Pre-exposure to Fe 2 O 3 or TiO 2 Nanoparticles Inhibits Subsequent Biological Uptake of 55 Fe-Labeled Fe 2 O 3 Nanoparticles.

Aquatic organisms are frequently exposed to various nanoparticles (NPs) in the natural environment. Thus, studies of NP bioaccumulation should include organisms that have been previously exposed to NPs. Our study investigated the effects of pre-exposure of Tetrahymena thermophila ( T. thermophila ) to Fe 2 O 3 or TiO 2 NPs on the protozoan's subsequent uptake of 55 Fe-labeled Fe 2 O 3 ( 55 Fe 2 O 3 ) NPs. Molecular mechanisms underlying the pre-exposure effects were explored in transcriptomic and metabolomic experiments. Pre-exposure to either NPs inhibited the subsequent uptake of 55 Fe 2 O 3 NPs. The results of the transcriptomic experiment indicated that NP pre-exposure influenced the expression of genes related to phagosomes and lysosomes and physiological processes such as glutathione and lipid metabolism, which are closely associated with the endocytosis of 55 Fe 2 O 3 NPs. The differentially expressed metabolites obtained from the metabolomic experiments showed an enrichment of energy metabolism and antioxidation pathways in T. thermophila pre-exposed to NPs. Together, these results demonstrate that the pre-exposure of T. thermophila to Fe 2 O 3 or TiO 2 NPs inhibited the protozoan's subsequent uptake of 55 Fe 2 O 3 NPs, possibly by mechanisms involving the alteration of endocytosis-related organelles, the induction of oxidative stress, and a lowering of the intracellular energy supply. Thus, NP pre-exposure represents a scenario which can inform increasingly realistic estimates of NP bioaccumulation.