Unbound Natural Organic Matter Competes with Nanoparticles for Internalization Receptors During Cell Uptake

Cell-excreted proteins mediate the interactions of differently sized silica nanoparticles during cellular uptake

Exposure to different types of nanoparticles (NPs) results in their deposition in human bodies. While most studies have examined the cellular uptake of only one type of NP at a time, how the dynamics of NP uptake may change in the presence of other types of NPs remains unclear. We therefore investigated the interplay of two differently sized SiO2 NPs during their uptake by A549 human lung carcinoma cells. Both NPs contained a CdSeTe core, which was labeled with different Cd isotopes to differentiate between them. Our study showed that the uptake of one size of SiO2 NPs either increased or decreased with the concentration of the other size of SiO2 NPs. This variation in uptake was attributable to the concentration-dependent aggregation of SiO2 NPs, as determined by the amount of cell-excreted proteins adsorbed on the NP surface. Further, the effects of the protein corona on the attachment of SiO2 NPs to the cell surface and uptake competition between differently sized SiO2 NPs also played important roles. Cell-excreted proteins were then analyzed by proteomics. Overall, the complex interactions between coexisting NPs of different physicochemical properties and cell-excreted proteins should be considered during bio-applications and bio-safety evaluations of NPs.

Silica nanoparticles inhibit cadmium uptake by the protozoan Tetrahymena thermophila without the need for adsorption

The simultaneous presence of nanoparticles (NPs) and heavy metals in the environment may affect their mutual biological uptake. Although previous studies showed that NPs could alter the cellular uptake of heavy metals by their adsorption of heavy metals, whether they could affect metal uptake without the need for adsorption is unknown. This study examined the effects of silica (SiO2) NPs on the uptake of Cd ion by the protozoan Tetrahymena thermophila. We found that, even with negligible levels of adsorption, SiO2 NPs at concentrations of 3 to 100 mg/L inhibited Cd uptake. This inhibitory effect decreased as the ambient Cd concentration increased from 1 to 100 μg/L, suggesting the involvement of at least two transporters with different affinities for Cd. The transporters were subsequently identified by the specific protein inhibitors amiloride and tariquidar as NCX and ABCB1, which are responsible for the uptake of Cd at low and high Cd levels, respectively. RT-qPCR and molecular dynamics simulation further showed that the inhibitory effects of SiO2 NPs were attributable to the down-regulated expression of the genes Ncx and Abcb1, steric hindrance of Cd uptake by NCX and ABCB1, and the shrinkage of the central channel pore of the transporters in the presence of SiO2 NPs. SiO2 NPs more strongly inhibited Cd transport by NCX than by ABCB1, due to the higher binding affinity of SiO2 NPs with NCX. Overall, our study sheds new light on a previously overlooked influence of NPs on metal uptake and the responsible mechanism.

Silica Nanoparticle Size Determines the Mechanisms Underlying the Inhibition of Iron Oxide Nanoparticle Uptake by Daphnia magna

Aquatic environments are complicated systems that contain different types of nanoparticles (NPs). Nevertheless, recent studies of NP toxicity, and especially those that have focused on bioaccumulation have mostly investigated only a single type of NPs. Assessments of the environmental risks of NPs that do not consider co-exposure regimes may lead to inaccurate conclusions and ineffective environmental regulation. Thus, the present study examined the effects of differently sized silica NPs (SiO2 NPs) on the uptake of iron oxide NPs (Fe2O3 NPs) by the zooplankton Daphnia magna. Both SiO2 NPs and Fe2O3 NPs were well dispersed in the experimental medium without significant heteroaggregation. Although all three sizes of SiO2 NPs inhibited the uptake of Fe2O3 NPs, the underlying mechanisms differed. SiO2 NPs smaller than the average mesh size (∼200 nm) of the filtering apparatus of D. magna reduced the accumulation of Fe2O3 NPs through uptake competition, whereas larger SiO2 NPs inhibited the uptake of Fe2O3 NPs mainly by reducing the water filtration rate of the daphnids. Overall, in evaluations of the risks of NPs in the natural environment, the different mechanisms underlying the effects of NPs of different sizes on the uptake of dissimilar NPs should be considered.

Silica nanoparticle accumulation in plants: current state and future perspectives

With their excellent biocompatibility, adjustable size, and high specific surface area, silica nanoparticles (SiO2 NPs) offer an alternative to traditional bulk fertilizers as a means to promote sustainable agriculture. SiO2 NPs have been shown to promote the growth of plants and to reduce the negative effects of biotic and abiotic stresses, but their bioaccumulation is a crucial factor that has been overlooked in studies of their biological effects. In this review, the techniques to quantify and visualize SiO2 NPs in plants were examined first. We then provide a summary of the current state of knowledge on the accumulation, translocation, and transformation of SiO2 NPs in plants and of the factors (e.g., the physicochemical properties of SiO2 NPs, plant species, application mode, and environmental conditions) that influence SiO2 NP bioaccumulation. The challenges in analyzing NP-plant interactions are considered as well. We conclude by identifying areas for further research that will advance our understanding of NP-plant interactions and thus contribute to more sustainable, eco-friendly, nano-enabled approaches to improving crop nutrient supplies. The information presented herein is important to improve the delivery efficiency of SiO2 NPs for precision and sustainable agriculture and to assess the safety of SiO2 NPs during their application in agriculture.

Pre-exposure to Fe2O3 or TiO2 Nanoparticles Inhibits Subsequent Biological Uptake of 55Fe-Labeled Fe2O3 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 Fe₂O₃ or TiO₂ NPs on the protozoan's subsequent uptake of ⁵⁵Fe-labeled Fe₂O₃ (⁵⁵Fe₂O₃) 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 ⁵⁵Fe₂O₃ 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 ⁵⁵Fe₂O₃ 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 Fe₂O₃ or TiO₂ NPs inhibited the protozoan's subsequent uptake of ⁵⁵Fe₂O₃ 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.