DNA strand breaking by the carbon-centered radical generated from 4-(hydroxymethyl) benzenediazonium salt, a carcinogen in mushroom Agaricus bisporus.

4-(Hydroxymethyl)benzenediazonium salt (HMBD), a carcinogen in mushroom Agaricus bisporus, was found to generate a carbon-centered radical, 4-(hydroxymethyl)phenyl radical, during incubation at pH 7.4 and 37 degrees C, when estimated by Electron Spin Resonance (ESR) spin-trapping technique using 5,5-dimethyl-1-pyrroline N-oxide (DMPO), N-tert-butylphenyl-alpha-nitrone (PBN) and 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS). Formation of a substantial amount of benzyl alcohol during incubation of HMBD in the presence of a hydrogen donor, ethanol, supported the generation of the carbon-centered radical. When plasmid supercoiled DNA was incubated with HMBD at pH 7.4 and 37 degrees C for 30 min, the supercoiled DNA was converted into a nicked circular relaxed form and subsequently into a linear form. Sequence analysis indicated that the compound cleaved the plasmid DNA strand non-specifically. The intracellular double stranded DNA of Escherichia coli was fragmented by the compound, which may be responsible for its cytotoxicity. The compound induced mouse micronucleated peripheral reticulocytes. The compound was active in breaking DNA strands in the absence of molecular oxygen and in the presence of superoxide dismutase and catalase, indicating that no oxygen-derived radicals participated in the breaking. DNA breaking was inhibited by hydrogen donors butyl hydroxyanisole and ethanol, thiol compounds L-cysteine and 2-mercaptoethanol, and spin-trapping agents DMPO and PBN, indicating the direct contribution of the carbon-centered radical to the breaking.