Toxicology Letters 126 (2002) 61 – 68 DNA damage and repair in human leukocytes exposed to styrene-7,8-oxide measured by the comet assay Blanca Laffon a,b , Eduardo Pa ´saro b , Josefina Me ´ndez a, * a Dept. de Biologia Celular y Molecular, Facultad de Ciencias, Uniersidade da Corun ˜a, Campus A Zapateira s /n, 15071 La Corun ˜a, Spain b Instituto de Ciencias de la Salud, Uniersidade da Corun ˜a, La Corun ˜a, Spain Received 25 May 2001; received in revised form 20 August 2001; accepted 29 August 2001 Abstract Styrene-7,8-oxide (SO) is produced by cytochrome p450 monooxygenases as the main mammalian metabolite of styrene, an important industrial chemical present at high concentrations in the ambient air of fiberglass-reinforced plastic plants. Previous studies have shown positive results for SO in the induction of several cytogenetic endpoints in vitro. In this work we have evaluated, by means of the comet assay, the potential of SO to act as a DNA damaging agent in human peripheral leukocytes and the ability of white blood cells to repair the DNA damage induced by this compound. Our results show that SO induces DNA damage at concentrations higher than 50 M in a dose-dependent manner, and that the lesions produced by SO are efficiently removed within a few hours after the end of treatment. © 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Styrene-7,8-oxide; Comet assay; Human leukocytes; DNA repair www.elsevier.com/locate/toxlet 1. Introduction Styrene-7,8-oxide (SO) is the primary mam- malian metabolite of styrene, an organic solvent widely used in the production of plastics, resins, insulators and synthetic rubber. The highest hu- man exposure to styrene takes place in fiberglass- reinforced plastic plants, where the compound is inhaled during by-hand-lamination procedures (Miller et al., 1994). In such factories, SO is produced from airborne styrene in the presence of air and light and also when peroxides are added to the resin as polymerisation-reaction initiators. The concentration of SO in the air at the work place has been calculated to be 1/1000 of the concurrent air concentration of styrene (Pfa ¨ffli and Sa ¨a ¨ma ¨nen, 1993). In vivo, styrene is metabolised to SO by cy- tochrome P450 monooxygenases, the isoforms CYP2B6 and CYP2E1 (present in human liver and lung) and CYP2F1 (present in human lung) being the most effective in the transformation (Nakajima et al., 1994; Kim et al., 1997). Previous studies performed in several mammalian cell sys- tems and lower eukaryotes treated in vitro with * Corresponding author. Tel.: +34-981-167000; fax: +34- 981-167065. E-mail address: fina@udc.es (J. Me ´ndez). 0378-4274/02/$ - see front matter © 2002 Elsevier Science Ireland Ltd. All rights reserved. PII:S0378-4274(01)00432-5