Characterization of S-[2-(N1-adenyl)ethyl]glutathione as an adduct formed in RNA and DNA from 1,2-dibromoethane

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Abstract
The major DNA adduct derived from 1,2-dibromoethane is known to be S-[2-(N7-guanyl)-ethyl]glutathione; minor nucleic acid DNA adducts were characterized in view of the possibility that some might be unusually persistent or biologically active. RNA was modified in vitro by treatment with 1,2-dibromoethane and glutathione in the presence of rat liver cytosol, and bases were released by mild acid hydrolysis, which liberated > 99% of the bound radioactivity. One of the minor adducts was identified as S-[2-N1-adenyl)ethyl]glutathione on the basis of its UV, mass, and NMR spectra. This adduct could be synthesized by reaction of S-(2-chloroethyl)-glutathione with adenosine. The material was desulfurized by treatment with Raney Ni to give N1-ethyladenine in low yield. The Raney Ni reaction was accompanied by considerable formation of the corresponding N6-adenine derivative via Dimroth rearrangement. Another adduct was identified as S-[2-(N7-guanyl)ethyl]cysteinylglycine by its UV, mass, and NMR spectra, but the material was demonstrated to be formed from the major DNA adduct, S-[2-(N7-guanyl)-ethyl]glutathione under conditions of mild acid hydrolysis. The imidazole ring opened derivative of S-[2-(N7-guanyl)ethyl]glutathione was synthesized and found not to be formed in DNA in vitro or in vivo. The two remaining minor adducts account for 1-2% of the total binding, but insufficient quantities were recovered to allow for structure determination; however, neither of these (uncharacterized) minor products are seen after the reaction of S-(2-chloroethyl)glutathione with guanosine or adenosine. S-[2-(N1-Adenyl)ethyl]glutathione was formed in rat liver RNA and DNA. Rates of loss of the minor adducts from rat liver DNA are very similar to the rate of loss of S-[2-(N1-guanyl)ethyl]glutathione (t1/2 .apprx. 100 h), and no evidence for unusual persistence was found.

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