Usnic acid (UA) is one of the well-known lichen metabolites that induces liver injury. It is mainly extracted from Usnea longissima and U. diffracta in China or from other lichens in other countries. U. longissima has been used as traditional Chinese medicine for treatment of cough, pain, indigestion, wound healing and infection. More than 20 incidences with hepatitis and liver failure have been reported by the US Food and Drug Administration since 2000. UA is an uncoupler of oxidative phosphorylation causing glutathione and ATP depletion. Previous histological studies observed extensive cell and organelle swellings accompanied with hydrotropic vacuolization of hepatocytes.
Aim of the study
This study was to investigate the mechanism of UA-induced liver toxicity in normal human L02 liver cells and ICR mice using various techniques, such as immunoblotting and siRNA transfection.
Materials and methods
Assays were performed to evaluate the oxidative stress and levels of glutathione, malondialdehyde and superoxide dismutase. Double flouresencence staining was used for the detection of apoptotic cell death. The protein expressions, such as glutathione S transferase, glutathione reductase, glutathione peroxidase 4, catalase, c-Jun N-terminal protein kinase, caspases, gastamin-D and porimin were detected by Western blotting. Comparisons between transfected and non-transfected cells were applied for the elucidation of the role of porimin in UA-induced hepatotoxicity. Histopathological examination of mice liver tissue, serum total bilirubin and hepatic enzymes of alanine aminotransferase and aspatate aminotransferase were also studied.
The protein expressions of glutathione reductase, glutathione S transferase and glutathione peroxidase-4 were increased significantly in normal human L02 liver cells. Catalase expression was diminished in dose-dependent manner. Moreover, (+)-UA did not induce the activation of caspase-3, caspase-1 or gasdermin-D. No evidence showed the occurrence of pyroptosis. However, the porimin expressions were increased significantly. In addition, (+)- UA caused no cytotoxicity in the porimin silencing L02 cells.
In conclusion, (+)-UA induces oncotic L02 cell death via increasing protein porimin and the formation of irreversible membrane pores. This may be the potential research area for future investigation in different aspects especially bioactivity and toxicology.


Dr. Sukfan Phyllis Kwong received her Bachelor Degree in Pharmacy from the University of Wisconsin-Madison, USA in 1993. She gained her Master of Clinical Pharmacy from the University of Sunderland in 2007. She practiced in both community and hospital pharmacy over 20 years. In 2020, she obtained her Ph.D in traditional Chinese medicine from the Shanghai University of Traditional Chinese Medicine. Her research interests are analytical chemistry, pharmacology, toxicology and therapeutics in both chemical and natural products.