Inhibition of cytochrome P450s enhances (+)-usnic acid cytotoxicity in primary cultured rat hepatocytes
Article first published online: 20 MAY 2013
Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
Journal of Applied Toxicology
Volume 34, Issue 8, pages 835–840, August 2014
How to Cite
Shi, Q., Greenhaw, J. and Salminen, W. F. (2014), Inhibition of cytochrome P450s enhances (+)-usnic acid cytotoxicity in primary cultured rat hepatocytes. J. Appl. Toxicol., 34: 835–840. doi: 10.1002/jat.2892
- Issue published online: 25 JUN 2014
- Article first published online: 20 MAY 2013
- Manuscript Accepted: 5 APR 2013
- Manuscript Revised: 23 MAR 2013
- Manuscript Received: 8 MAR 2013
- usnic acid;
- cytochrome P450
(+)-Usnic acid (UA) is consumed as a dietary supplement to promote weight loss; however, dietary supplements containing UA have been associated with clinical cases of severe liver injury. UA has been shown to be hepatotoxic in rats and is extensively metabolized by hepatic cytochrome P450s (CYPs); therefore, we examined if UA metabolism results in the formation of cytotoxic metabolites or if metabolism is a detoxification process in primary rat hepatocytes. When CYP activity was suppressed by the non-isoenzyme-selective inhibitor SKF-525A (20 μM), or the CYP1A inhibitor alpha-naphthoflavone (10 μM), or the CYP3A inhibitor ketoconazole (25 μM), the cytotoxicity of UA at 3 ~ 6 μM after 3 ~ 20 h of exposure was significantly increased as measured by lactate dehydrogenase (LDH) leakage. At 2 h after UA exposure, an earlier time point prior to LDH release, these CYP inhibitors potentiated UA-induced inhibition of cellular respiration as determined by the Clark type oxygen electrode. Cellular adenosine triphosphate (ATP) depletion by UA was also exacerbated by these CYP inhibitors. The CYP2B/2C inhibitor, ticlopidine at 20 μM, showed no effects in parallel experiments. These data demonstrate that UA is bio-transformed to less toxic metabolites in rat primary hepatocytes, probably mainly by CYP1A and 3A, but not 2B/2C. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.