Comparative study of genotoxic, antigenotoxic and cytotoxic activities of monoterpenes camphor, eucalyptol and thujone in bacteria and mammalian cells.

Genotoxic/antigenotoxic, mutagenic/antimutagenic and cytotoxic effects of monoterpenes camphor, eucalyptol and thujone were determined in bacteria and mammalian cells using alkaline comet assay, Escherichia coli K12 reversion test and MTT assay, respectively. When applied in low doses (up to 200 μM in bacterial assay and 50 μM in comet assay) monoterpenes protected repair proficient E. coli and Vero cells against UV-induced mutagenesis and 4NQO-induced DNA strand breaks, respectively. Antimutagenic response was not detected in nucleotide excision repair (NER) deficient bacteria. When monoterpenes were applied in higher doses, a weak mutagenic effect was found in mismatch repair (MMR) and NER deficient E. coli strains, while induction of DNA strand breaks was evident in human fetal lung fibroblasts MRC-5, colorectal carcinoma HT-29 and HCT 116 cells, as well as in Vero cells. Moreover, the involvement of NER, MMR and RecBCD pathways in repair of DNA lesions induced by monoterpenes was demonstrated in E. coli. Camphor, eucalyptol and thujone were cytotoxic to MRC-5, HT-29 and HCT 116 cells. The most susceptible cell line was HCT 116, with IC50 values of 4.5 mM for camphor, 4 mM for eucalyptol and 1 mM for thujone. Observed effects of monoterpenes are consistent with hormesis response, characterized by a low dose beneficial effect and a high dose adverse effect of a stressor agent, and provide a basis for further study of both chemopreventive and chemotherapeutic potential of camphor, eucalyptol and thujone.