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Green tea & genotoxicity

Associates at the Ruder Boskovic Institute, Zagreb, Croatia have been investigating the genotoxic effects of compounds within green tea (Camellia sinensis).

Green tea is a rich source of flavonoids, which are secondary plant metabolites.  Flavonoids tend to have a similar chemical structure. They are characterised by condensed aromatic rings, which give specific colour, taste and smell, and are involved in defence against predators and microorganisms, and can also act as repellents.

A wide range of compounds naturally present in food can have beneficial or detrimental effects on human DNA.   For example, they may scavenge free radicals, inhibit mutagen uptake or mutagenic biotransformation, activate or modulate cellular detoxifying mechanisms, and protect DNA from nucleophilic attack.  Flavonoids scavenge free radicals, which can be detrimental to DNA, and flavonoids can also decrease or increase the activity of enzymes and cell receptors. 

Previously, green tea has been shown to contain several bioactive compounds which protect the cell and prevent tumour development. In this study, the researchers evaluated the potential cytotoxic and pro-oxidative effects of green tea extract and its two main flavonoid constituents; epigallocatechin gallate (EGCG) and epicatechin gallate (ECG), on human laryngeal carcinoma cell line (HEp2) and its cross-resistant cell line (CK2).

The aim of this investigation was to see if the green tea extract and its two flavonoids could increase the sensitivity of the cisplatin-resistant cell line CK2 in comparison to the parental cell line (HEp2).

The alkaline comet assay method was used together with an image analysis system (supplied by Perceptive Instruments).  To measure DNA damage, the researchers selected per cent tail DNA (% tail DNA) as the parameter to report. A total of 150 comets per sample (50 from each replicate slide) were scored and the data was pooled.  (For more information on data presentation and the combining of data sets, please read our Comet Assay IV data reporting page.)

A 48 hour incubation of HEp2 cells with green tea extract did not induce significant primary DNA damage in comparison to the negative control, but the 72 hour incubation did.  In contrast, 48 hour incubation of HEp2 cells with ECG or EGCG alone decreased % tail DNA in comparison to negative control, but % tail DNA after 72 hours incubation was similar to the negative control.

The cross-resistant sub-line CK2 showed no significant changes in % tail DNA whether exposed to green tea extract or either of the flavonoids and regardless of incubation time.

The results of this investigation, using the comet assay, showed that green tea extract caused DNA damage. Its genotoxic effect increased with the time of exposure.  DNA damage was more pronounced in the parental HEp2 cell line than in the resistant CK2 subline. The researchers suppose that the HEp2 cell line has a more susceptible genome and it is also possible that the CK2 cell line developed more effective endogenous repair mechanisms.

It is noteworthy to mention that the pro-oxidant effect of green tea was determined at concentrations higher than those found in traditionally prepared green tea infusions.

Happy tea drinking!

This case study is based upon:
Genotoxic effects of green tea extract on human laryngeal carcinoma cells in vitro.
Durgo K, Kostić S, Gradiški K, Komes D, Osmak M, Franekić J.
Arh Hig Rada Toksikol 2011;62:139-146