Quantitative relationships between lacZ mutant frequency and DNA adduct frequency in Muta™Mouse tissues and cultured cells exposed to 3-nitrobenzanthrone.

Paul A White,David H Phillips,George R Douglas,Volker M Arlt

doi:10.1093/mutage/gew067

Paul A White, David H Phillips + Show 2 more

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https://doi.org/10.1093/mutage/gew067

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Journal: Mutagenesis	Publication Date: Jan 16, 2017
Citations: 12	License type: cc-by

Affiliation: King's College London, Health Canada

Abstract

The frequency of stable DNA adducts in a target tissue can be used to assess biologically effective dose; however, the utility of the metric in a risk assessment context depends on the likelihood that the DNA damage will be manifested as mutation. Previously, we employed the Muta™Mouse system to examine the induction of lacZ mutants and DNA adducts following exposure to the well-studied mutagenic carcinogen 3-nitrobenzanthrone (3-NBA). In this follow-up work, we examined the empirical relationships between total adduct frequency and mutant frequency (MF) in tissues and cultured cells following acute 3-NBA exposure. The results show a significant induction of DNA damage and lacZ mutants in liver, colon and bone marrow, as well as FE1 pulmonary epithelial cells. In contrast, lung and small intestine samples had low, but significantly elevated adduct levels, with no significant increases in lacZ MF. Additional analyses showed a significant relationship between the mutagenic efficiency of total adducts, measured as the slope of the relationships between MF and total adduct frequency, and tissue-specific mitotic index (MI). The lack of mutation response in lung, in contrast to the high in vitro MF in FE-1 lung cells, is likely related to the 100-fold difference in MI. The lack of small intestine mutagenic response may be related to limited metabolic capacity, differences in DNA repair, and /or chemically induced apoptosis that has been observed for other potent mutagens. The results indicate that interpretation of adduct frequency values in a risk assessment context can be improved by considering the MI of the target tissue; however, more generalised interpretation is hampered by tissue-specific variations in metabolic capacity and damage processing. The work provides a proof of principle regarding the use of the Muta™Mouse system to critically examine the health risks associated with tissue-specific adduct loads.

Highlights

Chemical modifications of nucleotides are a major cause of DNA damage and mutation; publications documenting the reaction of chemical mutagens with DNA date back to the late 1940s when Elmore et al [1] showed that mustard gas, bis(2-chloroethyl)sulfide, reacts with DNA in vitro
In this follow-up work, we examined the empirical relationships between total adduct frequency and mutant frequency (MF) in tissues and cultured cells following acute 3-NBA exposure.The results show a significant induction of DNA damage and lacZ mutants in liver, colon and bone marrow, as well as FE1 pulmonary epithelial cells
We documented the formation of stable DNA adducts and lacZ transgene mutations in MutaTMMouse in vivo and MutaTMMouse cells in vitro following different exposures to 3-NBA [37]. In this communication we examine the empirical relationships between total adduct frequency and total MF in MutaTMMouse tissues and cultured MutaTMMouse cells exposed to 3-NBA

Summary

Introduction

Chemical modifications of nucleotides are a major cause of DNA damage and mutation; publications documenting the reaction of chemical mutagens with DNA date back to the late 1940s when Elmore et al [1] showed that mustard gas, bis(2-chloroethyl)sulfide, reacts with DNA in vitro. In an in vivo context, the observed frequency of DNA adducts in a given tissue can be employed as a marker of internal dose and target tissue exposure (i.e., biologically effective dose). It has become increasingly clear that the frequency of stable, promutagenic DNA adducts in a target tissue may have a role in facilitating risk assessment of mutagenic carcinogens in environmental and occupational settings and, as such, DNA adduct analysis has become an essential tool in molecular epidemiology [5,6]. Since regulatory decisions are based on mutagenic activity and induced mutation frequency (MF), rather than DNA damage and adduct frequency, there is ongoing debate regarding the utility of adduct frequency metrics in a health and disease risk context. The context for the use of DNA adducts in assessing disease risk has been addressed in several excellent reviews [7,9,10,11,12,13,14,15,16]

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