Naphthalene toxicity in mice and aryl hydrocarbon receptor-mediated CYPs

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Abstract

Naphthalene (NP) has been designated a ‘reasonably anticipated human carcinogen’ because of positive responses in carcinogenicity bioassays in rodents. Whereas CYP2F enzymes are widely regarded as responsible for NP bioactivation, other metabolic enzymes—including CYP1A1 and CYP1A2—produce NP-1,2-oxide in vitro. We investigated the role of these aryl hydrocarbon receptor (AHR)-mediated enzymes in NP toxicity in two ways. First, NP was assessed for the ability to activate transcription via the AHR in an in vitro luciferase reporter assay and was found to have no activity. Second, mice deficient in AHR, CYP1A1 or CYP1A2 were dosed with NP alone, or following pretreatment with the CYP2F inhibitor 5-phenyl-1-pentyne. None of the knockout mice were protected from olfactory toxicity of NP. In contrast, CYP1A1- and CYP1A2-null mice pretreated with 5-phenyl-1-pentyne exhibited no NP olfactory toxicity. These results suggest that AHR-mediated enzymes do not contribute significantly to NP bioactivation in the intact animal.

Section snippets

Methods

Chemicals. Naphthalene and dimethyl sulfoxide were obtained from Fisher Scientific; 5-phenyl-1-pentyne was purchased from GFS (Columbus OH); TCDD was purchased from Accustandard, Inc. (New Haven, CT).

Mice. Ahr−/−, Cyp1a1−/−, and Cyp1a2−/− knockout mice were generated from in-house breeding colonies, and wild-type littermates were used as controls. Generation of the respective knockout mouse lines has been previously described [25], [26], [27], and these mice are maintained on the C57BL/6J

Knockout mouse studies

Wild-type, Cyp1a1−/−, and Cyp1a2−/− mice treated with 5-phenyl-1-pentyne + NP showed no overt sign of toxicity 18 h after treatment and were completely protected from the olfactory toxicity of NP. In contrast, the non-pretreated NP-treated wild-type, Cyp1a1−/−, and Cyp1a2−/− mice showed labored breathing and hemorrhagic lungs upon sacrifice, as well as nearly 100% sloughing of the olfactory mucosa (Fig. 1). Ahr−/− mice were similarly not protected from NP-induced olfactory mucosal degeneration and

Discussion

The results of our in vivo NP treatment studies revealed that mice in which the Ahr gene is ablated are not protected from NP cytotoxicity. We also investigated the impact of the absence of the Cyp1a1 and Cyp1a2 genes on susceptibility to NP-induced respiratory tract damage, given that both genes are inducible in lung, and the expressed proteins have been shown to convert NP to NP-1,2-oxide in vitro[15], [16], [31]. NP did not stimulate gene transcription via the AHR in our study, suggesting

Acknowledgments

This work was supported by NIH Grants R01 ES08147 (D.W.N.) and P30 ES06096 (M.B.G., D.W.N., A.P., and T.P.D.).

References (34)

  • J.N. McDougal et al.

    Assessment of skin absorption and penetration of JP-8 jet fuel and its components

    Toxicol. Sci.

    (2000)
  • United States Environmental Protection Agency (2000). Health and Environmental Effects Profile for Naphthalene. U.S....
  • ATSDR, ToxFAQs™ for naphthalene, 1-methylnaphthalene, and 2-methylnaphthalene, http://www.atsdr.cdc.gov/tfacts67.html...
  • E.J. Molloy et al.

    Perinatal toxicity of domestic naphthalene exposure

    J. Perinatol.

    (2004)
  • M. Kaplan et al.

    Severe hemolysis and hyperbilirubinemia due to perinatal naphthalene exposure

    J. Perinatol.

    (2005)
  • National Toxicology Program (1992). Toxicology and carcinogenesis studies of naphthalene (CAS No. 91-20-3) in B6C3F1...
  • National Toxicology Program (2000). Toxicology and carcinogenesis studies of naphthalene (CAS No. 91-20-3) in F344/N...
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