DNA adduct formation and T lymphocyte mutation induction in F344 rats implanted with tumorigenic doses of 1,6-dinitropyrene.
Diesel emissions are known to induce tumors in laboratory animals and are suspected of being carcinogenic in humans. Of the compounds associated with diesel exhaust, 1,6-dinitropyrene is a particularly potent mutagen and carcinogen; thus, monitoring the toxic effects of 1,6-dinitropyrene may provide a means for assessing the carcinogenic risk associated with exposure to diesel emissions. In these experiments, 1,6-dinitropyrene was implanted into the lungs of rats according to a protocol known to induce lung tumors; the DNA adducts were characterized and quantified in target (lung) and surrogate (liver, white blood cells, and spleen lymphocytes) tissues. In addition, mutation induction was assayed at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus in spleen T lymphocytes, and the relation between adduct concentration and mutation induction was elucidated. Rats were administered 30 micrograms or 100 micrograms of [ring-3H]1,6-dinitropyrene and adduct levels were quantified for up to one month after treatment. In lung tissue, white blood cells, liver tissue, and spleen lymphocytes, one major DNA adduct, N-(deoxyguanosin-8-yl)-1-amino-6-nitropyrene, was detected. In each tissue, the levels of this adduct reached a maximal level one to seven days after treatment and decreased to approximately 25% of the peak values by 28 days after treatment. DNA adduct formation in the lung was approximately tenfold higher than that observed in the other tissues. A dose-response relation was not observed in the lung, white blood cells, or liver; but in the spleen lymphocytes, a threefold increase in dose resulted in approximately a twofold increase in adduct formation. After a similar treatment with 1,6-dinitropyrene, mutations were assayed at the hprt locus in spleen T lymphocytes for up to 51 weeks. Compared with control animals treated with solvent, 1,6-dinitropyrene induced a significant increase in mutant frequency with the 100-microgram dose, typically producing twofold more mutants than the 30-microgram dose. With both doses, the mutant frequency increased until 21 weeks after treatment with 1,6-dinitropyrene, remained constant until week 40, and then began to decrease. Nonetheless, nearly one year after treatment, the mutant frequency in rats treated with 1,6-dinitropyrene was greater than that observed in control rats. In a subsequent experiment, rats were administered 0, 0.3, 1, 3, 10, 30, 100, or 150 micrograms of 1,6-dinitropyrene and the extent of adduct formation was determined seven days after treatment. In the lung nuclei, liver nuclei, and spleen lymphocyte DNA, a significant dose-response relation was observed, with the extent of adduct formation increasing significantly at a dose of 10 micrograms. A twofold increase in dose resulted in a twofold increase in adduct formation up to the 30-microgram dose in lung nuclei DNA, and up to the 10-microgram dose in liver nuclei DNA. At higher doses, the extent of adduct formation still increased but the rate of increase was much lower than that occurring at lower doses. To assess the mutation frequency as a function of dose, additional rats were treated with 0, 0.3, 1, 3, 10, 30, 100, or 150 micrograms of 1,6-dinitropyrene and mutations were assayed at the hprt locus in spleen T lymphocytes 21 weeks after treatment. In this experiment, a significant dose-response relation was observed, with the increase in mutants becoming significant at 1 microgram and higher doses of 1,6-dinitropyrene. These data indicate that 1,6-dinitropyrene, a constituent of diesel emissions, is metabolically activated by nitroreduction to produce DNA adducts in target and surrogate tissues. They further suggest that T lymphocyte mutations may be a more sensitive and longer-lived biomarker than DNA adducts for assessing previous exposures to genotoxic agents, such as nitro-polynuclear aromatic hydrocarbons.
Beland
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Division of Biochemical Toxicology, National Center for Toxicological Research, HFT-100, Jefferson, AR 72079, USA.
D000818:Animals; D002467:Cell Nucleus / Q000187:drug effects / Q000235:genetics; D018736:DNA Adducts / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D004343:Drug Implants; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D007041:Hypoxanthine Phosphoribosyltransferase / Q000187:drug effects / Q000235:genetics; D008168:Lung / Q000187:drug effects / Q000378:metabolism; D008297:Male; D016296:Mutagenesis / Q000187:drug effects*; D009153:Mutagens / Q000378:metabolism / Q000633:toxicity*; D011721:Pyrenes / Q000378:metabolism / Q000633:toxicity*; D051381:Rats; D011916:Rats, Inbred F344; D013154:Spleen / Q000166:cytology / Q000187:drug effects; D013601:T-Lymphocytes / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors; D014018:Tissue Distribution; D001335:Vehicle Emissions / Q000633:toxicity
D018736:DNA Adducts; D004343:Drug Implants; D009153:Mutagens; D011721:Pyrenes; D001335:Vehicle Emissions; C033309:1,6-dinitropyrene; D007041:Hypoxanthine Phosphoribosyltransferase