore, activation of beta(2)AR on microglia induced the expression of insulin-degrading enzyme and increased the degradation of Abeta(42). Mechanistic studies showed that isoproterenol induced mFPR2 expression through ERK1/2-NF-kappaB and p38-NF-kappaB signaling pathways. These findings suggest that noradrenergic innervation from LC is needed to maintain adequate Abeta uptake and clearance by microglia, and norepinephrine is a link between neuron and microglia to orchestrate the host response to Abeta in AD.

Resveratrol differentially modulates inflammatory responses of microglia and astrocytes

BACKGROUND

Inflammatory responses in the CNS mediated by activated glial cells play an important role in host-defense but are also involved in the development of neurodegenerative diseases. Resveratrol is a natural polyphenolic compound that has cardioprotective, anticancer and anti-inflammatory properties. We investigated the capacity of resveratrol to protect microglia and astrocyte from inflammatory insults and explored mechanisms underlying different inhibitory effects of resveratrol on microglia and astrocytes.

METHODS

A murine microglia cell line (N9), primary microglia, or astrocytes were stimulated by LPS with or without different concentrations of resveratrol. The expression and release of proinflammatory cytokines (TNF-alpha, IL-1beta, IL-6, MCP-1) and iNOS/NO by the cells were measured by PCR/real-time PCR and ELISA, respectively. The phosphorylation of the MAP kinase superfamily was analyzed by western blotting, and activation of NF-kappaB and AP-1 was measured by luciferase reporter assay and/or electrophoretic mobility shift assay.

RESULTS

We found that LPS stimulated the expression of TNF-alpha, IL-1beta, IL-6, MCP-1 and iNOS in murine microglia and astrocytes in which MAP kinases, NF-kappaB and AP-1 were differentially involved. Resveratrol inhibited LPS-induced expression and release of TNF-alpha, IL-6, MCP-1, and iNOS/NO in both cell types with more potency in microglia, and inhibited LPS-induced expression of IL-1beta in microglia but not astrocytes. Resveratrol had no effect on LPS-stimulated phosphorylation of ERK1/2 and p38 in microglia and astrocytes, but slightly inhibited LPS-stimulated phosphorylation of JNK in astrocytes. Resveratrol inhibited LPS-induced NF-kappaB activation in both cell types, but inhibited AP-1 activation only in microglia.

CONCLUSION

These results suggest that murine microglia and astrocytes produce proinflammatory cytokines and NO in response to LPS in a similar pattern with some differences in signaling molecules involved, and further suggest that resveratrol exerts anti-inflammatory effects in microglia and astrocytes by inhibiting different proinflammatory cytokines and key signaling molecules.

Effects of (-)-epigallocatechin gallate on RPE cell migration and adhesion

PURPOSE

In diseases such as proliferative vitreoretinopathy (PVR), proliferative diabetic retinopathy (PDR), and age-related macular degeneration (AMD), retinal pigment epithelial (RPE) cells can initiate proliferation and migration and secrete extracellular matrix (ECM) proteins. (-)-Epigallocatechin gallate (EGCG)-a natural anti-oxidant flavonoid that is abundant in green tea-has been shown to suppress the migration and adhesion of many cell types, but its effects on RPE cell migration and adhesion were unknown. Several studies have shown that platelet-derived growth factor (PDGF) enhances proliferation and migration effects on RPE cells in PVR, and that fibronectin is a major ECM component of PVR tissue. Therefore, we investigated the inhibitory effects of EGCG on RPE cell migration induced by PDGF-BB, an isoform of PDGF, and adhesion by fibronectin.

METHODS

The migration of RPE cells was detected by an electric cell-substrate impedance sensing (ECIS) migration assay and a Transwell migration assay. Cells were loaded with 2',7'-bis-(carboxyethyl)-5(6')-carboxyfluorescein acetoxymethyl ester (BCECF/AM), and their adhesion to fibronectin was examined. The interactions of EGCG with PDGF-BB were analyzed by a dot binding assay. Cytoskeletal reorganization was examined by immunofluorescence microscopy. The PDGF-BB-induced signaling pathways were detected by western blotting.

RESULTS

In the present study, we find that EGCG can inhibit PDGF-BB-induced human RPE cell migration and, in a dose-dependent manner, RPE cell adhesion to fibronectin. Our analysis demonstrates that EGCG does not directly bind to PDGF-BB and the inhibition of EGCG against fibronectin-induced cytoskeletal reorganization is observed. Furthermore, EGCG is shown to suppress PDGF-BB-induced PDGF-beta receptors, downstream PI3K/Akt, and MAPK phosphorylation.

CONCLUSIONS

Our results provide the first evidence that EGCG is an effective inhibitor of RPE cell migration and adhesion to fibronectin and, therefore, may prevent epiretinal membrane formation.

Epigallocatechin-3-gallate (EGCG) attenuates inflammation in MRL/lpr mouse mesangial cells

Epigallocatechin-3-gallate (EGCG), a bioactive component of green tea, has been reported to exert anti-inflammatory effects on immune cells. EGCG is also shown to activate the metabolic regulator, adenosine 5'-monophosphate-activated protein kinase (AMPK). Reports have also indicated that EGCG inhibits the immune-stimulated phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway. The PI3K/Akt/mTOR pathway has been implicated in mesangial cell activation in lupus. Mesangial cells from MRL/lpr lupus-like mice are hyper-responsive to immune stimulation and overproduce nitric oxide (NO) and other inflammatory mediators when stimulated. In our current studies, we sought to determine the mechanism by which EGCG attenuates immune-induced expression of pro-inflammatory mediators. Cultured mesangial cells from MRL/lpr mice were pre-treated with various concentrations of EGCG and stimulated with lipopolysaccharide (LPS)/interferon (IFN)-gamma. EGCG activated AMPK and blocked LPS/IFN-gamma-induced inflammatory mediator production (iNOS expression, supernatant NO and interleukin-6). Interestingly, EGCG attenuated inflammation during AMPK inhibition indicating that the anti-inflammatory effect of EGCG may be partially independent of AMPK activation. Furthermore, we found that EGCG effectively inhibited the immune-stimulated PI3K/Akt/mTOR pathway independently of AMPK, by decreasing phosphorylation of Akt, suggesting an alternate mechanism for EGCG-mediated anti-inflammatory action in mesangial cells. Taken together, these studies show that EGCG attenuated inflammation in MRL/lpr mouse mesangial cells via the PI3K/Akt/mTOR pathway. Our findings suggest a potential therapeutic role for the use of EGCG to regulate inflammation and control autoimmune disease.

Sesamin inhibits bacterial formylpeptide-induced inflammatory responses in a murine air-pouch model and in THP-1 human monocytes

The reaction of human leukocytes to chemoattractants is an important component of the host immune response and also plays a crucial role in the development of inflammation. Sesamin has been shown to inhibit lipid peroxidation and regulate cytokine production. In this study, we examined the effect of sesamin on inflammatory responses elicited by the bacterial chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLF) in vitro and in vivo and explored the mechanisms involved. fMLF is recognized by a human G protein-coupled receptor formyl peptide receptor (FPR) on phagocytic leukocytes. Sesamin at concentrations between 12.5 and 50 micromol/L inhibited fMLF-induced chemotaxis of human monocyte cell line THP-1 differentiated with dibutyryl cyclic AMP (P < 0.01). Similarly, sesamin inhibited FPR-transfected rat basophilic leukemia cell [epitope-tagged human FPR (ETFR) cell] migration toward fMLF (P < 0.01). In fMLF-induced inflammation in a murine air-pouch model, intraperitoneal administration of sesamin (12 mgkg(-1)d(-1) for 2 d) suppressed leukocyte infiltration into the air pouch induced by fMLF [(62.89 +/- 7.93) x 10(4) vs. (19.67 +/- 4.43) x 10(4) cells/air pouch; n = 9; P < 0.001]. Ca(2+) mobilization and mitogen-activated protein kinase extracellular signal-regulated kinase (ERK1/2) activation are involved in fMLF-induced leukocyte migration. Pretreatment of ETFR cells with sesamin inhibited fMLF-induced ERK1/2 phosphorylation in a dose-dependent manner but did not affect fMLF-induced Ca(2+) flux. Electrophoretic mobility shift assay showed that pretreatment of THP-1 cells with sesamin dose dependently inhibited fMLF-induced nuclear factor-kappaB (NF-kappaB) activation. These results suggest that sesamin inhibits leukocyte activation by fMLF through ERK1/2- and NF-kappaB-related signaling pathways and thus is a potential compound for the management of inflammatory diseases.