Mechanism of synergistic DNA damage induced by caffeic acid phenethyl ester (CAPE) and Cu(II): Competitive binding between CAPE and DNA with Cu(II)/Cu(I).

Caffeic acid phenethyl ester (CAPE) is an active polyphenol of propolis from honeybee hives, and exhibits antioxidant and interesting pharmacological activities. However, in this study, we found that in the presence of Cu(II), CAPE exhibited pro-oxidative rather than antioxidant effect: synergistic DNA damage was induced by the combination of CAPE and Cu(II) together as measured by strand breakage in plasmid DNA and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) formation, which is dependent on the molar ratio of CAPE:Cu(II). Production of Cu(I) and HO from the redox reaction between CAPE and Cu(II), and subsequent OH formation was found to be responsible for the synergistic DNA damage. DNA sequencing investigations provided more direct evidence that CAPE/Cu(II) caused preferential cleavage at guanine, thymine and cytosine residues. Interestingly, we found there are competitive binding between CAPE and DNA with Cu(II)/Cu(I), which changed the redox activity of Cu(II)/Cu(I), via complementary applications of different analytical methods. The observed DNA damage was mainly attributed to the formation of DNA-Cu(II)/Cu(I) complexes, which is still redox active and initiated the redox reaction near the binding site between copper and DNA. Based on these data, we proposed that the synergistic DNA damage induced by CAPE/Cu(II) might be due to the competitive binding between CAPE and DNA with Cu, and site-specific production of OH near the binding site of copper with DNA. Our findings may have broad biological implications for future research on the pro-oxidative effects of phenolic compounds in the presence of transition metals.