Time-course profiling of molecular stress responses to silver nanoparticles in the earthworm Eisenia fetida

The molecular mechanism of silver nanoparticle (AgNP) toxicity, particularly its temporal aspect, is currently limited in the literature. This study seeks to identify and profile changes in molecular response patterns over time during soil exposure of the earthworm Eisenia fetida to AgNPs (82±27 nm) with reference to dissolved silver salt (AgNO₃). Principal component analysis of selected gene and enzyme response profiles revealed dissimilar patterns between AgNO₃ and AgNP treatments and also over time. Despite the observed difference in molecular profiles, the body burdens of total Ag were within the same range (10-40 mg/kg dry weight worm) for both treatments with apparent correlation to the induction pattern of metallothionein. AgNO₃ induced the genes and enzymes related to oxidative stress at day 1, after which markers of energy metabolism were all suppressed at day 2. Exposure to AgNPs likewise led to induction of oxidative stress genes at day 2, but with a temporal pattern shift to immune genes at day 14 following metabolic upregulation at day 7. The involvement of oxidative stress and subsequent alterations in immune gene regulation were as predicted by our in vitro study reported previously, highlighting the importance of immunological endpoints in nanosilver toxicity.