{}N-Nitrosobenzylmethylamine Is Activated to a DNA Benzylating Agent in Rats

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Abstract
The ability of rat tissues to activate the esophageal carcinogen, N-nitrosobenzylmethylamine (NBzMA), to a DNA benzylating intermediate was investigated. [3-3H]NBzMA was prepared and given to male F344 rats. Tissues were harvested 4 h after treatment, and DNA was isolated. HPLC analysis with radiochemical detection of chemical and enzymatic hydrolysates of DNA from liver and lung revealed the formation of benzyl adducts. Benzyl alcohol, N2-benzylguanine, 3-benzyladenine, N6-benzyladenine, and 7-benzylguanine were the major radioactive components in the hydrolysates. An unknown adduct was also observed. The adduct distribution was similar to that observed in [3-3H]benzylnitrosourea ([3-3H]BzNU)-treated calf thymus DNA. However, enzymatic hydrolysates of [3-3H]BzNU-treated DNA also contained significant levels of O6-benzyl-2‘-deoxyguanosine (O6-BzdG). This radioactive adduct disappeared upon incubation of the DNA with a crude preparation of the repair protein, O6-alkylguanine−DNA alkyltransferase isolated from rat liver. These data provide evidence that O6-BzdG is probably rapidly repaired in vivo. No benzylation of esophageal mucosal DNA was detected. The level of DNA benzylation observed in tissues from [3-3H]NBzMA-treated rats was several orders of magnitude lower than the level of DNA methylation in these same tissues. Therefore, these data indicate that DNA benzylation plays a minor role, if any, in the carcinogenic activity of NBzMA.

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