Phenolic extract from oleaster (Olea europaea var. Sylvestris) leaves reduces colon cancer growth and induces caspase-dependent apoptosis in colon cancer cells via the mitochondrial apoptotic pathway

PLoS One. 2017 Feb 17;12(2):e0170823. doi: 10.1371/journal.pone.0170823. eCollection 2017.

Abstract

Dietary polyphenols, derived from natural products, have received a great interest for their chemopreventive properties against cancer. In this study, we investigated the effects of phenolic extract of the oleaster leaves (PEOL) on tumor growth in mouse model and on cell death in colon cancer cell lines. We assessed the effect of oleaster leaf infusion on HCT116 (human colon cancer cell line) xenograft growth in athymic nude mice. We observed that oleaster leaf polyphenol-rich infusion limited HCT116 tumor growth in vivo. Investigations of PEOL on two human CRC cell lines showed that PEOL induced apoptosis in HCT116 and HCT8 cells. We demonstrated an activation of caspase-3, -7 and -9 by PEOL and that pre-treatment with the pan-caspase inhibitor, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (z-VAD-fmk), prevented PEOL-induced cell death. We observed an involvement of the mitochondrial pathway in PEOL-induced apoptosis evidenced by reactive oxygen species (ROS) production, a decrease of mitochondrial membrane potential, and cytochrome c release. Increase in intracellular Ca2+ concentration induced by PEOL represents the early event involved in mitochondrial dysfunction, ROS-induced endoplasmic reticulum (ER) stress and apoptosis induced by PEOL, as ruthenium red, an inhibitor of mitochondrial calcium uptake inhibited apoptotic effect of PEOL, BAPTA/AM inhibited PEOL-induced ROS generation and finally, N-acetyl-L-cysteine reversed ER stress and apoptotic effect of PEOL. These results demonstrate that polyphenols from oleaster leaves might have a strong potential as chemopreventive agent in colorectal cancer.

MeSH terms

  • Animals
  • Apoptosis / drug effects*
  • Caspases / metabolism*
  • Cell Death / drug effects
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Colonic Neoplasms / pathology*
  • Endoplasmic Reticulum Stress / drug effects
  • Gene Expression Regulation, Neoplastic / drug effects
  • Humans
  • Membrane Potential, Mitochondrial / drug effects
  • Mice
  • Mice, Nude
  • Mitochondria / drug effects*
  • Mitochondria / pathology
  • Olea / chemistry*
  • Phenol / chemistry
  • Plant Extracts / pharmacology*
  • Plant Leaves / chemistry*
  • Reactive Oxygen Species / metabolism
  • Transcription Factor CHOP / metabolism
  • Xenograft Model Antitumor Assays

Substances

  • DDIT3 protein, human
  • Plant Extracts
  • Reactive Oxygen Species
  • Transcription Factor CHOP
  • Phenol
  • Caspases

Grants and funding

This study was supported by Inserm, Labex LipSTIC INSERM U866, bilateral Franco-Algerian collaborative project “Tassili.”