Insights into the mechanism of action of pterostilbene against influenza A virus-induced acute lung injury.

BACKGROUND: Severe respiratory system illness caused by influenza A virus infection is associated with excessive inflammation and abnormal apoptosis in alveolar epithelial cells (AEC). However, there are limited therapeutic options for influenza-associated lung inflammation and apoptosis. Pterostilbene (PTE, trans-3,5-dimethoxy-4-hydroxystilbene) is a dimethylated analog of resveratrol that has been reported to limit influenza A virus infection by promoting antiviral innate immunity, but has not been studied for its protective effects on virus-associated inflammation and injury in AEC. PURPOSE: Our study aimed to investigate the protective effects and underlying mechanisms of PTE in modulating inflammation and apoptosis in AEC, as well as its effects on macrophage polarization during influenza virus infection. STUDY DESIGN AND METHODS: A murine model of influenza A virus-mediated acute lung injury was established by intranasal inoculation with 5LD50 of mouse-adapted H1N1 viruses. Hematoxylin and eosin staining, immunofluorescence, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, western blotting, Luminex and flow cytometry were performed. RESULTS: PTE effectively mitigated lung histopathological changes and injury induced by H1N1 viruses in vivo. These beneficial effects of PTE were attributed to the suppression of inflammation and apoptosis in AEC, as well as the modulation of M1 macrophage polarization. Mechanistic investigations revealed that PTE activated the phosphorylated AMP-activated protein kinase alpha (P-AMPKα)/sirtui1 (Sirt1)/PPARγ coactivator 1-alpha (PGC1α) signal axis, leading to the inhibition of nuclear factor kappa-B (NF-κB) and p38 mitogen-activated protein kinase (MAPK) signaling induced by H1N1 viruses, thereby attenuating inflammation and apoptosis in AEC. PTE also forced activation of the P-AMPKα/Sirt1/PGC1α signal axis in RAW264.7 cells, counteracting the activation of phosphorylated signal transducer and activator of transcription 1 (P-STAT1) induced by H1N1 viruses and the augment of P-STAT1 activation in RAW264.7 cells with interferon-gamma (IFN-γ) pretreatment before viral infection, thereby reducing H1N1 virus-mediated M1 macrophage polarization as well as the enhancement of macrophages into M1 phenotypes elicited by IFN-γ pretreatment. Additionally, the promotion of the transition of macrophages towards the M2 phenotype by PTE was also related to activation of the P-AMPKα/Sirt1/PGC1α signal axis. Moreover, co-culturing non-infected AEC with H1N1 virus-infected RAW264.7 cells in the presence of PTE inhibited apoptosis and tight junction disruption, which was attributed to the suppression of pro-inflammatory mediators and pro-apoptotic factors in an AMPKα-dependent manner. CONCLUSION: In conclusion, our findings suggest that PTE may serve as a promising novel therapeutic option for treating influenza-associated lung injury. Its ability to suppress inflammation and apoptosis in AEC, modulate macrophage polarization, and preserve alveolar epithelial cell integrity highlights its potential as a therapeutic agent in influenza diseases.

Rosmarinic acid treatment protects against lethal H1N1 virus-mediated inflammation and lung injury by promoting activation of the h-PGDS-PGD2-HO-1 signal axis.

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.

Arctiin suppresses H9N2 avian influenza virus-mediated inflammation via activation of Nrf2/HO-1 signaling.

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.