Polyphenolic extract from coconut kernel modulates apoptotic genes, reactive oxygen species production, and prevents proliferation of human colon cancer cell line

Abstract

Background and Aim: The modern diet along with sedentary lifestyle has led to an increasing mortality rate for colon cancer. Several dietary phytochemicals have been investigated for colon cancer therapy, so as to replace the synthetic drugs having adverse health side effects. The aim of the study was to evaluate the antiproliferative effect of polyphenol-rich fraction from coconut kernel (CK f ) on human colon cancer cell lines (HT-29). Methods: The total flavonoids and polyphenols present in CK f were determined colorimetrically. The cytotoxic and apoptotic effect of CK f was determined using 3-(4,5-dimethyl thiazol-2yl)-2,5-diphenyl tetrazolium bromide assay, acridine orange/ethidium bromide staining, and 4',6-diamidino-2-phenylindole-2 staining. Levels of caspase-3 activity were measured colorimetrically. The expression levels of apoptotic genes BAK, BAX, BID and p53 were measured using real-time polymerase chain reaction. The effect of CK f in inducing reactive oxygen species (ROS) was studied using 2′,7′-dichlorofluorescein diacetate staining. Mitochondrial potential of HT-29 cells treated with CK f was determined by Rhodamine 123 staining. Results: Experimental results showed that CK f contains significant amount of polyphenols. CK f showed cytotoxicity against HT-29 cells (Lethal Dose 50% of 8 μg/ml) by increasing the free radical concentration, caspase 3 enzyme levels, and decreasing the mitochondrial membrane potential in dose-dependent manner. The levels of p53 and BAX showed a major increase in a dose-dependent manner, while BAK gene levels showed a slight but significant increase. Conclusion: These results clearly indicate that coconut kernel which contains cytotoxic phenols affect the growth of colon cancer cells by modulating the apoptotic machinery mediated through mitochondrial ROS production.