Comparison of Quantitative Structure-Activity Relationship and Chemical Antioxidant Activity of beta-Carotene and Lycopene and Their Protective Effects on Intracellular Oxidative Stress

The aim of this study was to determine the chemical and intracellular antioxidant activities of β-carotene and lycopene and to compare their quantitative structure-activity relationship (QSAR). In our previous study, the second ionization energy of lycopene was higher than that of β-carotene, as calculated by QSAR. Chemical antioxidant activities of β-carotene, lycopene, and Trolox were examined by measuring ferric reducing antioxidant power (FRAP) and 2,2'-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. Intracellular antioxidant activities were evaluated by intracellular reactive oxygen species (ROS) and DNA fragmentation. The FRAP of lycopene was higher than that of β-carotene (P less than 0.05), and the two carotenoids had similar antioxidant activities in DPPH radical scavenging activity assay. Trolox had the greatest chemical antioxidant activities (P0.05). When RAW264.7 cells were treated with lipopolysaccharide (LPS) (100 ng/mL) for 20 h, intracellular ROS and DNA fragmentation significantly increased (P less than 0.05). RAW 264.7 cells pretreated with β-carotene (4 μM) and lycopene (0.4~2 μM) for 4 h formed significantly less intracellular ROS than LPS-treated control cells (P less than 0.05), whereas cells with Trolox did not reduce production of intracellular ROS. In addition, cells pretreated with 2 μM lycopene produced less intracellular ROS than those treated with β-carotene (P less than 0.05). DNA fragmentation of cells with β-carotene and lycopene was similar to that of LPS-treated control cells as measured by Hoechst staining. The antioxidant ability of lycopene was greater than that of β-carotene in the QSAR, FRAP, and intracellular ROS assays (P less than 0.05). β-Carotene and lycopene had lower antioxidant activities as measured by FRAP (P less than 0.05) but higher intracellular protective effects against LPS-induced oxidative stress in comparison with Trolox.