Effect of natural phenolic acids on DNA oxidation in vitro

We examined the antioxidant activity of the following natural phenolic comp ounds present in food: 3-OH-benzoic acid (3-OH-BA): 4-OH-benzoic acid (4-OH -BA): 2,3-dihydroxybenzoic acid (2,3-diOH-BA); 3,4-dihydroxybenzoic acid (3 ,4-diOH-BA or protocatechuic acid); ferulic acid; caffeic acid; and 2-couma ric, 3-coumaric and 4-coumaric acids. We measured the inhibitory effect of these compounds on iron-dependent oxidative DNA damage in vitro [incubating herring sperm DNA with Fe(lll)/GSH] or using cumene hydroperoxide (CumOOH) as a free-radical generating system; we also studied the interaction of th ese phenols with Fe(II) or Fe(III) spectrophotometrically. Among the tested compounds, 2,3-diOH-BA, 3,4-diOH-BA and caffeic acid interacted with Fe(II .) and showed a potent inhibitory effect on iron-induced oxidative DNA dama ge. CumOOH-induced DNA oxidation was not modified by these compounds. On th e contrary, 2-coumaric, 3-coumaric and 4-coumaric acids did not interact wi th iron but protected against oxidative DNA damage induced by Fe(III)/GSH a nd by CumOOH, indicating a direct free-radical scavenging activity of these compounds in both systems. The IC50+/-S.E.M. of the three coumaric acids a gainst CumOOH-induced DNA oxidation was 44.2 +/-2.0, 54.7 +/-2.0 and 33.1 /-1.0 muM, respectively. On the contrary, 3-OH-BA and 4-OH-BA did not have scavenging activity and 3-OH-BA actually enhanced oxidative DNA damage. In conclusion, some natural phenolic acids, commonly present in food, have int eresting protective activity against DNA oxidation in vitro and deserve fur ther consideration as effective antioxidants in vivo. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.