Genotoxicity of (+)- and (-)-usnic acid in mice.

Usnic acid, which is the most widespread and well-studied secondary lichen compound, has antibacterial and cytotoxic effects. Usnic acid is present in lichens as the (+)- and (-)-enantiomers, which have different biological activities. We used a DNA-comet assay to determine the genotoxic effect of (+)- and (-)-usnic acid in the liver and kidney cells of mice. The genotoxic effect of usnic acid was only observed 1 h after oral administration. Usnic acid doses of 100 and 50 mg/kg resulted in DNA damage in the liver and kidney cells. The genotoxic effect of usnic acid is associated with oxidative stress in cells. There were no significant differences in the effects of (+)- and (-)-enantiomers.