GENOTOXICITY OF PHOTOILLUMINATED RIBOFLAVIN IN THE PRESENCE OF CU(II)

Riboflavin is known to generate superoxide anion (O-2(.-)) and other r eactive oxygen species in the presence of Cu(II) and light as well as cause fragmentation of DNA and protein in vitro. In the present study we examined the genotoxic effects of photoilluminated riboflavin in th e presence of Cu(II). Using the phage inactivation assay, a significan t decline in plaque-forming unit (PFU) is seen. Results of Ames testin g have suggested that probably a frameshift mutation is caused by a ri boflavin-Cu(II)-mediated reaction. Using neocuproine as a Cu(I) seques tering reagent, Cu(I) has been shown to be an essential intermediate g enerated in the reaction between Cu(II), photoilluminated riboflavin, and DNA, Results obtained with various scavengers of active oxygen spe cies strongly suggest that the species predominantly responsible for D NA damage is oxygen (O-2) in the singlet or triplet state, together wi th H2O2 hydroxyl radical, and hydroxyl ion, to a lesser extent. In the case of riboflavin, a ternary complex of DNA-drug-Cu(II) is presumabl y formed. A redox reaction, involving riboflavin and Cu(II) in the com plex, may then occur with the formation of a DNA-oxidized riboflavin-C u(I) complex. This probably acts as a catalyst for the oxidation of Cu (I) to Cu(II), during which molecular oxygen is reduced to generate a variety of active oxygen species. The probable mechanism for the gener ation of these reactive oxygen species has also been proposed.