dc.description.abstract |
The rapid development of nanotechnology has caused concerns about
nanoproducts on human health throughout their lifecycle. As part of the consortium
NEPHH (nanomaterial related environmental pollution on human health through their
life cycle, funded by EU-FP7), this project aimed to assess the potential effect of novel
polymer-silicon composites on human health from a lifecycle perspective, focusing on
in vitro toxicity of raw silica nanoparticles (SiNP) and dust nanoparticles (NP) released
from silicon-based polymer composites. The main objectives were to characterise a
group of amorphous SiNP and dust NP in water and cell culture medium; assess NP
toxicity potential in in vitro models; and establish mode of SiNP action.
The selection of SiNP of size 7-14 nm was based on their wide use in
developing polymer nanocomposites. Dust NP were generated from mechanical
processing of polymer composites made of polyamide-6 (PA6), polyurethane (PU) and
polypropylene (PP), each incorporated with SiNP or 3 other different silicon
reinforcement materials. The dispersion and size of NP in water and in cell culture
medium were characterized using dynamic light scattering, scanning electron
microscopy and transmission electron microscopy. The chemical composition of NP
was assessed by infra-red spectroscopy. NP were assessed in vitro for induction of
membrane damage, intracellular reactive oxygen species (ROS), loss of cell viability,
and cellular uptake by flow cytometry and confocal microscopy. In order to identify
potential biomarkers for toxicity prediction, miRNA array and extracellular
metabonomic assays were performed.
The size of SiNP (10-100 µg/ml) ranged from ~200-500 nm in water and ~20-
500 nm in culture medium, indicating the presence of aggregates. The infra-red
spectrum of SiNP dried from culture medium showed a slight difference as compared
with that dried from water, indicating protein adsorption. SiNP induced acute ROS
increase, cell membrane damage, and reduction in cell viability after 48 h in human lung
carcinoma epithelial A549 cells, lung fibroblast MRC-5 cells and skin HaCaT
keratinocytes. SiNP were up taken by all 3 cell types, and located in the cytosol. Six
early (<48h) SiNP responsive miRNAs were identified in A549 cells. SiNP also induced early changes in metabolites including glucose, lactate, ethanol, phenylalanine, histidine
and tyrosine. Dust NP generated from PA6 group materials were more toxic than those
from other polymer composites when assessed at 25-100 µg/ml at 72 h in A549 cells.
The results obtained from this study suggest that 1) both small and larger SiNP
aggregates are taken up into the target cells; 2) conventional cytotoxicity assays
combined with miRNA and metabonomic assays provide insight into the molecular
mechanisms of the nanotoxicity; 3) metabonomics and miRNA assays can serve as
robust tools for recognising sub-toxic dose-effect relationships; 4) the toxicity of dust
NP from polymer composites depends on polymer type but not reinforcement materials.
This study demonstrated the importance of lifecycle analysis as opposed to single stage
analysis of novel materials. Further studies need to improve study design to enable
interpretation of cytotoxicity in relation to NP size, physiochemical property and
intracellular dose, and to simulate the health effect of polymer-silicon composites under
more realistic scenarios. |
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