Induction of apoptosis and inhibition of telomerase activity by aqueous extract from Platycodon grandiflorum in human lung carcinoma cells

The objective of the present study was to investigate the effect of aqueous extract from the root of Platycodon grandiflorum (AEPG) on the cell growth and apoptosis in human lung carcinoma cell line A549. Exposure of A549 cells to AEPG resulted in growth inhibition and induction of apoptosis in a dose-dependent manner as measured by hemocytometer counts, fluorescence microscopy and flow cytometry analysis. This increase in apoptosis was associated with a decrease in Bcl-2 expression, an increase of Bax and an activation of caspase-3. AEPG treatment markedly inhibited the activity of telomerase in a dose-dependent fashion. Additionally, the expression of human telomerase reverse transcriptase (hTERT), a main determinant of the telomerase enzymatic activity, was progressively down-regulated by AEPG treatment. These findings suggest that the apoptotic events by AEPG were associated with the diminished telomerase activity and down-regulation of Bcl-2 expression.