Thymol, a monoterpene phenolic derivative of cymene, abrogates mercury-induced oxidative stress resultant cytotoxicity and genotoxicity in hepatocarcinoma cells

Thymol (TOH) was investigated for its ability to protect against mercuric chloride (HgCl2)-induced cytotoxicity and genotoxicity using human hepatocarcinoma (HepG2) cell line. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay confirmed the efficacy of TOH pretreatment in attenuating HgCl2-induced cytotoxicity. Pretreatment with TOH inhibited HgCl2-induced genotoxicity, depolarization of mitochondrial membrane, oxidative stress, and mitochondrial superoxide levels. Interestingly, TOH (100 mu M) alone elevated the intracellular basal glutathione S-transferase (GST) levels and TOH pretreatment abrogated the decrease in glutathione, GST, superoxide dismutase, and catalase levels even after HgCl2 intoxication. Furthermore, TOH was also capable of inhibiting HgCl2-induced apoptotic as well as necrotic cell death analyzed by flowcytometric analysis of cells dual stained with Annexin-FITC/propidium iodide. The present findings clearly indicate the cytoprotective potential of TOH against HgCl2-induced toxicity, which may be attributed to its free radical scavenging ability which facilitated in reducing oxidative stress and mitochondrial damage thereby inhibiting cell death. (c) 2014 Wiley Periodicals, Inc. Environ Toxicol 30: 968-980, 2015.