32 P Analysis of DNA Adducts in Tissues of Benzene-Treated Rats

Abstract

Solid tumors have been reported in the Zymbal gland, oral and nasal cavities, liver, and mammary gland of Sprague-Dawley rats following chronic, high-dose administration of benzene. The carcinogenic activity of benzene is thought to be caused by activation to toxic metabolites that can interact with DNA, forming covalent adducts. A nuclease Pi-enhanced 32P-postlabeling assay, having a sensitivity limit of 1 adduct in 109-10 DNA nucleotides, was found suitable for measuring aromatic DNA adducts derived in vitro from catechol, benzenetriol (BT), phenol, hydroquinone (HQ), and benzoquinone (BQ), potential metabolites of benzene. When DNA specimens isolated from tissues of female SpraguewDawley rats at 24 hr after an oral gavage dose of 200 to 500 mg/kg, 5 days/week, in olive oil (3 mL/kg) for 1 day, 1 week, 5 weeks, and 10 weeks were analyzed by the 32P-postlabeling procedure, no aromatic adducts were detected unequivocally with DNA samples of liver, kidney, bone marrow, and mammary gland. With Zymbal gland DNA, three weak spots at levels totaling four lesions per 109 DNA nucleotides were seen only after 10 weeks of treatment, and these adducts did not correspond chromatographically to major adducts in vitro from the above specified compounds. Consequently, this finding requires confirmatory experiments. This distinct adduct pattern may relate to tumor induction in this organ following benzene administration. Our results also indicate that DNA adducts derived from catechol, BT, phenol, HQ, and BQ are either not formed in vivo with benzene or formed at levels below the detection limit of 1 adduct per 10910 DNA nucleotides.

Nasal Cytotoxic and Carcinogenic Activities of Systemically Distributed Organic Chemicals

“…Benzene yielded mixed results in genotoxicity test systems (International Agency for Research on Cancer, 2000b), with the exception of bone marrow. DNA binding was either absent or extremely low in several tissues in rats (Reddy et al, 1989), although binding was reported under extreme conditions (twice-daily treatment for 1 to 7 days with 440 mg/kg benzene) (Bodell et al, 1996). A scheme for the biotransformation of benzene based upon (Snyder and Hedli, 1996) is shown in Figure 19.…”

Detection of PCB Adducts by the 32P-Postlabeling Technique

“…The toxicity of benzene is most likely due to the oxidation of its dihydroxy metabolites, i.e., catechol and p-hydroquinone, to semiquinones and quinones (27,28). In rats, benzene adducts were not detected in the DNA isolated from liver, kidney, bone marrow, or mammary gland, but three minor adducts were detected in Zymbal gland DNA (29), which is the primary target tissue for benzene in rats (30). In mice, radioactively labeled benzene was covalently bound to macromolecules in liver, bone marrow, kidney, lung, spleen, blood, and muscle (31).…”