Usnic acid reactive metabolites formation in human, rat, and mice microsomes. Implication for hepatotoxicity

Usnic acid is a lichen compound which is extensively studied due to its cytotoxic, antiproliferative, antimicrobial, antiviral, antiprotozoal, and anti-inflammatory activities. Despite a broad spectrum of biological properties, usnic acid is a hepatotoxic agent, thus its potential use as a drug is limited. Certain hepatotoxic drugs may act by generating reactive metabolites that damage the liver. The aim of the study was to predict the biotransformation of usnic acid enantiomers to reactive products using a trapping assay with glutathione in human, rat, and mice liver microsomes. Our results indicate that each enantiomer forms two reactive metabolites; in turn, these metabolites form adducts with glutathione, which may partially explain the toxicity of usnic acid. In silico analysis indicated structural alerts for the generation of reactive metabolites in usnic acid formula. This study proposes a novel mode of the hepatic toxicity of usnic acid enantiomers; it also provides some useful suggestions for designing safer usnic acid derivatives.