Inhibition by caffeic acid of the influenza A virus multiplication in vitro

Caffeic acid has been shown to inhibit the multiplication of influenza A virus in vitro, whereas caffeine, quinic acid and chlorogenic acid do not. Caffeic acid has also been shown to have antiviral activity against herpes simplex virus (DNA virus) and polio virus (RNA virus). In the present study, a comparison of the one-step growth curve of the influenza virus in the presence of caffeic acid with that in the absence of the reagent showed that an eclipse period of the virus multiplication in the infected cells was not affected by the reagent, while the progeny virus yield was markedly decreased in the presence of caffeic acid. In additional experiments, it was found that the addition of caffeic acid at an early time point post-infection (within 3 h post-infection) was mandatory for extensive antiviral activity, suggesting that a major target of the reagent exists in the early stages of infection. Simultaneously with the decrease in the progeny virus yield, both the virus-induced cytopathic effects and apoptotic nuclear fragmentation were markedly suppressed by the reagent, suggesting that caffeic acid suppresses, at least temporally, the degeneration of the virus-infected cells and that the observed antiviral activity is likely not the secondary result of the cytotoxic effects of the reagent. These results suggest the potential pharmacological use of caffeic acid or its derivatives as an antiviral drug against influenza A virus.