Interaction of trichloromethyl free radicals with thymine in a model system: a mass spectrometric study

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 H202 at 25 degrees C for 1 h led to the production of 5-hydroxymethylcytosine (5MHC). When OH generation was performed with UV light (254 nm, 3400 muWatt/cm2) and 2mM H202 during 4 min at 25 degrees C the following products were observed: 5-hydroxy-5-methylhydantoin, 5-hydroxyhydantoin, 5MHC, 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 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.

Reaction of bromotrichloromethane derived free radicals with uracil in a model system. Structures of products formed

Free radicals generated by benzoyl peroxide-mediated catalytic decomposition of bromotrichloromethane (eg. trichloromethyl) were allowed to react under nitrogen or under air with uracil. Under nitrogen two reaction products were formed, one was identified as 5-chlorouracil and the other as a 5-bromouracil. Under air, besides the above two products other nine were also formed: 5,6-dihydrouracil; 5-hydroxyuracil; a chlorohydroxy adduct of uracil; a bromohydroxy derivative of uracil having the 5,6 bond in the saturated form; other bromohydroxy derivative of uracil having the double bond intact; 5,6-dihydroxyuracil; two dihalogenated hydroxylated uracil derivatives and one peak we were not able to descipher its structure. No single reaction product formed had carbon centered radicals (eg. trichloromethyl) added from CBrCl3 and consequently would be missed in 'in vivo' covalent binding studies where 14C haloalkane (CBrCl3 or carbon tetrachloride) were employed. If similar reaction products resulted during interaction of CBrCl3 reactive metabolites with uracil in RNAs, significant deleterious effects in their function would be expected. That possibility, however, remains to be established.

Proline interaction with trichloromethyl and trichloromethyl peroxyl free radicals in a model system: studies about the nature of the reaction products formed

Trichloromethyl and trichloromethyl peroxyl radicals are known to be produced during CCl4 biotransformation and are considered to be critical for deleterious effects of this haloalkane. In this work we describe our studies on the interaction of both free radicals with a lipid-soluble derivative of the amino acid proline in a model system. The analysis of the reaction products formed by gas chromatography-mass spectrometry of the sylilated derivatives revealed the formation of at least 11 reaction products under anaerobic conditions and 13 under aerobic atmosphere. All of them were tentatively identified and all but 2 were proline analogs. Only 3 incorporated in their structure CCl3 or CCl2 portions of the CCl4 molecule and, consequently, most of the adducts formed would be missed during regular procedures most toxicologists use to determine CCl4. Results were analyzed in relation to the known role of proline in collagen metabolism and of this protein in liver cirrhosis.

5-methylcytosine attack by free radicals arising from bromotrichloromethane in a model system: structures of reaction products

The interaction between free radicals derived from the catalytic decomposition of bromotrichloromethane and 5-methylcytosine (5MC) under different conditions were studied. The structures of the reaction products formed was established by the GC/MS analysis of their trimethylsilyl derivatives. Under anaerobic conditions, the formation of the following products was found: (1) thymine; (2) 5-hydroxymethyl uracil. Under aerobic conditions, the following reaction products were identified: (1) The same two products formed under anerobic conditions. (2) Monohydroxylated thymine. Precise location of the hydroxyl group was not established but probably corresponds to the six position isomer. (3) Two monochloro monohydroxy thymines. It is suggested that they are cis-trans isomers whose substituents are located at the 5-methyl and six positions of the base. (4) The trimethylsilyl derivative of thymine glycol. (5) Two monobromo monohydroxy adducts of thymine. One of them was detected as its underivatized form in the hydroxyl group position. (6) A partially silylated dihydroxythymine. When benzoyl peroxide was omitted from aerobic incubation mixtures, the compounds formed changed. No longer observable were: thymine; the two monochloro monohydroxy derivatives of thymine; thymine glycol, and one monohydroxythymine. On the other hand, two new reaction products were formed instead: a partially silylated monochloro-monohydroxy thymine and 5-hydroxymethyl-cytosine. If similar or equivalent reaction products were formed in DNA during CBrCl3 or CCl4 poisoning, results might be of relevance, because the 5MC content in DNA from eukaryotes is related to differentiation, gene control, and to carcinogenesis.