Titanium dioxide nanoparticles modulate the toxicological response to cadmium in the gills of Mytilus galloprovincialis

We investigated the influence of titanium dioxide nanoparticles (nano-TiO<inf>2</inf>) on the response to cadmium in the gills of the marine mussel Mytilus galloprovincialis in terms of accumulation and toxicity. Mussels were in vivo exposed to nano-TiO<inf>2</inf>, CdCl<inf>2</inf>, alone and in combination. Several cellular biomarkers were investigated in gills: ABC transport proteins and metallothioneins at gene/protein (abcb1, abcc-like and mt-20) and functional level, GST activity, NO production and DNA damage (Comet assay). Accumulation of total Cd and titanium in gills as in whole soft tissue was also investigated. Significant responses to Cd exposure were observed in mussel gills as up-regulation of abcb1 and mt-20 gene transcription, increases in total MT content, P-gp efflux and GST activity, DNA damage and NO production. Nano-TiO<inf>2</inf> alone increased P-gp efflux activity and NO production. When combined with Cd, nano-TiO<inf>2</inf> reduced the metal-induced effects by significantly lowering abcb1 gene transcription, GST activity, and DNA damage, whereas, additive effects were observed on NO production. A lower concentration of Cd was observed in the gills upon co-exposure, whereas, Ti levels were unaffected. A competitive effect in uptake/accumulation of nano-TiO<inf>2</inf> and Cd seems to occur in gills. A confirmation is given by the observed absence of adsorption of Cd onto nano-TiO<inf>2</inf> in sea water media.