In vitro antiviral activity of hypothiocyanite against A/H1N1/2009 pandemic influenza virus

Influenza virus spreads via small particle aerosols, droplets and fomites, and since it can survive for a short time on surfaces, can be introduced into the nasal mucosa before it loses infectivity. The hypothiocyanite ion (OSCN−), product of the lactoperoxidase/H2O2/SCN− system of central airways, is emerging as an important molecule for innate defense mechanism against bacteria, fungi and viruses. Here we demonstrated that OSCN− displays virucidal activity in vitro against the A/H1N1 2009 pandemic influenza virus. The concentration required to inhibit viral replication by 50% was 2 μM when virus were challenged directly with OSCN− before cell inoculation. These values were even lower when inoculated cells were maintained in contact with enzyme free-OSCN− in the culture medium. The last experimental conditions better reflect those of tracheobronchial mucosa, where HOSCN/OSCN− is retained in the air–liquid interface and inactivates both the viruses approaching the epithelium from outside and those released from the inoculated cells after the replication cycle. Importantly no OSCN− cytotoxicity was observed in the cellular system employed. The lack of toxicity in humans and the absence of damage on surfaces of fomites suggest a potential use of OSCN− to avoid mucosal and environmental transmission of influenza virus. Since hypothiocyanite is normally present in human airways a low risk of viral resistance is envisaged. In vivo confirmatory studies are needed to evaluate the appropriate dose, regimen and formulation.