N-Acetylcysteine: An Old Drug With Variable Anti-Influenza Properties

N-acetylcysteine (NAC) is a mucolytic drug commonly used as an adjuvant therapy in patients with respiratory conditions associated with excessive mucus production. NAC also has antioxidant activities which proved useful in the management of oxidative stress. These antioxidant capacities of NAC are mostly indirect, via a pro-glutathione effect where NAC provides L-cysteine residues required for glutathione synthesis. This activity is thought to be the basis of the protective effect of NAC administration in influenza patients and in mouse models of the disease. NAC was shown to limit lung inflammation, damage associated with the virus, and limit viral growth, at least in vitro. However, the antiviral activity was highly variable depending on the influenza A strain. The reasons for these inter-strain variations are still unknown but might be related to the level of NF-κB activation required for the virus to achieve its infectious cycle.