Alkyl hydroxytyrosyl ethers show protective effects against oxidative stress in HepG2 cells

Alkyl hydroxytyrosyl ethers (methyl, ethyl, propyl, and butyl ethers) have been synthesized from hydroxytyrosol (HTy) in response to the increasing food industry demand of new lipophilic antioxidants. Having confirmed that these compounds reach portal blood partially unconjugated and thus are effectively absorbed, their potential antioxidant activity was evaluated in the human hepatocarcinoma cell line (HepG2). The effects of 0.5-10 μM alkyl hydroxytyrosyl ethers on HepG2 cell integrity and redox status were assessed as well as the protective effect against oxidative stress induced by tert-butylhydroperoxide (t-BOOH). Cell viability (Crystal violet) and cell proliferation (BrdU assay) were measured as markers of cell integrity, concentration of reduced glutathione (GSH), generation of reactive oxygen species (ROS), and activity of antioxidant enzymes glutathione peroxidase (GPx) and glutathione reductase (GR) as markers of redox status and determination of malondialdehyde (MDA) as a marker of lipid peroxidation. Direct treatment of HepG2 with alkyl hydroxytyrosyl ethers induced slight changes in cellular intrinsic antioxidants status, reducing ROS generation and inducing changes in GPx and GR activities. Pretreatment of HepG2 cells with alkyl hydroxytyrosyl ethers counteracted cell damage induced by t-BOOH, partially after 2 h and completely after 20 h, by increasing GSH and decreasing ROS generation, MDA levels, and antioxidant enzyme (GPx and GR) activity. According to these results the alkyl hydroxytyrosyl ethers show clear protective effects against oxidative stress, related to their lipophilic nature, that are similar to or even higher than those of their precursor, HTy.