title: A retrospective evaluation method for in vitro mammalian genotoxicity tests using cytotoxicity index transformation formulae.
abstract: Although in vitro chromosomal aberration tests and micronucleus tests have been widely used for genotoxicity evaluation, false-positive results have been reported under strong cytotoxic conditions. To reduce false-positive results, the new Organization for Economic Co-operation and Development (OECD) test guideline (TG) recommends the use of a new cytotoxicity index, relative increase in cell count or relative population doubling (RICC/RPD), instead of the traditionally used index, relative cell count (RCC). Although the use of the RICC/RPD may result in different outcomes and require re-evaluation of tested substances, it is impractical to re-evaluate all existing data. Therefore, we established a method to estimate test results from existing RCC data. First, we developed formulae to estimate RICC/RPD from RCC without cell counts by considering cell doubling time and experiment time. Next, the accuracy of the cytotoxicity index transformation formulae was verified by comparing estimated RICC/RPD and measured RICC/RPD for 3 major chemicals associated with false-positive genotoxicity test results: ethyl acrylate, eugenol and p-nitrophenol. Moreover, 25 compounds with false-positive in vitro chromosomal aberration (CA) test results were re-evaluated to establish a retrospective evaluation method based on derived estimated RICC/RPD values. The estimated RICC/RPD values were in good agreement with the measured RICC/RPD values for every concentration and chemical, and the estimated RICC suggested the possibility that 12 chemicals (48%) with previously judged false-positive results in fact had negative results. Our method enables transformation of RCC data into RICC/RPD values with a high degree of accuracy and will facilitate comprehensive retrospective evaluation of test results.
authors.affiliation: R&D Safety Science Research, Kao Corporation, 2606 Akabane, Ichikai-Machi, Haga-Gun, Tochigi 321-3497, Japan.
authors.forename: Yurika
authors.initials: Y
authors.lastname: Fujita
authors.affiliation: R&D Safety Science Research, Kao Corporation, 2606 Akabane, Ichikai-Machi, Haga-Gun, Tochigi 321-3497, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Kasamatsu
authors.affiliation: R&D Safety Science Research, Kao Corporation, 2606 Akabane, Ichikai-Machi, Haga-Gun, Tochigi 321-3497, Japan.
authors.forename: Naohiro
authors.initials: N
authors.lastname: Ikeda
authors.affiliation: R&D Safety Science Research, Kao Corporation, 2606 Akabane, Ichikai-Machi, Haga-Gun, Tochigi 321-3497, Japan.
authors.forename: Naohiro
authors.initials: N
authors.lastname: Nishiyama
authors.affiliation: R&D Safety Science Research, Kao Corporation, 2606 Akabane, Ichikai-Machi, Haga-Gun, Tochigi 321-3497, Japan. Electronic address: honda.hiroshi@kao.co.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Honda
mesh_terms: D000179:Acrylates / Q000633:toxicity; D000818:Animals; D002452:Cell Count; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002869:Chromosome Aberrations / Q000139:chemically induced; D004249:DNA Damage; D005054:Eugenol / Q000633:toxicity; D017408:Guidelines as Topic; D006801:Humans; D008322:Mammals; D015162:Micronucleus Tests / Q000379:methods; D009152:Mutagenicity Tests / Q000379:methods* / Q000592:standards; D009596:Nitrophenols / Q000633:toxicity; D012189:Retrospective Studies
chemical_list: D000179:Acrylates; D009596:Nitrophenols; D005054:Eugenol; C040833:ethyl acrylate; C024836:4-nitrophenol
keywords: Chromosomal aberration test; Cytotoxicity; False positive; Genotoxicity; Micronucleus test