Attenuation of allergic airway inflammation and hyperresponsiveness in a murine model of asthma by silver nanoparticles

Abstract

The use of silver in the past demonstrated the certain antimicrobial activity, though this has been replaced by other treatments. However, nanotechnology has provided a way of producing pure silver nanoparticles, and it shows cytoprotective activities and possible pro-healing properties. But, the mechanism of silver nanoparticles remains unknown. This study was aimed to investigate the effects of silver nanoparticles on bronchial inflammation and hyperresponsiveness. We used ovalbumin (OVA)-inhaled female C57BL/6 mice to evaluate the roles of silver nanoparticles and the related molecular mechanisms in allergic airway disease. In this study with an OVA-induced murine model of allergic airway disease, we found that the increased inflammatory cells, airway hyperresponsiveness, increased levels of IL-4, IL-5, and IL-13, and the increased NF-κB levels in lungs after OVA inhalation were significantly reduced by the administration of silver nanoparticles. In addition, we have also found that the increased intracellular reactive oxygen species (ROS) levels in bronchoalveolar lavage fluid after OVA inhalation were decreased by the administration of silver nanoparticles. These results indicate that silver nanoparticles may attenuate antigen-induced airway inflammation and hyperresponsiveness. And antioxidant effect of silver nanoparticles could be one of the molecular bases in the murine model of asthma. These findings may provide a potential molecular mechanism of silver nanoparticles in preventing or treating asthma.

Keywords: NF-κB; allergic airway disease; oxidative stress; silver nanoparticles.

Figure 1

A) Photomicrographs of silver nanoparticles (NPs). B) Transmission electron microscopic image of bulk of silver NPs. Bars in A) and B) indicate 20 nm and 5 nm, respectively.

Figure 2

Effect of silver nanoparticles (NPs) on intracellular reactive oxygen species (ROS) levels in bronchoalveolar lavage (BAL) cells from ovalbumin (OVA)-sensitized and OVA-challenged mice. Sampling was performed 72 hours after the final challenge. A–D) Representative microphotographs show the dichlorofluorescein (DCF) fluorescence intensity of cells from saline-inhaled mice administered saline A), OVA-inhaled mice administered saline B), saline-inhaled mice administered 40 mg/kg of silver NPs (C), and OVA-inhaled mice administered 40 mg/kg of silver NPs D). E–H) Corresponding transmission light microphotographs are shown. I–L) A representative frequency histogram of the fluorescence intensity of cells from saline-inhaled mice administered saline (SAL), OVA-inhaled mice administered saline (OVA), saline-inhaled mice administered 40 mg/kg of silver NPs (Ag 40), and OVA-inhaled mice administered 40 mg/kg of silver NPs (OVA + Ag 40).

Figure 3

Effect of silver nanoparticles (NPs) on the protein expression of NF-κB p65 in lung tissues collected from ovalbumin (OVA)-sensitized and OVA-challenged mice. NF-κB p65 were measured 72 hours after the final challenge in saline-inhaled mice administered saline (SAL), OVA-inhaled mice administered saline (OVA), saline-inhaled mice administered 40 mg/kg of silver NPs (Ag 40), and OVA-inhaled mice administered 40 mg/kg of silver NPs (OVA + Ag 40). A) Western blot analyses of NF-κB p65 in nuclear (Nuc) and cytosolic (Cyt) protein extracts from lung tissues. B) NF-κB p65 protein levels in (A) were quantified using a Gel-Pro Analyzer (Media Cybernetics, Silver Spring, MD, USA) and plotted as the integrated optical density, using Microsoft Excel. Bars indicate the mean ± SEM and are representative of eight independent experiments using different preparations of nuclear and cytosolic extracts. *P < 0.05 versus SAL; ^#P < 0.05 versus OVA.

Figure 4

Effect of silver nanoparticles (NPs) on IL-4, IL-5, and IL-13 expression in lung tissues collected from ovalbumin (OVA)-sensitized and OVA-challenged mice. Sampling was performed 72 hours after the final challenge in saline-inhaled mice administered saline (SAL), OVA-inhaled mice administered saline (OVA), saline-inhaled mice administered 40 mg/kg of silver NPs (Ag 40), and OVA-inhaled mice administered 40 mg/kg of silver NPs (OVA + Ag 40). A) RT-PCR results. B) Western blot analyses of IL-4, IL-5, and IL-13 in lung tissues. C) Quantification of the IL-4, IL-5, and IL-13 protein levels in B) using Gel-Pro Analyzer (Media Cybernetics, Silver Spring, MD, USA). The relative protein content was calculated as the ratio of the integrated optical density of each protein to that of actin. The ratio is arbitrarily presented as 100%. Bars indicate the mean ± SEM and are representative of eight independent experiments using different preparations of lung tissues. *P < 0.05 versus SAL; ^#P < 0.05 versus OVA.

Figure 5

Effect of silver nanoparticles (NPs) on bronchial inflammation in ovalbumin (OVA)-sensitized and OVA-challenged mice. Sampling was performed 72 hours after the final challenge in saline-inhaled mice administered saline (SAL), OVA-inhaled mice administered saline (OVA), saline-inhaled mice administered 40 mg/kg of silver NPs (Ag 40), and OVA-inhaled mice administered 40 mg/kg of silver NPs (OVA + Ag 40). A−D) Representative H&E-stained sections of the lungs. Bars indicate scale of 50 μm. E) Total lung inflammation scores. F) The numbers of total and differential cellular components of bronchoalveolar lavage (BAL) fluids. Bars indicate the mean ± SEM for eight mice per group in four to six independent experiments. *P < 0.05 versus SAL; ^#P < 0.05 versus OVA.

Figure 6

Effect of silver nanoparticles (NPs) on airway responsiveness to inhaled methacholine in ovalbumin (OVA)-sensitized and OVA-challenged mice. Airway hyperresponsiveness was measured at 48 h after the final challenge in saline-inhaled mice administered saline (SAL), OVA-inhaled mice administered saline (OVA), saline-inhaled mice administered 40 mg/kg of silver NPs (Ag 40), and OVA-inhaled mice administered 40 mg/kg of silver NPs (OVA + Ag 40). Penh values were obtained in response to increasing doses (2.5–50 mg/mL) of methacholine. Bars indicate the mean ± SEM for eight mice per group in four to six independent experiments. *P < 0.05 versus SAL; ^#P < 0.05 versus OVA.