Gaseous nitric oxide reduces influenza infectivity in vitro

Gaseous nitric oxide (gNO) is an approved vasodilator drug for inhalation up to a maximum dose of 80 ppm. While gNO has been shown, in vitro, to be an effective antibacterial agent (at 160 ppm), NO-donor compounds have been shown to inhibit a variety of viruses at varying stages of replication. This research was done in order to determine whether gNO at 80 or 160 ppm possesses an antiviral effect on influenza viruses. Three strains of influenza (A and B) were exposed to gNO for up to 180 min, before and after infection of MDCK cells. In search for possible mechanism of antiviral action, Neuraminidase (NA) inhibition assay of H1N1 that was exposed to gNO was performed. Results show that when virions were exposed to gNO prior to infection a complete inhibition of infectivity was achieved for all three strains. Post infection exposure of influenza with gNO resulted in about 30% inhibition of infectivity. Further testing showed that when eliminating the pH effect by exposing a dried virus to gNO, 90% inhibition was found after 2h exposure. NA activity, of whole dried H1N1 virus, was found to be inhibited by gNO (80%). These results suggest that 80 and 160 ppm gNO have a time dependent antiviral effect on influenza strains of viruses during various stages of cellular infection, which are not due to concomitant changes in pH in the surrounding milieu. Viral NA inhibition by gNO was shown and may be responsible for this antiviral effect.