Influence of flavan-3-ols and procyanidins on UVC-mediated formation of 8-oxo-7,8-dihydro-2′-deoxyguanosine in isolated DNA

The flavan-3-ols (-)-epicatechin (epicatechin) and (+)-catechin (catechin) and their related oligomers (procyanidins) isolated from cocoa were assayed for their capacity to inhibit the UVC-mediated formation of 8-oxo-7,8-dihydro-2′-deoxyguanosine (oxo⁸dG) in calf thymus DNA. The above-mentioned compounds inhibited oxo⁸dG production in a concentration- and time-dependent manner. After 30 min of irradiation (30 kJ/m²), 0.1, 1.0, 10, and 100 μM epicatechin inhibited oxo⁸dG formation by 20, 36, 64, and 74%, respectively. For the same dose of UVC, 0.1, 1.0, 10, and 100 μM catechin inhibited oxo⁸dG formation by 1, 23, 50, and 70%, respectively. Epicatechin was more efficient than catechin with respect to inhibiting oxo⁸dG formation (IC₅₀ 1.7 ± 0.7 vs 4.0 ± 0.7 μM). Monomer, tetramer, and hexamer fractions were equally effective in inhibiting oxo⁸dG formation when assayed at 10 μM monomer equivalent concentration. At similar concentrations (1-50 μM), the inhibition of the UVC-mediated oxo⁸dG formation by flavan-3-ols and procyanidins was in the range of that of α-tocopherol, Trolox, ascorbate, and glutathione. These results support the concept that flavan-3-ols and their related procyanidins can protect DNA from oxidation at concentrations that can be physiologically relevant. Both epimerism and degree of oligomerization are important determinants of the antioxidant activity of flavan-3-ols and procyanidins.