Therapeutic Efficacy of the Supersulfide Donor NAC-S2 in Influenza Virus Pneumonia via Suppression of Excessive Inflammatory Responses.

Influenza pneumonia is characterized by excessive inflammatory responses that contribute to severe lung injury and mortality. Supersulfides, endogenously produced cysteine-derived persulfides and polysulfides, exert potent antioxidant, anti-ferroptotic, and anti-inflammatory activities; however, their therapeutic potential after disease onset remains unclear. Here, we investigated the efficacy of N-acetylcysteine tetrasulfide (NAC-S2), a highly water-soluble and cell-permeable supersulfide donor, in a mouse model of influenza A virus (IAV)-induced pneumonia. Subcutaneous administration of NAC-S2 rapidly elevated systemic levels of cysteine- and glutathione-derived supersulfides. In therapeutic treatment starting 2 days post-infection, when body weight loss and clinical signs had already developed, NAC-S2 significantly improved survival and mitigated body weight loss compared with vehicle and oxidized NAC controls. Metabolomic analysis revealed that influenza virus infection depleted lung glutathione persulfide (GSSH), while NAC-S2 effectively restored tissue GSSH levels. NAC-S2 treatment markedly reduced pulmonary interleukin (IL)-1β and IL-6 production without affecting viral load or Type-I interferon responses. Furthermore, NAC-S2 suppressed NLRP3 inflammasome activation and gasdermin D expression, leading to decreased infiltration of CD3+ T cells and myeloperoxidase-positive neutrophils. Histopathological analyses confirmed that NAC-S2 ameliorated epithelial injury, interstitial edema, and hemorrhage in infected lungs. Collectively, our findings demonstrate that NAC-S2 exerts therapeutic benefit even after the onset of severe influenza pneumonia, primarily by replenishing supersulfides and alleviating excessive inflammatory responses. Supersulfide donors represent a promising class of adjunctive therapeutics for severe viral pneumonia.