title: Lack of DNA damage induction by okadaic acid, a marine toxin, in the CHO-Hprt and the in vitro UDS assays.
abstract: Okadaic acid (OA) is a marine toxin produced by dinoflagellates and responsible for human intoxications. OA is a specific inhibitor of serine/threonine protein phosphatases PP1 and PP2A and a potent tumor promoter in mouse skin and rat glandular stomach. In a previous study, we demonstrated that OA induced aneuploidy in CHO-K1 cells using the cytokinesis-block micronucleus (CBMN) assay coupled to FISH and concluded that OA was not a direct mutagen. As some previous in vitro mutagenicity studies had given positive results with OA, we decided to perform two additional in vitro mutagenicity assays in accordance with the OECD guidelines: (i) the CHO/Hprt test, which provides end points about locus-specific gene mutation; (ii) the in vitro unscheduled DNA synthesis (UDS) assay in rat hepatocytes, which measures [(3)H]thymidine incorporation into DNA undergoing excision repair. In the CHO/Hprt assay, there was no significant increase in the number of mutants for doses ranging from 5 to 5000 nM in the presence or absence of rat liver S9 fraction. In the in vitro UDS assay, OA did not induce primary DNA damages in rat hepatocytes following 18 h exposure at concentrations between 1.32 and 100 nM. As OA could affect the DNA repair systems via the inhibition of protein phosphatases, its effects on the repair kinetic of 2AAF-induced DNA damage were also investigated with the UDS assay. The results showed that OA did not interact with the DNA-repair process involved in in vitro UDS in rat hepatocytes. We concluded that OA failed to induce direct DNA damage but acted principally by altering the chromosome number, which could contribute to its carcinogenic effect.
authors.affiliation: AFSSA, Laboratoire d'Etudes et de Recherches sur les Médicaments Vétérinaires et les Désinfectants, Unité de Toxicologie Alimentaire, B.P. 90203, 35302 Fougères Cedex, France.
authors.forename: Ludovic
authors.initials: L
authors.lastname: Le Hégarat
authors.forename: Fabrice
authors.initials: F
authors.lastname: Nesslany
authors.forename: Annick
authors.initials: A
authors.lastname: Mourot
authors.forename: Daniel
authors.initials: D
authors.lastname: Marzin
authors.forename: Valérie
authors.initials: V
authors.lastname: Fessard
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects*; D004261:DNA Replication / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D022781:Hepatocytes; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D008387:Marine Toxins / Q000633:toxicity*; D009152:Mutagenicity Tests; D019319:Okadaic Acid / Q000633:toxicity*; D051381:Rats; D013997:Time Factors; D014316:Tritium
chemical_list: D008387:Marine Toxins; D014316:Tritium; D019319:Okadaic Acid; D007041:Hypoxanthine Phosphoribosyltransferase