Changes in Gut Microbiota Structure: A Potential Pathway for Silver Nanoparticles to Affect the Host Metabolism

Silver
nanoparticles (AgNPs) are one of the most widely used NPs.
Their adverse effects on either the host or its gut microbiota (GM)
have been examined. Nevertheless, whether the GM plays any role in
AgNP toxicity to the host remains unclear. In the present study, AgNPs
were administered to mice by oral gavage once a day for 120 days.
A significant dose-dependent accumulation of Ag in the liver was observed,
with a steady state reached within 21 days. The AgNPs changed the
structure of the GM, mainly with respect to microorganisms involved
in the metabolism of energy, amino acids, organic acids, and lipids,
as predicted in a PICRUST analysis. Effects of the AgNPs on liver
metabolism were also demonstrated, as a KEGG pathway analysis showed
the enrichment of pathways responsible for the metabolism of amino
acids, purines and pyrimidine, lipids, and energy. More interestingly,
the changes in GM structure and liver metabolism were highly correlated,
evidenced by the correlation between ∼23% of the differential
microorganisms at the genus level and ∼60% of the differential
metabolites. This implies that the metabolic variations in liver as
affected by AgNPs were partly attributable to NP-induced changes of
GM structure. Therefore, our results demonstrate the importance of
considering the roles of GM in the toxicity of NPs to the host in
evaluations of the health risks of NPs.