Potential Beneficial Role of Nitric Oxide in SARS-CoV-2 Infection: Beyond Spike-Binding Inhibition

In Vitro study showing that nitric oxide (NO) inhibits SARS-CoV-2 spike protein binding to ACE2 and reduces ACE2 enzymatic activity. Authors showed that NO donors DETA-NONOate (DETA-NO) and S-nitrosoglutathione (GSNO) significantly decreased ACE2 activity, with GSNO showing stronger inhibition comparable to the specific ACE2 inhibitor MLN-4760. The binding of both alpha and gamma variants of SARS-CoV-2 spike protein was reduced by NO donors in HepG2 cells and ACE2-transfected A549 lung epithelial cells, without affecting cell viability. Using a co-culture system with murine peritoneal macrophages stimulated to produce NO, authors confirmed that endogenous NO production also inhibited spike protein binding to ACE2. The study utilized multiple experimental approaches to validate NO's effects: recombinant protein assays for ACE2 activity, flow cytometry for spike binding, and immunofluorescence for ACE2 expression. NO's dual action of inhibiting both ACE2 activity and spike protein binding suggests potential therapeutic applications for COVID-19.