Antioxidant and Hepatoprotective Effects of Artichoke Extracts and Constituents in Cultured Rat Hepatocytes

Primary cultures of rat hepatocytes exposed to tert-butyl hydroperoxide (t-BHP) were used for characterizing the antioxidative and hepatoprotective potential of aqueous artichoke extracts (AK.) and some selected constituents. Addition of t-BHP to the culture medium resulted in enhanced lipid peroxidation measured as production of malondialdehyde (MDA) and enhanced cytotoxicity detected by LDH leakage. Aqueous artichoke extracts added prior or simultaneously with t-BHP reduced both phenomena with EC(50) values of about 95 and 12 mug artichoke powder/ml, respectively. Furthermore, AE prevented the loss of intracellular GSH caused by t-BHP. Several polyphenolic and flavonoid constituents of AE were found to reduce MDA production. EC(50) values were 8.1, 12.5, 15.2, 28 mug/ml for caffeic acid, chlorogenic acid, cynarin and cynarosid, respectively. A similar ranking for AE and constituents was found when using the chemiluminescent xanthine oxidase assay for determination of the antioxidative potency, but EC(50) values were consistently lower. Concerning the hepatoprotective effect, that is prevention of LDH leakage, all constituents were almost equipotent and EC(50) values were lower than for MDA production. These results suggest (i) that lipid peroxidation is not the primary cause for cytotoxicity of t-BHP, (ii) that hepatocyte cultures exposed to t-BHP represent a suitable model system for screening plant extracts for antioxidant and hepatoprotective effects, and (iii) that AE have a marked antioxidative and hepatoprotective potential which can be ascribed, at least partially, to some ubiquitous and artichoke-specific polyphenolic and flavonoid compounds.