The effect of Longan seed polyphenols on colorectal carcinoma cells

Abstract

Polyphenol-rich longan seed extract (LSP) is a free radical scavenger and antioxidant. However, the effect of LSP on the growth of human colorectal carcinoma cells (CRC) has not yet been evaluated. Polyphenols of longan seeds were extracted and measured by colorimetry. Four CRC cell lines (Colo 320DM, SW480, HT-29 and LoVo) were treated with LSP and assessed for viability by trypan blue exclusion, for cell cycle distribution by flow cytometry, for apoptosis by annexin V labelling and for changes in the levels of proteins involved in cell cycle control or apoptosis by immunoblotting. Total phenol content of LSP was 695 mg g(-1) and total flavonoids were 150 mg g(-1). LSP inhibited the proliferation (25 microg mL(-1)-200 microg mL(-1)) of Colo 320DM, SW480 and HT-29, but not LoVo. LSP inhibited the proliferation by blocking cell cycle progression during the DNA synthesis phase and inducing apoptotic death. Western blotting indicated that LSP blocks the S phase, reducing the expression of cyclin A and cyclin D1. Colo 320DM and SW480 treated with LSP also showed the activation of caspase 3 and increased Bax : Bcl-2 ratio. LSP induces S phase arrest of the cell cycle and apoptotic death in three CRC cell lines. The results indicate that LSP is a potential novel chemoprevention and treatment agent for colorectal cancer.