title: The olive leaf extract oleuropein exerts protective effects against oxidant-induced cell death, concurrently displaying pro-oxidant activity in human hepatocarcinoma cells.
abstract: OBJECTIVE
  Oleuropein (OP), the predominant natural constituent of leaves of the olive tree, exerts anti-inflammatory and antioxidant effects. The purpose of this study was to assess the protective effects of OP under the conditions of paraquat (PQ)-induced oxidative stress in vitro, using the human hepatocarcinoma cell line, HepG2.
  
  
  METHODS
  Cell viability and death were determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and 4',6-diamidino-2-phenylindole-propidium iodide staining, respectively. Superoxide anion and lipid peroxidation levels were evaluated using nitroblue tetrazolium and thiobarbituric acid-reactive substances assays, respectively. Apoptosis was assessed by measuring poly(ADP-ribose) polymerase (PARP) and caspase-3 (Casp-3) cleavage via immunoblotting and immunofluorescence analyses.
  
  
  RESULTS
  PQ induced a decrease in cellular viability by promoting necrosis through a mechanism involving superoxide generation and nuclear translocation of cleaved Casp-3. Co-treatment with OP afforded significant protection against the suppressive effects of PQ, as evident from increased cell viability, reduction of Casp-3 immunofluorescence, and normalization of β-tubulin expression levels. Unexpectedly, these OP-mediated protective effects were associated with increased superoxide and malondialdehyde generation and PARP cleavage.
  
  
  CONCLUSIONS
  OP protects HepG2 cells against PQ-induced necrosis by suppressing Casp-3 cleavage while concomitantly acting as a pro-oxidant agent. This paradoxical mechanism of action of OP requires further investigation.
authors: a Institute of Biosciences and Applications, National Center for Scientific Research 'Demokritos' , Athens , Greece.
authors: Elias N
authors: EN
authors: Katsoulieris
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3 / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D006801:Humans; D057888:Iridoid Glucosides; D039823:Iridoids / Q000494:pharmacology*; D015227:Lipid Peroxidation / Q000187:drug effects; D031658:Olea / Q000737:chemistry*; D010936:Plant Extracts / Q000737:chemistry* / Q000494:pharmacology; D018515:Plant Leaves / Q000737:chemistry*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism
chemical_list: D057888:Iridoid Glucosides; D039823:Iridoids; D010936:Plant Extracts; D017382:Reactive Oxygen Species; D013481:Superoxides; C002769:oleuropein; D053148:Caspase 3
keywords: Apoptosis; Hydroxyl radical; Lipid peroxidation; Necrosis; Oleuropein; Oxidative stress; Paraquat; Superoxide