Unveiling the antiviral activity of Adiantum capillus-veneris L. against influenza A(H1N1)

The influenza virus poses a global health threat, with current management involving antiviral drugs and annual vaccination, although challenges of resistance exist. Herbal medicine, particularly Adiantum capillus-veneris L., traditionally used for respiratory diseases, shows anti-inflammatory and antioxidant properties. The potential anti-influenza effect of A . capillus-veneris plant extract remains underexplored. This research assesses the aqueous-alcoholic extract of A . capillus-veneris against influenza A (H1N1) virus in vitro, aiming to explore alternative containment methods for the virus. The 50% cytotoxic concentration (CC50) of A. capillus-veneris aqueous-alcoholic extract in MDCK cell culture was determined using the MTT assay. Extracts at varying concentrations were introduced in three stages: before, during, and after viral inoculation. Oseltamivir was added separately one hour post-viral inoculation. Synergistic effects of the extract in combination with oseltamivir were tested. Cytopathic effects (CPE) were observed 48–72 h post-inoculation, and virus titers were determined using hemagglutination assay (HA), real-time PCR, and TCID50 assays. The A. capillus-veneris extract showed a CC50 of ~ 1 mg/mL (MTT assay), indicating moderate cytotoxicity. TCID50 results revealed strong antiviral activity against influenza A(H1N1) virus: concentrations of 0.02–0.5 mg/mL significantly reduced viral titers. At 0.1 mg/mL, pre-treatment reduced viral load by 99.9%, and 0.5 mg/mL suppressed viral replication when applied during infection. Combining oseltamivir at concentrations of 0.5 and 0.05 mg/mL with extract at 0.5, 0.1, and 0.05 mg/mL concentrations yielded a synergistic effect against the influenza A(H1N1) virus, surpassing the efficacy observed with oseltamivir alone. These findings suggest that A. capillus-veneris extract possesses potent anti-influenza activity against influenza A(H1N1). Moreover, it enhances antiviral efficacy when combined with oseltamivir. Future research should focus on identifying the specific active components of the extract and determining the precise stage at which it inhibits viral replication.