Histopathological indices and inflammatory response in the digestive gland of the mussel Mytilus galloprovincialis as biomarker of immunotoxicity to silver nanoparticles

Background: Histopathological assessments approaches in bivalves have become an important tool in environmental toxicology. This study seeks to develop a quantitative histopathological index (Ih) and inflammation score as biomarkers in the aim to assess the health status of nanoparticles exposed mussels.Methods: Digestive gland hematoxylin and eosin (H&E) stained sections from Mytilus galloprovincialis were assessed after in vivo exposure (for 3, 6 and 12 h) to silver nanoparticles (Ag-NPs < 50 nm and Ag-NPs < 100 nm) prior and after manipulating the potential uptake pathways (clathrin- and caveolae-mediated endocytosis) using amantadine and nystatin as blockers. Quantitative models evaluate the impacts of nanoparticles size, as well as their uptake routes within different time of exposure on the inflammation intensity, the digestive tubules histomorphometry and the histopathological indices.Results: Silver nanoparticles clearly induced histopathological alterations in digestive gland (maximum inflammation 2.75 with AgNP < 100 nm [p < 0.05]; significant Ih with AgNP < 50 nm and AgNP < 100 nm at different time-points [p < 0.05]). Significant Ih were recorded after uptake routes were blockade: AgNP < 50 nm + nystatin and AgNP < 100 nm + amantadine; [p < 0.05] all time-points.Conclusions: Histopathological assessments showed to be promising tool in nanotoxicity which seems to depend on nanoparticles size, exposure time and interestingly to uptake routes. It was not clear: is it the length of exposure or the size of particles is more impactful.