5-methylcytosine attack by hydroxyl free radicals and during carbon tetrachloride promoted liver microsomal lipid peroxidation: Structure of reaction products

We recently reported that trichloromethyl and trichloromethylperoxyl radicals attack 5-methylcytosine (5MC) to give several products derived from hydroxylation, deamination or halogenation reactions. Hydroxyl radicals and lipid peroxidation (LP) are more frequently involved in deleterious pathological or toxicological processes than those CCl4 derived radicals and thus we considered it of interest to test whether they also alter 5MC. We observed that OH radicals generated by 0.1 mM Fe2+/2.5 mM H2O2 at 25 degrees C for 1 h led to the production of 5-hydroxymethylcytosine (5HMC), When (OH)-O-. generation was performed with UV light (254 nn, 3400 mu Watt/cm(2)) and 2 mM H2O2 during 4 min at 25 degrees C the following products were observed: 5-hydroxy-5-methylhydantoin, 5-hydroxyhydantoin, 5HMC, thymine glycol (two isomers) and 5-hydroxymethyl-6-hydroxycytosine. When 5MC was exposed to liver microsomal suspensions in the presence of NADPH generating system and carbon tetrachloride during 1 h at 37 degrees C and under air, the formation of only SHMC was observed. Detection and identification of all reaction products was done by GC/MS analysis of trimethylsilyl derivatives of the bases. If similar reactions occurred in DNA, these results might be of relevance to gene control, differentiation and carcinogenesis.