The sterols isolated from evening primrose oil inhibit human colon adenocarcinoma cell proliferation and induce cell cycle arrest through upregulation of LXR

• PS-EPO were found to be a potent antiproliferative agent in a dose- and time- dependent manner.
• PS-EPO exerted a stimulatory effect on apoptosis and necrosis, increasing the number of cells in G0/G1 phase.
• PS-EPO produced a significant upregulation in liver X receptor (LXR) gene expression.

Evening primrose oil (EPO) is widely used as a dietary supplement from which beneficial effects have been reported in rheumatic and arthritic conditions, atopic dermatitis, psoriasis, premenstrual and menopausal syndrome, and diabetic neuropathy. The aim of this study was to determine whether phytosterols isolated from evening primrose oil (PS-EPO), and its main components β-sitosterol and campesterol, affect proliferation, cell death, and the cell cycle of human colon adenocarcinoma (HT-29) cells. PS-EPO were a potent antiproliferative agents in a dose- and time-dependent manner, with an IC50 of 62.9 µg/mL after 48 h, lower than β-sitosterol and campesterol (79.0 µM and 71.6 µM respectively). Flow cytometry showed that PS-EPO exerted a stimulatory effect on apoptosis and necrosis, increasing the number of cells in G0/G1 phase. PS-EPO produced a significant upregulation in liver X receptor (LXR) gene expression that may be one of the principal mechanisms of the tumor shrinkage by PS-EPO.