Naringenin, one of the most abundant flavonoids in citrus, grapefruits and tomatoes, has been used as a traditional anti-inflammatory agent for centuries. However, the molecular mechanism of naringenin in intestinal inflammation remains unknown so far. The present study investigated a molecular basis for the protective effect of naringenin in dextran sulphate Sodium-induced murine colitis. Pre-administration of naringenin significantly reduced the severity of colitis and resulted in down-regulation of pro-inflammatory mediators (inducible NO synthase (iNOS), intercellular adhesion molecule-1 (ICAM-1), monocyte chemoattractant protein-1 (MCP-1), cyclo-oxygenase-2 (Cox2), TNF-α and IL-6 mRNA) in the colon mucosa. The decline in the production of pro-inflammatory cytokines, specifically TNF-α and IL-6, correlated with a decrease in mucosal Toll-like receptor 4 (TLR4) mRNA and protein. Phospho-NF-κB p65 protein was significantly decreased, which correlated with a similar decrease in phospho-IκBα protein. Consistent with the in vivo results, naringenin exposure blocked lipopolysaccharide-stimulated nuclear translocation of NF-κB p65 in mouse macrophage RAW264.7 cells. In addition, in vitro NF-κB reporter assays performed on human colonic HT-29 cells exposed to naringenin demonstrated a significant inhibition of TNF-α-induced NF-κB luciferase expression. Thus, for the first time, the present study indicates that targeted inhibition of the TLR4/NF-κB signalling pathway might be an important mechanism for naringenin in abrogating experimental colitis.

Paeonia lactiflora Pall is one of the most well-known herbs in China, Korea, and Japan for more than 1,200 years. Paeoniflorin, the major bioactive component of peony root, has recently been reported to have anticolitic activity. However, the underlying molecular mechanism is unclear. The present study was to explore the possible mechanism of paeoniflorin in attenuating dextran sulfate sodium (DSS)-induced colitis. Pre- and coadministration of paeoniflorin significantly reduced the severity of colitis and resulted in downregulation of several inflammatory parameters in the colon, including the activity of myeloperoxidase (MPO), the levels of TNF-α and IL-6, and the mRNA expression of proinflammatory mediators (MCP-1, Cox2, IFN-γ, TNF-α, IL-6, and IL-17). The decline in the activation of NF-κB p65, ERK, JNK, and p38 MAPK correlated with a decrease in mucosal Toll-like receptor 4 (TLR4) but not TLR2 or TLR5 expression. In accordance with the in vivo results, paeoniflorin downregulated TLR4 expression, blocked nuclear translocation of NF-κB p65, and reduced the production of IL-6 in LPS-stimulated mouse macrophage RAW264.7 cells. Transient transfection assay performed in LPS-stimulated human colon cancer HT-29 cells indicated that paeoniflorin inhibits NF-κB transcriptional activity in a dose-dependent manner. TLR4 knockdown and overexpression experiments demonstrated a requirement for TLR4 in paeoniflorin-mediated downregulation of inflammatory cytokines. Thus, for the first time, the present study indicates that paeoniflorin abrogates DSS-induced colitis via decreasing the expression of TLR4 and suppressing the activation of NF-κB and MAPK pathways.

Inflammatory bowel disease (IBD) is a chronic and relapsing inflammatory disorder of the gastrointestinal (GI) tract, and currently no curative treatment available. Mangiferin, a natural glucosylxanthone mainly from the fruit, leaves and stem bark of the mango tree, has strong anti-inflammatory activity. We sought to investigate whether mangiferin attenuates inflammation in a mouse model of chemically induced IBD. Pre-administration of mangiferin significantly attenuated dextran sulfate sodium (DSS)-induced body weight loss, diarrhea, colon shortening and histological injury, which correlated with the decline in the activity of myeloperoxidase (MPO) and the level of tumor necrosis factor-α (TNF-α) in the colon. DSS-induced degradation of inhibitory κBα (IκBα) and the phosphorylation of nuclear factor-kappa B (NF-κB) p65 as well as the mRNA expression of pro-inflammatory mediators (inducible NO synthase (iNOS), intercellular adhesion molecule-1 (ICAM-1), TNF-α, interleukin-1β (IL-1β) and IL-6) in the colon were also downregulated by mangiferin treatment. Additionally, the phosphorylation/activation of DSS-induced mitogen-activated protein kinase (MAPK) proteins was also inhibited by mangiferin treatment. In accordance with the in vivo results, mangiferin exposure blocked TNF-α-stimulated nuclear translocation of NF-κB in RAW264.7 mouse macrophage cells. Transient transfection gene reporter assay performed in TNF-α-stimulated HT-29 human colorectal adenocarcinoma cells indicated that mangiferin inhibits NF-κB transcriptional activity in a dose-dependent manner. The current study clearly demonstrates a protective role for mangiferin in experimental IBD through NF-κB and MAPK signaling inhibition. Since mangiferin is a natural compound with little toxicity, the results may contribute to the effective utilization of mangiferin in the treatment of human IBD.

Targeted activation of pregnane X receptor (PXR) in recent years has become a therapeutic strategy for inflammatory bowel disease. Chrysin is a naturally occurring flavonoid with antiinflammation activity. The current study investigated the role of chrysin as a putative mouse PXR agonist in preventing experimental colitis. Pre-administration of chrysin ameliorated inflammatory symptoms in mouse models of colitis (dextran sodium sulfate-and 2,4,6-trinitrobenzene sulfonic acid-induced) and resulted in down-regulation of nuclear transcription factor kB (NF-kB) target genes (inducible NO synthase, intercellular adhesion molecule-1, monocyte chemotactic protein-1, cyclooxygenase 2, tumor necrosis factor-a, and interleukin 6) in the colon mucosa. Chrysin inhibited the phosphorylation/degradation of inhibitor kBa (IkBa), which correlated with the decrease in the activity of myeloperoxidase and the levels of tumor necrosis factor-a and interleukin 6 in the colon. Consistent with the in vivo results, chrysin blocked lipopolysaccharide -stimulated nuclear translocation of NF-kB p65 in mouse macrophage RAW264.7. Furthermore, chrysin dose-dependently activated human/mouse PXR in reporter gene assays and up-regulated xenobiotic detoxification genes in the colon mucosa, but not in the liver. Silencing of PXR by RNA interference demonstrated necessity of PXR in mediating chrysin's ability to induce xenobiotic detoxification genes and NF-kB inactivation. The repression of NF-kB transcription activity by chrysin was confirmed by in vitro PXR transduction. These findings suggest that the effect of chrysin in preventing chemically induced colitis is mediated in large part by a PXR/NF-kB pathway. The data also suggest that chrysin or chrysin-like flavonoids could be further developed as intestine-specific PXR activators.