Alaternin and emodin with hydroxyl radical inhibitory and/or scavenging activities and hepatoprotective activity on tacrine-induced cytotoxicity in HepG2 cells

The antioxidative and hepatoprotective potentials of two anthraquinones, alaternin (2-hydroxy-emodin) and emodin, to scavenge and/or inhibit hydroxyl radicals generated by the Fenton reaction and to protect tacrine-induced cytotoxicity in human liver derived HepG2 cells were evaluated, respectively. The inhibitory activity on hydroxyl radical generated in a cell-free chemical system (FeSO₄/H₂O₂) was investigated by a fluorescence spectrophotometer using a highly fluorescent probe, 2′,7′-dichlorofluorescein. The hydroxyl radical scavenging activity was determined by electron spin resonance spectroscopy using 5,5-dimethy-1-pyrroline-N-oxide as hydroxyl radicals trapping agents. Tacrine-induced HepG2 cell toxicity was determined by a 3-[4,5-dimethylthiazole- 2yl]-2,5-diphenyltertrazolium bromide assay. Although the scavenging activity of alaternin on hydroxyl radical was similar to that of emodin in dose-dependent patterns, the inhibitory activity exhibited by the former on hydroxyl radical generation was stronger than that of the latter, with IC50 values of 3.05 ± 0.26 μM and 13.29 ± 3.20 μM, respectively. In addition, the two anthraquinones, alaternin and emodin showed their hepatoprotective activities on tacrine-induced cytotoxicity, and the EC₅₀ values were 4.02 μM and 2.37 μM, respectively. Silymarin, an antihepatotoxic agent used as a positive control exhibited the EC₅₀ value of 2.00 μM. These results demonstrated that both alaternin and emodin had the simultaneous antioxidant and hepatoprotective activities.