title: Assessment of mechanisms driving non-linear dose-response relationships in genotoxicity testing.
abstract: In genetic toxicology, risk assessment has traditionally adopted linear dose-responses for any compound that causes genotoxic effects. Increasing evidence of non-linear dose-responses, however, suggests potential cellular tolerance to low levels of many genotoxicants with diverse modes of action. Such putative non-linear dose-responses need to be substantiated by strong mechanistic data that identifies the mechanisms responsible for the tolerance to low doses. This can be achieved by experimental demonstration of cytoprotective mechanisms and by providing experimental support for the existence of tolerance mechanisms against low dose effects. By highlighting key experiments into low dose mechanisms, this review aims to clarify which mechanistic data are required to support the use of non-linear dose-response models in risk assessment. Such key experiments are presented and discussed for alkylating agents, oxidants, particulate matter, nucleoside analogues, topoisomerase inhibitors and aneugens and exemplify the use of gene knockout models or transgenic models as well as chemical modulators of key effectors of relevant pathways and their impact on dose-response relationships. In vitro studies are particularly valuable to elucidate mechanisms of low-dose protection or lack thereof, while in vivo experiments are most appropriate for deriving a safe dose. In order to evaluate the existence of non-linear dose-response relationships for genotoxicants, we suggest that careful attention should be given to the mode of genotoxic action, relevant biomarkers of exposure, as well as to the existence and impact of potential cytoprotective mechanisms like detoxifying metabolism and DNA repair.
authors: F. Hoffmann La Roche Ltd., Pharmaceutical Research and Early Development, Pharmaceutical Science, Innovation Center Basel, Basel, Switzerland. Electronic address: melanie.guerard@roche.com.
authors: M
authors: M
authors: Guérard
authors: BASF SE Ludwigshafen, Ludwigshafen, Germany.
authors: M
authors: M
authors: Baum
authors: Fraunhofer Institute for Toxicology and Experimental Medicine ITEM, Hannover, Germany.
authors: A
authors: A
authors: Bitsch
authors: Department of Chemistry, Division of Food Chemistry and Toxicology, University of Kaiserslautern, Kaiserslautern, Germany.
authors: G
authors: G
authors: Eisenbrand
authors: Novartis Institutes for BioMedical Research, Preclinical Safety, Basel, Switzerland.
authors: A
authors: A
authors: Elhajouji
authors: Institute of Pharmacy and Biochemistry, University of Mainz, Mainz, Germany.
authors: B
authors: B
authors: Epe
authors: Department of Chemistry, Division of Food Chemistry and Toxicology, University of Kaiserslautern, Kaiserslautern, Germany.
authors: M
authors: M
authors: Habermeyer
authors: Institute of Toxicology, University Medical Center, Mainz, Germany.
authors: B
authors: B
authors: Kaina
authors: Novartis Institutes for BioMedical Research, Preclinical Safety, Basel, Switzerland.
authors: H J
authors: HJ
authors: Martus
authors: The Procter & Gamble Company, Global Product Stewardship, Human Safety, Mason, OH, USA.
authors: S
authors: S
authors: Pfuhler
authors: DLAC Dienstleistungsagentur Chemie GmbH, Braunschweig, Germany.
authors: C
authors: C
authors: Schmitz
authors: Bayer HealthCare, Investigational Toxicology, Berlin, Germany.
authors: A
authors: A
authors: Sutter
authors: Institute of Toxicology, University Medical Center, Mainz, Germany.
authors: A D
authors: AD
authors: Thomas
authors: Fraunhofer Institute for Toxicology and Experimental Medicine ITEM, Hannover, Germany.
authors: C
authors: C
authors: Ziemann
authors: Ferderal Institute for Drugs and Medical Devises-Bundesinstitut für Arzneimittel und Medizinprodukte (BfArM), Genetic and Reproductive Toxicology, Bonn, Germany.
authors: R
authors: R
authors: Froetschl
mesh_terms: D000477:Alkylating Agents / Q000633:toxicity; D024422:Aneugens / Q000009:adverse effects; D000818:Animals; D004249:DNA Damage; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008956:Models, Chemical; D009152:Mutagenicity Tests / Q000379:methods*; D009153:Mutagens / Q000009:adverse effects*; D009705:Nucleosides / Q000009:adverse effects; D016877:Oxidants / Q000009:adverse effects; D052638:Particulate Matter / Q000009:adverse effects; D018570:Risk Assessment; D059003:Topoisomerase Inhibitors / Q000009:adverse effects
chemical_list: D000477:Alkylating Agents; D024422:Aneugens; D009153:Mutagens; D009705:Nucleosides; D016877:Oxidants; D052638:Particulate Matter; D059003:Topoisomerase Inhibitors
keywords: DNA damage; Genetic toxicology; Non-linear dose–response; Threshold