Plant polyphenols and oxidative metabolites of the herbal alkenylbenzene methyleugenol suppress histone deacetylase activity in human colon carcinoma cells.

Evidence has been provided that diet and environmental factors directly influence epigenetic mechanisms associated with cancer development in humans. The inhibition of histone deacetylase (HDAC) activity and the disruption of the HDAC complex have been recognized as a potent strategy for cancer therapy and chemoprevention. In the present study, we investigated whether selected plant constituents affect HDAC activity or HDAC1 protein status in the human colon carcinoma cell line HT29. The polyphenols (-)-epigallocatechin-3-gallate (EGCG) and genistein (GEN) as well as two oxidative methyleugenol (ME) metabolites were shown to inhibit HDAC activity in intact HT29 cells. Concomitantly, a significant decrease of the HDAC1 protein level was observed after incubation with EGCG and GEN, whereas the investigated ME metabolites did not affect HDAC1 protein status. In conclusion, dietary compounds were found to possess promising HDAC-inhibitory properties, contributing to epigenetic alterations in colon tumor cells, which should be taken into account in further risk/benefit assessments of polyphenols and alkenylbenzenes.

Genotoxic potential of methyleugenol and selected methyleugenol metabolites in cultured Chinese hamster V79 cells.

Methyleugenol is a substituted alkenylbenzene classified by the European Union's Scientific Committee on Food as a genotoxic carcinogen. We addressed cytotoxicity, genotoxicity and mutagenicity caused by methyleugenol and selected oxidative methyleugenol metabolites in Chinese hamster lung fibroblasts V79 cells. Cytotoxicity was measured by two cell proliferation assays, water soluble tetrazolium salt (WST) 1 and sulforhodamine B (SRB) assays. Genotoxicity was determined by using single cell gel electrophoreses (comet assay) and the in vitro micronuclei test, while mutagenicity was investigated with the hypoxanthinephosphoribosyl transferase (hprt) assay. Methyleugenol and 1'-hydroxymethyleugenol showed no or marginal cytotoxic effects, but caused DNA strand breaks at concentrations ≥10 µM. The metabolites methyleugenol-2',3'-epoxide and 3'-oxomethylisoeugenol exhibited growth inhibitory properties with IC(50)-values of 70-90 µM after 48 h or 72 h of incubation. These metabolites significantly enhanced cytotoxicity and DNA damage after 1 h of incubation. Overall, no increase in formamidopyrimidine DNA glycosylase sensitive sites were detected with the comet assay. The metabolites 1'-hydroxymethyleugenol and methyleugenol-2',3'-epoxide exceeded the DNA strand breaking properties of the parent compound methyleugenol. However, only 3'-oxomethylisoeugenol and methyleugenol-2',3'-epoxide induced the formation of micronucleated cells in comparison to the negative control. These compounds were found to be not or rather weakly mutagenic at the hprt locus. In summary, phase I metabolites exceeded the cytotoxic and genotoxic properties of the parent compound methyleugenol.