Combination effects of nano-TiO2 and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on biotransformation gene expression in the liver of European sea bass Dicentrarchus labrax

The aim of present study was to investigate the influence of titanium dioxide nanoparticles (nano-TiO2, Aeroxide® P25) on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) dependent biotransformation gene expression in liver of juvenile European sea bass Dicentrarchus labrax. An in vivo 7 day waterborne exposure was performed with nano-TiO2 (1 mg/L) and 2,3,7,8-TCDD (46 pg/L), singly and in combination. The mRNA expression of aryl hydrocarbon receptor repressor (Ahrr), estrogen receptor (erβ2), ABC transport proteins as Abcb1, Abcc1-c2-g2, cytochrome P450 (cyp1a), glutathione-s-transferase (gsta), glutathione reductase (gr) and engulfment and motility (ELMO) domain-containing protein 2 (elmod2) was investigated. Ahrr, erβ2, abcc1 and abcg2 resulted down-regulated with respect to controls in all experimental groups. Co-exposure to nano-TiO2 and 2,3,7,8- TCDD caused a further significant down regulation of ahrr, erβ2, Abcb1 and Abcc2 compared to single chemical exposure (nano-TiO2 or 2,3,7,8-TCDD alone). No effects were observed for 2,3,7,8-TCDD and nano-TiO2 alone in abcb1 gene, while abcc2 was down-regulated by nano-TiO2 alone. Cyp1a, gst and elmod2 genes were upregulated by 2,3,7,8-TCDD and to a similar extent after co-exposure. Overall the results indicate that nano-TiO2 is unlikely to interfere with 2,3,7,8-TCDD-dependent biotransformation gene expression in the liver of European sea bass, although the effects of co-exposure observed in ABC transport mRNAs might suggest an impact on xenobiotic metabolite disposition and transport in European sea bass liver.