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Long AS, Wills JW, Krolak D, Guo M, Dertinger SD, Arlt VM, White PA. Benchmark dose analyses of multiple genetic toxicity endpoints permit robust, cross-tissue comparisons of MutaMouse responses to orally delivered benzo[a]pyrene. Arch Toxicol 2018; 92:967-982. [PMID: 29177888 PMCID: PMC5818629 DOI: 10.1007/s00204-017-2099-2] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Accepted: 10/17/2017] [Indexed: 12/14/2022]
Abstract
Genetic damage is a key event in tumorigenesis, and chemically induced genotoxic effects are a human health concern. Although genetic toxicity data have historically been interpreted using a qualitative screen-and-bin approach, there is increasing interest in quantitative analysis of genetic toxicity dose-response data. We demonstrate an emerging use of the benchmark dose (BMD)-approach for empirically ranking cross-tissue sensitivity. Using a model environmental carcinogen, we quantitatively examined responses for four genetic damage endpoints over an extended dose range, and conducted cross-tissue sensitivity rankings using BMD100 values and their 90% confidence intervals (CIs). MutaMouse specimens were orally exposed to 11 doses of benzo[a]pyrene. DNA adduct frequency and lacZ mutant frequency (MF) were measured in up to 8 tissues, and Pig-a MF and micronuclei (MN) were assessed in immature (RETs) and mature red blood cells (RBCs). The cross-tissue BMD pattern for lacZ MF is similar to that observed for DNA adducts, and is consistent with an oral route-of-exposure and differences in tissue-specific metabolism and proliferation. The lacZ MF BMDs were significantly correlated with the tissue-matched adduct BMDs, demonstrating a consistent adduct conversion rate across tissues. The BMD CIs, for both the Pig-a and the MN endpoints, overlapped for RETs and RBCs, suggesting comparable utility of both cell populations for protracted exposures. Examination of endpoint-specific response maxima illustrates the difficulty of comparing BMD values for a fixed benchmark response across endpoints. Overall, the BMD-approach permitted robust comparisons of responses across tissues/endpoints, which is valuable to our mechanistic understanding of how benzo[a]pyrene induces genetic damage.
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Affiliation(s)
- Alexandra S Long
- Mechanistic Studies Division, Environmental Health Science and Research Bureau, Health Canada, 50 Colombine Driveway, Tunney's Pasture, A/L 0803A, Ottawa, ON, K1A 0K9, Canada.
- Department of Biology, University of Ottawa, Ottawa, ON, Canada.
| | - John W Wills
- Mechanistic Studies Division, Environmental Health Science and Research Bureau, Health Canada, 50 Colombine Driveway, Tunney's Pasture, A/L 0803A, Ottawa, ON, K1A 0K9, Canada
- Department of Biology, University of Ottawa, Ottawa, ON, Canada
| | - Dorothy Krolak
- Mechanistic Studies Division, Environmental Health Science and Research Bureau, Health Canada, 50 Colombine Driveway, Tunney's Pasture, A/L 0803A, Ottawa, ON, K1A 0K9, Canada
| | - Matthew Guo
- Mechanistic Studies Division, Environmental Health Science and Research Bureau, Health Canada, 50 Colombine Driveway, Tunney's Pasture, A/L 0803A, Ottawa, ON, K1A 0K9, Canada
| | | | - Volker M Arlt
- Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment and Health, King's College London, London, UK
| | - Paul A White
- Mechanistic Studies Division, Environmental Health Science and Research Bureau, Health Canada, 50 Colombine Driveway, Tunney's Pasture, A/L 0803A, Ottawa, ON, K1A 0K9, Canada
- Department of Biology, University of Ottawa, Ottawa, ON, Canada
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White PA, Douglas GR, Phillips DH, Arlt VM. Quantitative relationships between lacZ mutant frequency and DNA adduct frequency in Muta™Mouse tissues and cultured cells exposed to 3-nitrobenzanthrone. Mutagenesis 2017; 32:299-312. [PMID: 28096451 PMCID: PMC5638019 DOI: 10.1093/mutage/gew067] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Accepted: 12/13/2016] [Indexed: 02/07/2023] Open
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.
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Affiliation(s)
- Paul A White
- Environmental Health Science and Research Bureau, Health Canada, Tunney’s Pasture, Colombine Driveway, Ottawa, Ontario, Canada
| | - George R Douglas
- Environmental Health Science and Research Bureau, Health Canada, Tunney’s Pasture, Colombine Driveway, Ottawa, Ontario, Canada
| | - David H Phillips
- King’s College London, Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment and Health, Franklin-Wilkins Building, London, UK
| | - Volker M Arlt
- King’s College London, Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment and Health, Franklin-Wilkins Building, London, UK
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Wills JW, Long AS, Johnson GE, Bemis JC, Dertinger SD, Slob W, White PA. Empirical analysis of BMD metrics in genetic toxicology part II: in vivo potency comparisons to promote reductions in the use of experimental animals for genetic toxicity assessment. Mutagenesis 2016; 31:265-75. [PMID: 26984301 DOI: 10.1093/mutage/gew009] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Genotoxicity tests have traditionally been used only for hazard identification, with qualitative dichotomous groupings being used to identify compounds that have the capacity to induce mutations and/or cytogenetic alterations. However, there is an increasing interest in employing quantitative analysis of in vivo dose-response data to derive point of departure (PoD) metrics that can be used to establish human exposure limits or margins of exposure (MOEs), thereby supporting human health risk assessments and regulatory decisions. This work is an extension of our companion article on in vitro dose-response analyses and outlines how the combined benchmark dose (BMD) approach across included covariates can be used to improve the analyses and interpretation of in vivo genetic toxicity dose-response data. Using the BMD-covariate approach, we show that empirical comparisons of micronucleus frequency dose-response data across multiple studies justifies dataset merging, with subsequent analyses improving the precision of BMD estimates and permitting attendant potency ranking of seven clastogens. Similarly, empirical comparisons of Pig-a mutant phenotype frequency data collected in males and females justified dataset merging across sex. This permitted more effective scrutiny regarding the effect of post-exposure sampling time on the mutagenicity of N-ethyl-N-nitrosourea observed in reticulocytes and erythrocytes in the Pig-a assay. The BMD-covariate approach revealed tissue-specific differences in the induction of lacZ transgene mutations in Muta™Mouse specimens exposed to benzo[a]pyrene (BaP), with the results permitting the formulation of mechanistic hypotheses regarding the observed potency ranking. Lastly, we illustrate how historical dose-response data for assessments that examined numerous doses (i.e. induced lacZ mutant frequency (MF) across 10 doses of BaP) can be used to improve the precision of BMDs derived from datasets with far fewer doses (i.e. lacZ MF for 3 doses of dibenz[a,h]anthracene). Collectively, the presented examples illustrate how innovative use of the BMD approach can permit refinement of the use of in vivo data; improving the efficacy of experimental animal use in genetic toxicology without sacrificing PoD precision.
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Affiliation(s)
- John W Wills
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, Ontario K1A 0K9, Canada,
| | - Alexandra S Long
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, Ontario K1A 0K9, Canada
| | - George E Johnson
- Swansea University Medical School, Institute of Life Science, Swansea SA2 8PP, UK
| | | | | | - Wout Slob
- National Institute for Public Health and the Environment (RIVM), 3720 BA Bilthoven, The Netherlands
| | - Paul A White
- Environmental Health Science and Research Bureau, Health Canada, Ottawa, Ontario K1A 0K9, Canada,
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Ypsilantis P, Tentes L, Assimakopoulos SF, Kortsaris A, Scopa CD, Pitiakoudis M, Simopoulos C. Dose related effects of ifosfamide on enterocyte apoptosis in different sites of the rabbit intestine. Toxicology 2004; 200:135-43. [PMID: 15212810 DOI: 10.1016/j.tox.2004.03.020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2003] [Revised: 02/02/2004] [Accepted: 03/19/2004] [Indexed: 11/20/2022]
Abstract
OBJECTIVE We investigated the potential dose related apoptotic effect of subchronic administration of the alkylating chemotherapeutic agent ifosfamide in different sites of the small and large rabbit intestine. MATERIALS AND METHODS Twenty New Zealand White rabbits received intravenously every week, for 10 weeks, 0 (group S, controls, n = 5), 30 (group A, n = 5), 45 (group B, n = 5) or 60 mg/kg ifosfamide (group C, n = 5). One day after the end of the treatment period, segments of jejunum, ileum, cecum, proximal and distal colon were excised. Intestinal mucosa apoptosis was detected by agarose gel electrophoresis and quantified by DNA fragmentation and standard terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP)-biotin nick-end labelling (TUNEL) assays by which the percentage of fragmented DNA and the ratio of apoptotic cells per crypt (apoptotic index) were determined, respectively. RESULTS At low dose (group A), ifosfamide had minor apoptotic effect on enterocytes, which was enhanced mainly in the small intestine when the dose was increased (group B); at the highest dose tested (group C), this effect was extended to the large intestine. In all groups of animals, the observed crypt cell apoptosis was maximal in the ileum, while minimal in the proximal colon. CONCLUSIONS Our results show a dose and intestinal site-dependent induction of enterocyte apoptosis after subchronic ifosfamide administration in the rabbit.
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Affiliation(s)
- Petros Ypsilantis
- Laboratory of Experimental Surgery, Medical School, Democritus University of Thrace, 68100 Alexandroupolis, Greece.
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