Mechanism of Antiviral Activity of Nitazoxanide against the Influenza Virus: Effect of Tizoxanide on AdenosineTriphosphate in Influenza-virus Infected Madin Darby Canine Kidney Cells

Background Nitazoxanide (NTZ) is a broad-spectrum antiviral undergoing clinical development for treating influenza and other viral respiratory infections such as those caused by rhinovirus/enterovirus and coronavirus including the emerging SARS-CoV-2. Methods Nitazoxanide is a mild uncoupler of oxidative phosphorylation, which is modulating the ATP production in cells. ATP is an essential component of viral replication, and we have evaluated the effect of tizoxanide (TIZ), the active circulating metabolite of NTZ, on ATP in Madin-Darby canine kidney (MDCK) cells and in MDCK cells infected with influenza A and B viruses. Results TIZ decreased cellular ATP in a dose-dependent manner in MDCK cells and in MDCK cells infected with influenza A and B viruses. Maximum inhibition of ATP in influenza infected or uninfected MDCK cells reached up to 45% after 6 and 24 hours of exposure to 100µM TIZ. The decrease in cellular ATP did not affect cell viability and was reversible after eliminating TIZ from the culture. Conclusion The concentrations of TIZ required to decrease cellular ATP levels were similar to those reported to inhibit replication of influenza A and B viruses in our laboratory. A decrease in ATP triggers activation of AMP-activated protein kinase, which is known to suppress the secretion of pro-inflammatory cytokines. Additional studies are warranted to evaluate the effect of TIZ on mitochondrial function.