A comparison of transgenic rodent mutation and in vivo comet assay responses for 91 chemicals

David Kirkland ,Frank Le Curieux ,Marilyn J Aardema ,Alexandra S Long ,George E Johnson ,Kristine L Witt ,Matthew J Lebaron ,Patricia Escobar ,Andrew Williams ,Mirjam Luijten ,Rohan Kulkarni ,Carol Beevers ,Daniel J Roberts ,David P Lovell ,Francesco Marchetti ,John Nicolette ,Javed A Bhalli ,Dan D Levy ,Stefan Pfuhler ,Christopher S Farabaugh ,Véronique Thybaud ,Leon F Stankowski ,Sandy Weiner ,Melanie Guérard ,George R Douglas ,Jasmin Lott ,Robert R Young

doi:10.1016/j.mrgentox.2019.01.007

Abstract

A database of 91 chemicals with published data from both transgenic rodent mutation (TGR) and rodent comet assays has been compiled. The objective was to compare the sensitivity of the two assays for detecting genotoxicity. Critical aspects of study design and results were tabulated for each dataset. There were fewer datasets from rats than mice, particularly for the TGR assay, and therefore, results from both species were combined for further analysis. TGR and comet responses were compared in liver and bone marrow (the most commonly studied tissues), and in stomach and colon evaluated either separately or in combination with other GI tract segments. Overall positive, negative, or equivocal test results were assessed for each chemical across the tissues examined in the TGR and comet assays using two approaches: 1) overall calls based on weight of evidence (WoE) and expert judgement, and 2) curation of the data based on a priori acceptability criteria prior to deriving final tissue specific calls. Since the database contains a high prevalence of positive results, overall agreement between the assays was determined using statistics adjusted for prevalence (using AC1 and PABAK). These coefficients showed fair or moderate to good agreement for liver and the GI tract (predominantly stomach and colon data) using WoE, reduced agreement for stomach and colon evaluated separately using data curation, and poor or no agreement for bone marrow using both the WoE and data curation approaches. Confidence in these results is higher for liver than for the other tissues, for which there were less data. Our analysis finds that comet and TGR generally identify the same compounds (mainly potent mutagens) as genotoxic in liver, stomach and colon, but not in bone marrow. However, the current database content precluded drawing assay concordance conclusions for weak mutagens and non-DNA reactive chemicals.

Highlights

In the early decades of regulatory genotoxicity testing, the most commonly used in vivo somatic cell tests supported by the Organisation for Economic Co-operation and Development (OECD) guidelines only examined effects in bone marrow, namely induction of chromosomal aberrations (CA; OECD Test Guideline [TG] 475, [1]) or micronuclei (MN; OECD TG 474 [2])
A key question the working group wished to address was whether it is necessary to follow up a chemical that has been shown to be mutagenic in vitro with an in vivo gene mutation assay (TGR test), or whether it might be acceptable to conduct an in vivo comet assay
One experienced individual reviewed all of the collected data and allocated overall calls based on weight of evidence (WoE) and expert judgement

Summary

Introduction

In the early decades of regulatory genotoxicity testing, the most commonly used in vivo somatic cell tests supported by the Organisation for Economic Co-operation and Development (OECD) guidelines only examined effects in bone marrow, namely induction of chromosomal aberrations (CA; OECD Test Guideline [TG] 475, [1]) or micronuclei (MN; OECD TG 474 [2]). The development of the TGR OECD guideline was supported by the publication of Lambert et al [8] and the OECD Detailed Review Paper [9], and for the comet assay by a collaborative multi-laboratory validation trial (see [10,11]). Both assays have their strengths and limitations:

Methods

Results

Conclusion