Background H9N2 avian influenza viruses (AIVs) infect avian and mammalian hosts and provide internal genes for new emerging highly pathogenic avian viruses that cause severe pneumonia with high mortality, for which few medications are available. Arctiin, a bioactive lignan glycoside, has been reported to possess multiple pharmacological properties. However, the effect of arctiin on H9N2 virus infection is unclear. In the current study, we analyzed the effect of arctiin on H9N2 virus infection and the underlying molecular mechanism in vitro. Methods The antiviral effect against H9N2 virus was determined by plaque reduction assay (PRA) and progeny virus reduction assay. We employed MTT assay, qRT-PCR, ELISA, immunofluorescence and Western blotting to better understand the anti-inflammatory effect and corresponding mechanism of arctiin on H9N2 virus-infected cells. Results The results showed that arctiin had antiviral activity against H9N2 virus. Arctiin treatment reduced H9N2 virus-triggered proinflammatory cytokines, such as IL-6, and TNF-α. Moreover, arctiin significantly suppressed H9N2 virus-mediated expression of COX-2 and PGE2. Furthermore, we found that arctiin inhibited H9N2 virus-mediated activation of RIG-I/JNK MAPK signaling. Interestingly, arctiin treatment obviously reversed H9N2 virus-induced reduction of Nrf2, increased the nuclear translocation of Nrf2, and upregulated Nrf2 signaling target genes (HO-1 and SOD2). Zinc protoporphyrin (Znpp)—an HO-1 inhibitor—weakened the inhibitory effect of arctiin on H9N2 virus-induced RIG-I/JNK MAPK and proinflammatory mediators. Conclusion Taken together, these results suggested that the anti-inflammatory effects of arctiin on H9N2 virus infection may be due to the activation of Nrf2/HO-1 and blocked RIG-I/JNK MAPK signaling; thus, arctiin may be a promising agent for prevention and treatment of H9N2 virus infections.

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Influenza-related acute lung injury (ALI) is a life-threatening condition that results mostly from uncontrolled replication of influenza virus (IV) and severe proinflammatory responses. The methoxy flavonoid compound 5-methoxyflavone (5-MF) is believed to have superior biological activity in the treatment of cancer. However, the effects and underlying mechanism of 5-MF on IV-mediated ALI are still unclear. Here, we showed that 5-MF significantly improved the survival of mice with lethal IV infection and ameliorated IV-mediated lung edema, lung histological changes, and inflammatory cell lung recruitment. We found that 5-MF has antiviral activity against influenza A virus (IAV), which was probably associated with increased expression of radical S-adenosyl methionine domain containing 2 (RSAD2) and suppression of endosomal acidification. Moreover, IV-infected A549 cells with 5-MF treatment markedly reduced proinflammatory mediator expression (IL-6, CXCL8, TNF-α, CXCL10, CCL2, CCL3, CCL4, GM-CSF, COX-2, and PGE2) and prevented P-IKBα, P-P65, and P-P38 activation. Interestingly, we demonstrated that 5-MF treatment could trigger activation of AMP-activated protein kinase (AMPK)α in IV-infected A549 cells, as evidenced by activation of the AMPKα downstream molecule P53. Importantly, the addition of AMPKα blocker compound C dramatically abolished 5-MF-mediated increased levels of RSAD2, the inhibitory effects on H1N1 virus-elicited endosomal acidification, and the suppression expression of proinflammatory mediators (IL-6, TNF-α, CXCL10, COX-2 and PGE2), as well as the inactivation of P-IKBα, P-P65, and P-P38 MAPK signaling pathways. Furthermore, inhibition of AMPKα abrogated the protective effects of 5-MF on H1N1 virus-mediated lung injury and excessive inflammation in vivo. Taken together, these results indicate that 5-MF alleviated IV-mediated ALI and suppressed excessive inflammatory responses through activation of AMPKα signaling.

Diosmetin suppressed the enhanced pro-inflammatory response and apoptosis via inhibition of the augmentation of NF-κB and P38 kinase activation in a PPAR-γ-dependent manner, facilitating the alleviation of B[a]P-exacerbated H1N1 virus-induced respiratory illness.

Background Acute lung injury (ALI) arises from sepsis or bacterial infection, which are life-threatening respiratory disorders that cause the leading cause of death worldwide. 5-Methoxyflavone, a methylated flavonoid, is gaining increased attention for its various health benefits. In the current study, we investigated the potential effects of 5-methoxyflavone against LPS-mediated ALI and elucidated the corresponding possible mechanism. Methods A mouse model with ALI was established by intratracheal instillation of LPS, and lung pathological changes, signaling pathway related proteins and apoptosis in lung tissues were estimated by H&E staining, immunofluorescence and TUNEL assay, respectively. Cell viability was evaluated by MTT assay; protein levels of pro-inflammatory mediators were measured by ELISA assay; levels of ROS and M1 macrophage polarization were assayed by flow cytometry; the expression of Nrf2 signaling, NOX4/TLR4 axis and P-STAT1 were detected by western blotting. Results Our results showed that 5-methoxyflavone treatment inhibited LPS-induced expression of NOX4 and TLR4 as well as the activation of downstream signaling (NF-κB and P38 MAPK), which was accompanied by markedly decreased ROS levels and pro-inflammatory cytokines (IL-6, TNF-α, MCP-1, and IL-8) in BEAS-2B cells. Moreover, we revealed that these effects of 5-methoxyflavone were related to its Nrf2 activating property, and blockade of Nrf2 prevented its inhibitory effects on NOX4/TLR4/NF-κB/P38 MAPK signaling, thus abrogating the anti-inflammatory effects of 5-methoxyflavone. Besides, the Nrf2 activating property of 5-methoxyflavone in RAW264.7 cells led to inhibition of LPS/IFN-γ-mediated STAT1 signaling, resulting in suppression of LPS/IFN-γ-induced M1 macrophage polarization and the repolarization of M2 macrophages to M1. In a mouse model of LPS-induced ALI, 5-methoxyflavone administration ameliorated LPS-mediated lung pathological changes, the increased lung index (lung/body weight ratio), and epithelial cell apoptosis. Meanwhile, we found 5-methoxyflavone effectively suppressed the hyperactive signaling pathways and the production of excessive pro-inflammatory mediators. Moreover, 5-methoxyflavone reduced LPS-mediated M1 macrophage polarization associated with elevated P-STAT1 activation in the lung tissues. In addition, 5-methoxyflavone improved the survival of LPS-challenged mice. Conclusion These results indicated that 5-methoxyflavone might be suitable for the development of a novel drug for ALI therapeutic.