Green coffee hydroxycinnamic acids but not caffeine protect human HepG2 cells against oxidative stress

The intake of green coffee has been associated with a lower risk of diseases of oxidative etiology probably due to its high phenolic content. The present study investigated the effect of treating human HepG2 cells with different concentrations of a green coffee bean extract (GCBE) and its main hydroxycinnamic acids, 5-caffeoylquinic acid (5-CQA) and 3,5-dicaffeoylquinic acid (3,5-DCQA), and the methylxanthine caffeine (CAF), directly or prior to inducing an oxidative stress by incubating cells with 400. μM tert-butylhydroperoxide (t-BOOH). Direct treatment with GCBE (1-50. μg/mL), 5-CQA and 3,5-DCQA (1-40. μM) significantly decreased reactive oxygen species (ROS) production by HepG2 cells. Pre-treatment with GCBE, 5-CQA and 3,5-DCQA for 20. h prevented the cellular and macromolecular damage induced by t-BOOH, returning glutathione levels and the activity of antioxidant enzymes to values similar to control cells. Moreover, the increased ROS generation induced by t-BOOH was dose-dependently prevented when cells were pre-treated with GCBE, 5-CQA and 3,5-DCQA. CAF showed no protective effect. It can be concluded that GCBE and its main polyphenols, 5-CQA and 3,5-DCQA, but not caffeine, confer a significant protection against oxidative stress in vitro.