title: Dose-response assessment of naphthalene-induced genotoxicity and glutathione detoxication in human TK6 lymphoblasts.
abstract: The dose-response relationship for the induction of micronuclei (MN) and the impact of glutathione (GSH) detoxication on naphthalene-induced cytotoxicity and genotoxicity were investigated in human TK6 cells. TK6 cells were exposed to 10 concentrations ranging from 0.0625 to 30μM naphthalene in the presence of β-naphthoflavone- and phenobarbital (βNP/PB)-induced rat liver S9 with a nicotinamide adenine dinucleotide phosphate-generating system. Three approaches were used to identify a no-observed-effect level (NOEL) for naphthalene-induced genotoxicity: (1) laboratory criteria of ≥ twofold increase over the concurrent solvent controls (NOEL = 10μM), (2) ANOVA with Bonferroni correction (NOEL = 2.5μM), and (3) the benchmark dose approach (BMCL(10) = 3.35μM). The NOEL and point of departure micronucleus frequency for naphthalene-induced MN are between the tested naphthalene concentrations of 2.5-10.0μM in this experimental system. Supplementation of the exposure system with physiological relevant concentrations of 5mM GSH eliminated naphthalene-induced cytotoxicity and genotoxicity; no increased cytotoxicity or genotoxicity was observed at concentrations of up to 500μM naphthalene in the presence of GSH compared with 2.5-10.0μM in the absence of GSH. Naphthalene bioactivation by βNP/PB-induced rat liver S9 exhibits a nonlinear dose-response for the induction of MN in TK6 cells with a NOEL of 2.5-10μM that in the presence of GSH is shifted upward greater than 50- to 200-fold. These data demonstrate a nonlinear dose-response for naphthalene-induced genotoxicity that is eliminated by GSH, and both observations should be considered when assessing human risk from naphthalene exposures.
authors.affiliation: Integrated Laboratory Systems, Research Triangle Park, North Carolina 27709, USA. lrecio@ils-inc.com
authors.forename: Leslie
authors.initials: L
authors.lastname: Recio
authors.forename: Kim G
authors.initials: KG
authors.lastname: Shepard
authors.forename: Lya G
authors.initials: LG
authors.lastname: Hernández
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Kedderis
mesh_terms: D000818:Animals; D001711:Biotransformation; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D008214:Lymphocytes / Q000187:drug effects* / Q000378:metabolism; D015162:Micronucleus Tests; D009153:Mutagens / Q000633:toxicity*; D009281:Naphthalenes / Q000633:toxicity*; D051381:Rats
chemical_list: D009153:Mutagens; D009281:Naphthalenes; C031721:naphthalene; D005978:Glutathione