Antioxidant interactions among hydrophilic and lipophilic dietary phytochemicals based on inhibition of low-density lipoprotein and DNA damage

Antioxidant interaction among hydrophilic phytochemicals (caffeic acid, p-coumaric acid) and lipophilic phytochemicals (beta-carotene, lycopene) in different mole ratios (n/n, 1:9, 3:7, 5:5, 7:3, 9:1) was evaluated. Assays performed were based on the scavenging activity of hydrogen peroxide (H2O2), the inhibition of low-density lipoprotein oxidation (ox-LDL) and DNA damage in vitro, using isobological analysis, synergistic rate (SR), and combination index (CI). Results showed that groups containing higher ratios of hydrophilic phytochemicals exhibited synergism while those containing higher ratios of lipophilic phytochemicals showed antagonism. Meanwhile, groups containing caffeic acid (e.g., caffeic acid:beta-carotene, 9:1) with more hydroxyl groups showed higher synergism (SR = 0.76 +/- 0.02, CI = 0.77 +/- 0.03) than groups containing p-coumaric acid (e.g., p-coumaric acid:beta-carotene, 9:1, SR = 0.88 +/- 0.04, CI = 0.82 +/- 0.05) on the scavenging activity of H2O2. Groups that contained lycopene (caffeic acid: lycopene, 9:1) with a higher ability of regeneration by phenolic acids showed more significant synergism (SR = 0.70 +/- 0.02, CI = 0.79 +/- 0.03) than groups containing beta-carotene (e.g., caffeic acid:beta-carotene, 9:1, SR = 1.00 +/- 0.03, CI = 0.98 +/- 0.04) on the inhibition of DNA damage. This study provided a basis for antioxidant interactions among phytochemicals against ox-LDL and DNA damage in vivo. In addition, the choice of appropriate ratios and structures of hydrophilic and lipophilic phytochemicals should be considered in the diet and formulation of functional foods.