Phenolic compounds protect HepG2 cells from oxidative damage: Relevance of glutathione levels

In the present work, the potential hepatoprotective effects of five phenolic compounds against oxidative damages induced by tert-butyl hydroperoxide (t-BHP) were evaluated in HepG2 cells in order to relate in vitro antioxidant activity with cytoprotective effects. t-BHP induced considerable cell damage in HepG2 cells as shown by significant LDH leakage, increased lipid peroxidation, DNA damage as well as decreased levels of reduced glutathione (GSH). All tested phenolic compounds significantly decreased cell death induced by t-BHP (when in co-incubation). If the effects of quercetin are given the reference value 1, the compounds rank in the following order according to inhibition of cell death: luteolin (4.0)> quercetin (1.0)> rosmarinic acid (0.34)> luteolin-7-glucoside (0.30)> caffeic acid (0.21). The results underscore the importance of the compound's lipophilicity in addition to its antioxidant potential for its biological activity. All tested phenolic compounds were found to significantly decrease lipid peroxidation and prevent GSH depletion induced by t-BHP, but only luteolin and quercetin significantly decreased DNA damage. Therefore, the lipophilicity of the natural antioxidants tested appeared to be of even greater importance for DNA protection than for cell survival. The protective potential against cell death was probably achieved mainly by preventing intracellular GSH depletion. The phenolic compounds studied here showed protective potential against oxidative damage induced in HepG2 cells. This could be beneficial against liver diseases where it is known that oxidative stress plays a crucial role. (c) 2006 Elsevier Inc. All rights reserved.