In Vivo Metabolic Response upon Exposure to Gold Nanorod Core/Silver Shell Nanostructures: Modulation of Inflammation and Upregulation of Dopamine

Abstract

With the increasing applications of silver nanoparticles (Ag NPs), the concerns of widespread human exposure as well as subsequent health risks have been continuously growing. The acute and chronic toxicities of Ag NPs in cellular tests and animal tests have been widely investigated. Accumulating evidence shows that Ag NPs can induce inflammation, yet the overall mechanism is incomplete. Herein, using gold nanorod core/silver shell nanostructures (Au@Ag NRs) as a model system, we studied the influence on mice liver and lungs from the viewpoint of metabolism. In agreement with previous studies, Au@Ag NRs' intravenous exposure caused inflammatory reaction, accompanying with metabolic alterations, including energy metabolism, membrane/choline metabolism, redox metabolism, and purine metabolism, the disturbances of which contribute to inflammation. At the same time, dopamine metabolism in liver was also changed. This is the first time to observe the production of dopamine in non-neural tissue after treatment with Ag NPs. As the upregulation of dopamine resists inflammation, it indicates the activation of antioxidant defense systems against oxidative stress induced by Au@Ag NRs. In the end, our findings deepened the understanding of molecular mechanisms of Ag NPs-induced inflammation and provide assistance in the rational design of their biomedical applications.

Keywords: dopamine; gold nanorod core/silver shell nanostructures; inflammation; metabolism.

Figure 1

Characterizations of gold nanorods core/silver shell nanostructures (Au@Ag NRs). (A,B) Typical TEM images of Au@Ag NRs; (C) TEM image of an individual Au@Ag NR and its corresponding EDS (energy disperse spectroscopy) element maps of Au, Ag, and their overlay, respectively; (D) UV-vis-NIR (ultraviolet-visible-near infrared ray) extinction spectra of Au@Ag NRs dispersed in water and 5% glucose solution, respectively.

Figure 2

Effects of Au@Ag NRs on metabolic profiles of mouse liver. (A) Metabolic cluster analysis using an orthogonal partial least squares discrimination analysis (OPLS-DA) scores plot. The component t[1] is the predicted principal component, maximumly reflecting the inter-group differences, while intra-group variation is reflected in t0. L1-N is the control group and L2-N is the mice received multiple administration of Au@Ag NRs (N = 1–10); (B) heat maps of differential metabolites. All of the data were obtained under positive mode.

Figure 3

Influence of Au@Ag NRs on liver tissue. (A) histological images of liver from mice received multiple administration of Au@Ag NRs. The tissues were stained with hematoxylin and eosin; (B) the level of tyrosine hydroxylase (TH) expression in liver visualized by immunohistochemical staining, indicated by red arrows.

Figure 4

Effects of Au@Ag NRs on Raw264.7 cells. (A) in vitro two-photon luminescence (TPL) images upon different Au@Ag NR exposure concentrations; (B) cell viability of Raw264.7 cells affected by Au@Ag NRs; (C) folds of fluorescent intensity detected with 2′,7′-Dichlorofluorescin diacetate (DCFH-DA) by flow cytometry; (D) relative level of reduced glutathione (GSH) after the treatment with Au@Ag for 24 h; (E) Western blotting results of HO-1, after exposed to Au@Ag NRs for 24 h. The * represents significant difference from control group (*: p < 0.05). The data were presented as mean ± SD (n = 3).

Figure 5

The secretion of inflammatory cytokines enhanced by Au@Ag NRs in Raw264.7 cells. (A) the secretion of IL-6, after 24 h exposure to Au@Ag NRs; (B) the IL-1β level in cultural supernatant. The * represents significant difference from control group (**: p < 0.01). The data were presented as mean ± SD (n = 3).

Figure 6

Influence of Au@Ag NRs on lung tissue. (A) IL-1β level in the lungs from mice received multiple administration of Au@Ag NRs. IL-1β was stained with red and indicated by red arrows, and the nucleus was stained with blue; (B) the level of tyrosine hydroxylase (TH) expression in the lungs visualized by immunofluorescence histochemistry. TH was stained with red and indicated by red arrows, and the nucleus was stained with blue. The inset in orange box is a magnification of the white box.

Figure 7

Summary of the main metabolic pathway alterations in the mouse liver upon exposure of Au@Ag NRs. Phosphatidylcholine (PC), lyso-phosphatidylcholine (LPC), glycerophosphocholine (GPC), phosphorylcholine (PCho), phenylalanine (Phe), tyrosine (Tyr).