Hydroxycinnamic Acids Act As The DNA-cleaving Agents In The Presence Of Cu(Ⅱ) Ions: Mechanism, Structure-activity Relationship And Biological Implication

The important role of hydroxycinnamic acids(HCAs),i.e.,caffeic acid(CaA), chlorogenic acid(ChA),sinapic acid(SA),ferulic acid(FA),3-hydroxycinnamic acid (3-HCA) and 4-hydroxycinnamic acid(4-HCA) as the pBR322 plasmid DNA-Cleaving agents in the presence of Cu(â…¡) ions was investigated.It was found that the compounds o-dihydroxyl and o-dimethoxyhydroxyl groups(CaA,SA and ChA) exhibited remarkably higher activity in the DNA damage than the ones bearing no such groups,and CaA was the most active one among the examined HCAs.The involvement of reactive oxygen species and Cu(â… ) ions in the DNA damage was affirmed by the inhibition of DNA breakage using specific scavengers of activated oxygen and Cu(â… ) chelator.The interaction between CaA and Cu(â…¡) and influence of ethylenediaminetetraacetic acid,solvent and pH on the interaction were also studied to help elucidate the detailed prooxidant mechanism using UV-visible spectroscopy, demonstrating that it is CaA phenolate anion,instead of the parent molecule,chelates with Cu(â…¡) as a bidentate ligand,hence facilitating intramolecular electron transfer between CaA and Cu(â…¡).The formation of CaA o-quinone in the presence of Cu(â…¡) plays a pivotal role in the DNA damage and the radical intermediate was also proved by the dimer of CaA obtained in the presence of Cu(â…¡).Of note,CaA was also the most cytotoxic one among the examined HCAs on HL-60 cell proliferation.Addition of Cu(â…¡) resulted in the effect dichotomy on cell viability depending on the concentration of CaA,that is,at low doses CaA enhanced the cell viability;conversely,at high doses CaA almost completely inhibited the cell proliferation.On the other hand,when superoxide dismutase was added beforehand, the two stimulation effects of Cu(â…¡) were significantly ameliorated,clearly indicates that oxidative stress level regulates cell proliferation and death.This provided the directed evidence for prooxidant cancer chemopreventive action.