Enhanced silver nanoparticle-induced pulmonary inflammation in a metabolic syndrome mouse model and resolvin D1 treatment

Abstract

Background: Metabolic syndrome (MetS) exacerbates susceptibility to inhalation exposures such as particulate air pollution, however, the mechanisms responsible remain unelucidated. Previously, we determined a MetS mouse model exhibited exacerbated pulmonary inflammation 24 h following AgNP exposure compared to a healthy mouse model. This enhanced response corresponded with reduction of distinct resolution mediators. We hypothesized silver nanoparticle (AgNP) exposure in MetS results in sustained pulmonary inflammation. Further, we hypothesized treatment with resolvin D1 (RvD1) will reduce exacerbations in AgNP-induced inflammation due to MetS.

Results: To evaluate these hypotheses, healthy and MetS mouse models were exposed to vehicle (control) or AgNPs and a day later, treated with resolvin D1 (RvD1) or vehicle (control) via oropharyngeal aspiration. Pulmonary lung toxicity was evaluated at 3-, 7-, 14-, and 21-days following AgNP exposure. MetS mice exposed to AgNPs and receiving vehicle treatment, demonstrated exacerbated pulmonary inflammatory responses compared to healthy mice. In the AgNP exposed mice receiving RvD1, pulmonary inflammatory response in MetS was reduced to levels comparable to healthy mice exposed to AgNPs. This included decreases in neutrophil influx and inflammatory cytokines, as well as elevated anti-inflammatory cytokines.

Conclusions: Inefficient resolution may contribute to enhancements in MetS susceptibility to AgNP exposure causing an increased pulmonary inflammatory response. Treatments utilizing specific resolution mediators may be beneficial to individuals suffering MetS following inhalation exposures.

Keywords: Chronic inflammation; Failure of resolution; Inflammatory resolution; Lipid supplementation; Metabolic syndrome (MetS); Nanoparticles (NPs); Nanotoxicity; Omega-3 polyunsaturated fatty acids; Resolvin D1 (RvD1); Specialized pro-resolving mediators (SPMs); Susceptibility.

Fig. 1

Experiment Design Timeline. Mice were fed a healthy or high-fat western diet for 14 weeks and exposed to either water (control) or AgNPs (50 µg) via oropharyngeal aspiration. 24 h post-exposure, mice were treated with saline (control) or RvD1 (400 ng) via oropharyngeal aspiration. Endpoints associated with inflammation and lipid metabolism were examined at 3-, 7-, 14-, and 21-days following AgNP exposure

Fig. 2

Chronic effect of AgNP exposure and modulation by RvD1 treatment on BALF A total protein, B total cell counts, C macrophage counts, and D neutrophil counts from healthy and MetS mice. 24 h following oropharyngeal aspiration of pharmaceutical grade sterile water (control) or AgNPs (50 µg) in sterile water, mice were oropharyngeal aspiration with 400 ng RvD1 or sterile saline (vehicle). Endpoints were evaluated at 3-, 7-, 14- and 21-days post AgNP exposures. Values are expressed as mean ± S.E.M. * AgNP exposure; # disease model; $ treatment; and t time point (p < 0.05)

Fig. 3

Hyperspectral analysis of AgNPs within macrophages collected from BAL fluid healthy and MetS mouse models. A Representative enhanced darkfield images of macrophages at 3, 7, 14, and 21 days following AgNP exposure at 50 µg from healthy and MetS mice not receiving RvD1 treatment. B Representative enhanced darkfield images of macrophages at 3, 7, 14, and 21 days following AgNP exposure from healthy and MetS mice receiving 400 ng RvD1 treatment. At least 1000 pixels of AgNPs were collected from mean spectra and then all spectra were normalized based on intensity for comparisons. White bar identifies 10 µm scaling. Representative images of internalized cells and spectral profiles of internalized AgNPs over the study time course can be found in Supplemental Fig. 2–4

Fig. 4

Chronic effect of AgNP exposure and modulation by RvD1 treatment on pulmonary inflammatory gene expression including A Interleukin-6 (IL-6), B macrophage inflammatory protein-2 (MIP-2), C monocyte chemoattractant-1 (MCP-1), and D tumor necrosis factor alpha (TNF-α) from healthy and MetS mice. 24 h following oropharyngeal aspiration of pharmaceutical grade sterile water (control) or AgNPs (50 µg) in sterile water, mice were oropharyngeal aspiration with 400 ng RvD1 or sterile saline (vehicle). Endpoints were evaluated at 3-, 7-, 14- and 21-days post AgNP exposures. Values are expressed as mean ± S.E.M. * AgNP exposure; # disease model; $ treatment; and t time point (p < 0.05)

Fig. 5

Chronic effect of AgNP exposure and modulation by RvD1 treatment on pulmonary anti-inflammatory gene expression including A Interleukin-10 (IL-10) and B Interleukin-4 (IL-4) from healthy and MetS mice. 24 h following oropharyngeal aspiration of pharmaceutical grade sterile water (control) or AgNPs (50 µg) in sterile water, mice were oropharyngeal aspiration with 400 ng RvD1 or sterile saline (vehicle). Endpoints were evaluated at 3-, 7-, 14- and 21-days post AgNP exposures. Values are expressed as mean ± S.E.M. * AgNP exposure; # disease model; $ treatment; and t time point (p < 0.05)

Fig. 6

Chronic effect of AgNP exposure and modulation by RvD1 treatment on pulmonary gene expression associated with lipid metabolism including A Arachidonate 5-lipoxygenase (ALOX-5), B arachidonate 15-lipoxygenase (ALOX-15), C inducible nitric oxide synthase (iNOS), and D phospholipase A2 (iPLA2) from healthy and MetS mice. 24 h following oropharyngeal aspiration of pharmaceutical grade sterile water (control) or AgNPs (50 µg) in sterile water, mice were oropharyngeal aspiration with 400 ng RvD1 or sterile saline (vehicle). Endpoints were evaluated at 3-, 7-, 14- and 21-days post AgNP exposures. Values are expressed as mean ± S.E.M. * AgNP exposure; # disease model; $ treatment; and t time point (p < 0.05)

Fig. 7

Chronic effect of AgNP exposure and modulation by RvD1 treatment on pulmonary inflammatory protein level including A macrophage inflammatory protein-2 and B monocyte chemoattractant-1 protein levels from BAL fluid healthy and MetS mice. 24 h following oropharyngeal aspiration of pharmaceutical grade sterile water (control) or AgNPs (50 µg) in sterile water, mice were oropharyngeal aspiration with 400 ng RvD1 or sterile saline (vehicle). Endpoints were evaluated at 3-, 7-, 14- and 21-days post AgNP exposures. Values are expressed as mean ± S.E.M. * AgNP exposure; # disease model; $ treatment; and t time point (p < 0.05)

Fig. 8

Chronic effect of AgNP exposure and modulation by RvD1 treatment on pulmonary pro-inflammatory resolution protein level A Interleukin 10 protein and on lipid involved in inflammatory resolution B Resolvin D1 levels from BAL fluid healthy and MetS mice. 24 h following oropharyngeal aspiration of pharmaceutical grade sterile water (control) or AgNPs (50 µg) in sterile water, mice were oropharyngeal aspiration with 400 ng RvD1 or sterile saline (vehicle). Endpoints were evaluated at 3-, 7-, 14- and 21-days post AgNP exposures. Values are expressed as mean ± S.E.M. * AgNP exposure; # disease model; $ treatment; and t time point (p < 0.05)