Pelargonidin induces apoptosis and cell cycle arrest via a mitochondria mediated intrinsic apoptotic pathway in HT29 cells

Pelargonidin (PE) is an anticancer anthocyanidin that is abundant in berries. In this study, we found that PE irreversibly inhibits human colorectal adenocarcinoma cells (HT29) at micromolar concentrations in a dose- and time-dependent manner, which was determined using the MTT assay, and the GI(50) value was found to be 0.31 mu M for a 24 h exposure. Inverted light microscopy observation and AO/EtBr staining of treated HT29 cells showed apoptotic morphological changes such as chromatin condensation and cell shrinkage. In addition, PE treatment showed a DNA ladder pattern, which is the hallmark of typical intrinsic apoptotic characterization by molecular DNA fragmentation analysis in HT29 cells. PE accumulates cells at G2/M of the cell cycle arrest in a dose-dependent manner as determined by flow cytometry analysis of propidium iodide staining. The G2/M phase cell cycle arrest peak of DNA, characteristic of apoptosis, was observed in the PE-treated cells. In addition, treatment with PE caused the release of cytochrome c from mitochondria into the cytosol. Western blotting analysis showed that PE significantly upregulated the activities of caspase-3 and -9 in comparison with a control group; subsequently, cleavage of PARP-1 protein is suggested, whereas PE significantly downregulated the expression of Bcl-2 and Bcl-xL and upregulated the expression of Bax and Bid. Furthermore, the downregulation of CDC25C, cyclin B1, and CDK1 expression resulted in the induction of G2/M cell cycle arrest in the HT29 cells. In contrast, PE induces the expression of p53 and p21(waf1) in HT29 cells. Collectively, these results show that PE has anticancer activities against HT29 cells through cell cycle arrest, DNA damage, and activation of the mitochondrial signalling pathway. This might provide a potential therapeutic option in the management of colon adenocarcinoma.