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

• Published in: Chemico-biological interactions 1996-01, Vol.99 (1), p.289-299
• Main Authors: Castro, Gerardo D, Díaz Gómez, María I, Castro, JoséA
• Format: Article
• Language: English
• Subjects: 5-Methylcytosine; Animals; Carbon tetrachloride; Carbon Tetrachloride - pharmacology; Cytosine - analogs & derivatives; Cytosine - metabolism; DNA methylation; Free radicals; Free Radicals - metabolism; Free Radicals - pharmacology; Gas Chromatography-Mass Spectrometry; Hydantoins - metabolism; Hydrogen Peroxide - metabolism; Hydroxyl Radical - metabolism; Iron - metabolism; Lipid peroxidation; Lipid Peroxidation - drug effects; Male; Microsomes, Liver - drug effects; Microsomes, Liver - metabolism; Molecular Structure; Rats; Rats, Sprague-Dawley; Ultraviolet Rays
• ISSN: 0009-2797; 1872-7786
• DOI: 10.1016/0009-2797(95)03680-6

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 CCl 4 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 Fe 2+/2.5 mM H 2O 2 at 25 °C for 1 h led to the production of 5-hydroxymethylcytosine (5HMC). When OH generation was performed with UV light (254 nm, 3400 μWatt/cm 2) and 2 mM H 2O 2 during 4 min at 25 °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 °C and under air, the formation of only 5HMC 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.