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The effect of xantohumol on normal and cancer cell<br />
lines and its modulatory effects on genotoxicity of<br />
heterocyclic amine (IQ) in HepG2 cells<br />
Irena Zajc, Janja Plazar, Metka Filipi~ and Tamara Lah<br />
Department of Genetic Toxicology and Cancer Biology, National Institute<br />
of Biology; Ve~na pot 111, 1000 Ljubljana, Slovenia, www.nib.si<br />
Xanthohumol (XN) is the principal prenylated chalcone of the female inflorescences<br />
of the hop (Humulus lupulus L.) and commonly used as a preservative and<br />
flavouring agent in beer. It’s natural role is to protect the plants against insect<br />
feeding. XN has been reported to have a broad spectrum of inhibitory mechanisms<br />
at the initiation, promotion and progression stages of carcinogenesis. The aims<br />
of the present study were to explore: 1) the cytotoxicity of XN on normal and<br />
neoplastic human cell lines and its effects on cell adhesion and apoptosis and<br />
2) the potential of XN to inhibit the heterocyclic amine IQ induced genotoxicity in<br />
S. typhimurium TA98 and in human hepatoma HepG2 cells.<br />
Normal human umbilical vein cells (HUVEC) and diploid immortalized human breast<br />
epithelial cell line (MCF10A) with normal karyotype, and two tumour cell lines (breast<br />
MCF10AneoT and glioblastoma U87 cell line) were used to study cytotoxicity of XN<br />
and its effect on adhesion of the two cancer cell lines by MTT assay. The effect of<br />
XN on apoptosis was studied by staining the cells with DNA binding dyes acridine<br />
orange and ethidium bromide. Mutagenicity and antimutagenicity of XN was tested<br />
with S. typhimurium TA98 using the standard plate incorporation procedure (Ames<br />
test). Genotoxicity of XN and its potential to inhibit IQ induced DNA damage in<br />
human hepatoma HepG2 cells were determined by the comet and the potential of<br />
XN to modulate CYP1A activity was determined with the EROD assays.<br />
XN was cytotoxic for cancer cells (U87 and MCF10AneoT) at 15 µM concentration<br />
and for the normal cells (HUVEC and MCF10A) at 50 µM concentration.<br />
At subtoxic concentrations, XN had a significant impact on adhesion of U87 cell<br />
line to Matrigel and fibronectin, but it did not affect the adhesion of MCF10AneoT.<br />
At 30 µM concentration, XN triggered apoptosis in all four cell lines. The proportion of<br />
apoptotic cells did not differ among cell lines after 24 hours, whereas after 48 hours,<br />
it was significantly higher in cancer cell lines than in the normal cells. In the Ames<br />
test with Salmonella typhimurium TA98, XN showed dose dependent antimutagenic<br />
activity against the indirect acting mutagen IQ. In HepG2 cells, XN reduced EROD<br />
activity and at 10 µg/ml (28.25 µM) concentration completely prevented IQ induced<br />
DNA damage, indicating that the mechanism of XN antigenotoxicity is inhibition of<br />
metabolic activation of IQ.<br />
In conclusion, this data showed selective cytotoxicity of XN for cancer cells, which<br />
can at least partly contribute to selective induction of apoptosis. Furthermore, XN<br />
is a potent inhibitor of IQ induced genotoxicity. Therefore, XN has a potential as<br />
chemopreventive agent at the initiation and progression step of cancer development<br />
and could present a candidate for prevention and treatment of cancer.<br />
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