Laggera pterodonta (DC.) Benth. is a traditional Chinese medicine. The previous study revealed that the crude extracts of this herb could inhibit influenza virus infection, but its anti-influenza components and underlying mechanism of action remain unknown. Column chromatography was performed to isolate components from the plant. Activity against influenza virus of the compound was determined by CPE inhibition assay. Neuraminidase (NA) inhibition was measured by chemiluminescence assay. The anti-virus and anti-inflammation effects were determined using dual-luciferase reporter assay, immunofluorescence, quantitative real-time PCR and luminex assay. Pterodontic acid was isolated from L. pterodonta, which showed selective anti-viral activities to H1 subtype of human influenza A virus. Meanwhile, the NA activity was not obviously inhibited by the compound. Further experiments exhibited that the compound can suppress the activation of NF-κB signal pathway and export of viral RNP complexes from the nucleus. In addition, it can significantly attenuate expression of the pro-inflammatory molecules IL-6, MIP-1β, MCP-1, and IP-10 induced by human influenza A virus (H1N1) and similarly downregulate expression of cytokines and chemokines induced by avian influenza A virus (H9N2). This study showed that in vitro antiviral activity of pterodontic acid is most probably associated with inhibiting the replication of influenza A virus by blocking nuclear export of viral RNP complexes, and attenuating the inflammatory response by inhibiting activation of the NF-κB pathway. Pterodontic acid might be a potential antiviral agent against influenza A virus.

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.

Pyrogallol, a natural polyphenol compound (1,2,3‐trihydroxybenzene), has shown efficacy in the therapeutic treatment of disorders associated with inflammation. Nevertheless, the mechanisms underlying the protective properties of pyrogallol against influenza A virus infection are not yet established. We established in this study that pyrogallol effectively alleviated H1N1 influenza A virus‐induced lung injury and reduced mortality. Treatment with pyrogallol was found to promote the expression and nuclear translocation of nuclear factor erythroid‐2‐related factor 2 (Nrf2) and peroxisome proliferator‐activated receptor gamma (PPAR‐γ). Notably, the activation of Nrf2 by pyrogallol was involved in elevating the expression of PPAR‐γ, both of which act synergistically to enhance heme oxygenase‐1 (HO‐1) synthesis. Blocking HO‐1 by zinc protoporphyrin (ZnPP) reduced the suppressive impact of pyrogallol on H1N1 virus‐mediated aberrant retinoic acid‐inducible gene‐I‐nuclear factor kappa B (RIG‐I–NF‐κB) signaling, which thus abolished the dampening effects of pyrogallol on excessive proinflammatory mediators and cell death (including apoptosis, necrosis, and ferroptosis). Furthermore, the HO‐1‐independent inactivation of janus kinase 1/signal transducers and activators of transcription (JAK1/STATs) and the HO‐1‐dependent RIG‐I‐augmented STAT1/2 activation were both abrogated by pyrogallol, resulting in suppression of the enhanced transcriptional activity of interferon‐stimulated gene factor 3 (ISGF3) complexes, thus prominently inhibiting the amplification of the H1N1 virus‐induced proinflammatory reaction and apoptosis in interferon‐beta (IFN‐β)‐sensitized cells. The study provides evidence that pyrogallol alleviates excessive proinflammatory responses and abnormal cell death via HO‐1 induction, suggesting it could be a potential agent for treating influenza.

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: Rosmarinic acid (RosA) is a natural phenolic compound that possesses a wide-range of pharmacological properties. However, the effects of RosA on influenza A virus-mediated acute lung injury remain unknown. In this study, we aimed to explore whether RosA could protect against H1N1 virus-mediated lung injury and elucidate the underlying mechanisms. Methods: Mice were intragastrically administered with RosA for 2 days before intranasal inoculation of the H1N1 virus (5LD₅₀) for the establishment of an acute lung injury model. At day 7 post-infection (p.i.), gross anatomic lung pathology, lung histopathologic, and lung index (lung weight/body weight) were examined. Luminex assay, multiple immunofluorescence and flow cytometry were performed to detect the levels of pro-inflammatory cytokines and apoptosis, respectively. Western blotting and plasmid transfection with hematopoietic-type PGD₂ synthase (h-PGDS) overexpression were conducted to elucidate the mechanisms. Results: RosA effectively attenuated H1N1 virus-triggered deterioration of gross anatomical morphology, worsened lung histopathology, and elevated lung index. Excessive pro-inflammatory reactions, aberrant alveolar epithelial cell apoptosis, and cytotoxic CD8⁺ T lung recruitment in the lung tissues induced by H1N1 virus infection were observed to be reduced by RosA treatment. In vitro experiments demonstrated that RosA treatment dose-dependently suppressed the increased levels of pro-inflammatory mediators and apoptosis through inhibition of nuclear factor kappa B (NF-κB) and P38 MAPK signaling pathways in H1N1 virus-infected A549 cells, which was accompanied by promoting activation of the h-PGDS-PGD₂-HO-1 signal axis. Furthermore, we strikingly found that h-PGDS inhibition significantly abrogated the inhibitory effects of RosA on H1N1 virus-mediated activation of NF-κB and P38 MAPK signaling pathways, resulting in diminishing the suppressive effects on the increased levels of pro-inflammatory cytokines and chemokines as well as apoptosis. Finally, suppressing h-PGDS prominently abolished the protective effects of RosA on H1N1 virus-mediated severe pneumonia and lung injury. Conclusions: Taken together, our study demonstrates that RosA is a promising compound to alleviate H1N1 virus-induced severe lung injury through prompting the h-PGDS-PGD₂-HO-1 signal axis.

Eucommia ulmoides Oliver (Du-Zhong) is an ancient Chinese herbal remedy used for the treatment of various diseases. To date, the effects of its constituent lignans on influenza viruses remain to be elucidated. In the present study, a lignan glycoside was isolated and purified from Eucommia ulmoides Oliver. Its structures were identified via extensive spectroscopic analysis, and its antiviral and anti-inflammatory activities, specifically against influenza viruses, were determined via a cytopathic effect (CPE) assay, plaque-reduction assays, a progeny virus yield reduction assay, reverse transcription-quantitative polymerase chain reaction analysis and a Luminex assay. Additionally, western blot analysis was performed to investigate the underlying mechanisms of its effects against influenza viruses. The chemical and spectroscopic methods determined the structure of lignan glycoside to be (+)-pinoresinol-O--D-glucopyranoside. The CPE assay showed that (+)-pinoresinol-O--D-glucopyranoside exerted inhibitory activities with 50% inhibition concentration values of 408.81 +/- 5.24 and 176.24 +/- 4.41 mu g/ml against the influenza A/PR/8/34 (H1N1) and A/Guangzhou/GIRD07/09 (H1N1) strains, respectively. Its antiviral properties were confirmed by plaque reduction and progeny virus yield reduction assays. Additional mechanistic analyses indicated that the anti-H1N1 virus-induced effects of (+)-pinoresinol-O--D-glucopyranoside were likely due to inactivation of the nuclear factor-B, p38 mitogen-activated protein kinase and AKT signaling pathways. Furthermore, (+)-pinoresinol-O--D-glucopyranoside exhibited pronounced inhibitory effects on the expression of influenza H1N1 virus-induced pro-inflammatory mediators, including tumor necrosis factor-, interleukin (IL)-6, IL-8 and monocyte chemoattractant protein 1. The data obtained suggest that (+)-pinoresinol-O--D-glucopyranoside may be a candidate drug for treating influenza H1N1 virus infection.