Intracellular trafficking pathways in silver nanoparticle uptake and toxicity in <i>Caenorhabditis elegans</i>

We used the nematode <i>Caenorhabditis elegans</i> to study the roles of endocytosis and lysosomal function in uptake and subsequent toxicity of silver nanoparticles (AgNP) <i>in vivo</i>. To focus on AgNP uptake and effects rather than silver ion (AgNO₃) effects, we used a minimally dissolvable AgNP, citrate-coated AgNPs (CIT-AgNPs). We found that the clathrin-mediated endocytosis inhibitor chlorpromazine reduced the toxicity of CIT-AgNPs but not AgNO₃. We also tested the sensitivity of three endocytosis-deficient mutants (<i>rme-1, rme-6</i> and <i>rme-8</i>) and two lysosomal function deficient mutants (<i>cup-5</i> and <i>glo-1</i>) as compared to wild-type (N2 strain). One of the endocytosis-deficient mutants (<i>rme-6</i>) took up less silver and was resistant to the acute toxicity of CIT-AgNPs compared to N2s. None of those mutants showed altered sensitivity to AgNO₃. Lysosome and lysosome-related organelle mutants were more sensitive to the growth-inhibiting effects of both CIT-AgNPs and AgNO₃. Our study provides mechanistic evidence suggesting that early endosome formation is necessary for AgNP-induced toxicity <i>in vivo</i>, as <i>rme-6</i> mutants were less sensitive to the toxic effects of AgNPs than <i>C. elegans</i> with mutations involved in later steps in the endocytic process.