gms | German Medical Science

Objective: The cancer-preventive and anti-proliferative effects of the green tea main constituent epigallocatechin gallate (EGCG) are widely supported by epidemiological, cell culture, animal and clinical studies. They are the result of its anti-oxidative effect, regulation of the cell cycle, inhibition of cell proliferation and induction of apoptosis in tumor cells. In prior experiments we showed a concentration and time-dependent decrease in viability of primary glioblastoma cell cultures under the influence of EGCG.

Method: To determine some effects EGCG exerts on glioblastoma cells, a primary cell culture was incubated with EGCG in concentrations of 100nM (physiological) and 500μM (IC50, previously determined) as well as with a commercially available green tea extract (same concentrations) over twelve hours. Apoptosis and autophagy were determined via Western Blot analysis of Caspase-3 and PARP cleavage, LC3B conversion and ubiquitination. To prove the anti-oxidative properties of EGCG, its scavenging effect was analysed by detection of reactive oxygen (ROS, DCFDA) and nitrogen (NO, Griess reagent) species.

Results: After six hours of treatment with EGCG, a dose-dependent activation of Protein Kinase B (pAKT, 2.4 fold) and NFκB (p50, 2.9 fold) was detected. This hints at a possible activation of prosurvival signaling pathways, which decreased after another six hours of treatment (pAKT 0.6 fold; NFκB p50 2.1 fold).

In all IC50 concentration-treated cells after twelve hours of incubation, we revealed strong Caspase-3 cleavage (4.8 fold) and PARP cleavage (2.1 fold), typical for apoptosis. We could also detect LC3B conversion (2.1 fold) and protein ubiquitination (3.6 fold), which are predictors for autophagy.

In the cultured cells, the induced ROS production was reduced (12%). As qPCR revealed, inducible NO synthase (iNOS) was up-regulated (4.8 fold), so the induced production of reactive NO was completely reversed.

Conclusions: Our data show that in a physiological concentration EGCG has both a growth-promoting as well as an anti-oxidative effect on glioblastoma cells. In a concentration of 500μM the substance dramatically inhibits cell growth via apoptotic and autophagic pathways. According to our data, drinking green tea or taking green tea concentrate as nutritional supplement can be cancer-preventive even for intracranial tumors. It is also possible, that EGCG taken in high doses has the ability to inhibit the proliferation of already existing tumor cells in vivo.