Combination of andrographolide and baicalin inhibited influenza A virus infection through suppressing RORγt-IL-17A...

Influenza A virus (IAV), a highly contagious respiratory pathogen, has been posing a serious threat to global public health. Traditional Chinese medicines (TCM) have been demonstrated to be effective to combat viral infection in clinical by inhibiting both virus and host inflammation. Emerging evidence has suggested the synergistic role of drug combination in treating disease. Therefore, identifying a TCM combination with defined molecular mechanism is crucial for developing effective strategies against IAV infection.

Both andrographolide and baicalin have been demonstrated to exert antiviral and anti-inflammatory properties. In this study, the synergistic antiviral efficacy of the combination of andrographolide and baicalin and the underlying molecular mechanism were elucidated, alongside the optimal combination ratio for maximal therapeutic effect against IAV infections.

The mouse model of IAV infection was established via intranasal inoculation and the antiviral effects of the combined application of andrographolide and baicalin were evaluated. The chemical composition of andrographolide and baicalin was confirmed by UPLC-MS/MS analysis. The differentially expressed inflammatory cytokines and chemokines were identified using the Olink inflammation panel analysis. The role of RORγt-IL-17A axis was validated by both SR0987 (RORγt agonist) treatment in vivo and Il-17a-knockout mouse models.

The combination of andrographolide and baicalin significantly enhanced the survival, promoted weight recovery, and reduced lung injury in IAV-infected mice. The protective effect of the combination was revealed to be mediated through suppression of RORγt-IL-17A pathway. CD4⁺/IL-17A⁺ T cells and IL-17A⁺/RORγt⁺ populations, along with the proinflammatory cytokines, were reduced by the combined andrographolide and baicalin treatment upon infection. The critical role of RORγt-IL-17A upon IAV infection was further confirmed in vivo.

The 1:1.5 ratio of andrographolide and baicalin in the combination displayed the strongest anti- IAV activity. Mechanistically, the synergistic effect was mediated by their suppression of the retinoid orphan receptor gamma t (RORγt)-interleukin 17A (IL-17A) pathway, which significantly ameliorated the excessive pulmonary inflammatory responses upon IAV infection.