Degradation of deoxyribonucleic acid by a 1,10-phenanthroline-copper complex: the role of hydroxyl radicals

Abstract

Degradation of deoxyribonucleic acid (DNA) by 1,10-phenanthroline has been shown to require Cu(II), a reducing agent, and O2. Other metal ions do not substitute for Cu(II), and degradation of DNA is inhibited by metal ions that can form stable complexes with 1,10-phenanthroline, such as Co(II), Cd(II), Ni(II), or Zn(II), as well as by chelators that can bind copper, such as triethyltetraamine, neocuproine, or ethylenediaminetetraacetic acid (EDTA). Neocuproine, a specific copper chelator, is more effective than EDTA in inhibiting the breakdown of DNA. The degradation of DNA shows a requirement for a reducing agent which can be satisfied by either ascorbate or a thiol. A free radical generating system, e.g., xanthine oxidase-hypoxanthine, can substitute for the reducing agent. DNA degradation, in the presence of either an organic reducing agent or xanthine oxidase-hypoxanthine, is inhibited by hydroxyl radical scavengers and by catalase, suggesting that hydroxyl radical is the reactive species in DNA degradation and that hydrogen peroxide is an intermediate in hydroxyl radical generation.

Oxidation of the sugar moiety of DNA by ionizing radiation or bleomycin could induce the formation of a cluster DNA lesion

“…Indeed, bleomycin specifically oxidizes the 4-position of 2-deoxyribose, whereas calicheamicin attacks preferentially the 4-and 5-positions, and neocarzinostatin is implicated in 1-, 4-, and 5-oxidation reactions (6). Moreover, cationic metal porphyrins (7) or other artificial nucleases such as bis(1,10-phenanthroline)copper(I) (8) are also able to oxidize the sugar moiety of DNA. Altogether, these data underline the importance of sugar alterations and also the diversity of the oxidation pathways.…”

Research communication copper-1,10-phenanthroline induces internucleosomal DNA fragmentation in HepG2 cells, resulting from direct oxidation by the hydroxyl radical

“…Although the ability of Cu II (OP) # to act as a chemical nuclease via the promotion of dOH formation has been reported extensively [19][20][21], the laddering of the DNA fragments in agarose gels reported here is more commonly associated with the activity of endonucleases [1][2][3]7,11,14]. Incubation of HepG2 cells with Cu II (OP) # caused cell killing (Table 1) and the detection of 8-OHdG in the DNA confirmed attack by dOH (Table 2) [17,25].…”

“…With this in mind, we embarked upon a study of DNA fragmentation in HepG2 cells exposed to the copper(II) complex of 1,10-phenanthroline (o-phenanthroline, OP), Cu II (OP) # . In the presence of a reducing agent, Cu II (OP) # is known to promote hydroxyl radical formation from molecular oxygen by redoxcycling, and was therefore considered to be a suitable agent for the stimulation of ROS formation [19][20][21][22]. We demonstrate that internucleosomal DNA fragmentation is induced in exposed cells, and that although this is suppressed if incubations are carried out at 4 mC (indicating a requirement for enzyme activity), this is due entirely to hydroxyl radical attack upon the DNA, demonstrating that internucleosomal DNA fragmentation cannot be used alone to distinguish between apoptosis and other forms of cell killing.…”

Radiation-Induced Double-Strand Modification in Calf Thymus DNA in the Presence of 1,2-Dihydroxy-9,10-Anthraquinone and Its Cu(II) Complex

“…They indicate that these complexes are effective cleaving DNA (27). Results indicate that the cuprous complex of these ligands formed during the course of reaction binds to DNA and that subsequent oxidation by H202 causes site-specific damage due to formation of the OH at the binding site (27)(28)(29).…”

“…However, the transfer of the electron from the radical center at C-5 or C-6 certainly depends on the redox couple of the quinone and its corresponding semiquinone. (27)(28)(29).…”