Palladium or platinum exacerbates hydroxyl radical mediated DNA damage

Strand breakage of supercoiled pBR322 DNA by a Fenton system is increased in the presence of palladium (Pd) or platinum (Pt) ions. Neither Pd nor Pt ions can substitute for iron in the Fenton system. We have obtained several lines of evidence that Pd and Pt ions in the presence of a Fenton system can augment the production of OH(·), as monitored by a spectrophotometric method quantifying hydroxylated salicylate or by a fluorometric method quantifying catechol production. Furthermore, the promoting effect of both metal ions on OH(·) production was substantiated by the identification of multiple hydroxylated products of salicylate [2,3- dihydroxybenzoate (A). 2,5-dihydroxybenzoate (B), and catechol (C)] using HPLC. The concentrations of A, B, and C produced in the control were 4.5, 8.0, and 2.0 μM, respectively; whereas, their respective concentrations increased to 23.6, 42.0, and 10.0 μM with the addition of Pd ions. The observed phenomenon was further confirmed by the identification of HO-DMPO spin adducts using ESR spectroscopy. Taken together, our data suggest that the mechanism of Pd or Pt ion-mediated exacerbation of DNA damage by a Fenton system is due to the promotion of OH(·) production by these metal ions.