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

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.

Disruption of pulmonary resolution mediators contribute to exacerbated silver nanoparticle-induced acute inflammation in a metabolic syndrome mouse model.

Pre-existing conditions modulate sensitivity to numerous xenobiotic exposures such as air pollution. Specifically, individuals suffering from metabolic syndrome (MetS) demonstrate enhanced acute inflammatory responses following particulate matter inhalation. The mechanisms associated with these exacerbated inflammatory responses are unknown, impairing interventional strategies and our understanding of susceptible populations. We hypothesize MetS-associated lipid dysregulation influences mediators of inflammatory resolution signaling contributing to increased acute pulmonary toxicity. To evaluate this hypothesis, healthy and MetS mouse models were treated with either 18-hydroxy eicosapentaenoic acid (18-HEPE), 14-hydroxy docosahexaenoic acid (14-HDHA), 17-hydroxy docosahexaenoic acid (17-HDHA), or saline (control) via intraperitoneal injection prior to oropharyngeal aspiration of silver nanoparticles (AgNP). In mice receiving saline treatment, AgNP exposure resulted in an acute pulmonary inflammatory response that was exacerbated in MetS mice. A targeted lipid assessment demonstrated 18-HEPE, 14-HDHA, and 17-HDHA treatments altered lung levels of specialized pro-resolving lipid mediators (SPMs). 14-HDHA and 17-HDHA treatments more efficiently reduced the exacerbated acute inflammatory response in AgNP exposed MetS mice as compared to 18-HEPE. This included decreased neutrophilic influx, diminished induction of inflammatory cytokines/chemokines, and reduced alterations in SPMs. Examination of SPM receptors determined baseline reductions in MetS mice compared to healthy as well as decreases due to AgNP exposure. Overall, these results demonstrate AgNP exposure disrupts inflammatory resolution, specifically 14-HDHA and 17-HDHA derived SPMs, in MetS contributing to exacerbated acute inflammatory responses. Our findings identify a potential mechanism responsible for enhanced susceptibility in MetS that can be targeted for interventional therapeutic approaches.

Comparative long-term toxicity of Libby amphibole and amosite asbestos in rats after single or multiple intratracheal exposures.

In former mine workers of Libby, MT, exposure to amphibole-containing vermiculite was linked to increased rates of asbestosis, lung cancer, and mesothelioma. Although many studies showed adverse effects following exposure to Libby amphibole (LA; a mixture of winchite, richterite, and tremolite), little is known regarding the relative toxicity of LA compared to regulated asbestos, or regarding the risks associated with acute high-dose exposures relative to repeated low-dose exposures. In this study, pulmonary function, inflammation, and pathology were assessed after single or multiple intratracheal (IT) exposures of LA or a well-characterized amosite (AM) control fiber with equivalent fiber characteristics. Male F344 rats were exposed to an equivalent total mass dose (0.15, 0.5, 1.5, or 5 mg/rat) of LA or AM administered either as a single IT instillation, or as multiple IT instillations given every other week over a 13-wk period, and necropsied up to 20 mo after the initial IT. When comparing the two fiber types, in both studies LA resulted in greater acute neutrophilic inflammation and cellular toxicity than equal doses of AM, but long-term histopathological changes were approximately equivalent between fibers, suggesting that LA is at least as toxic as AM. In addition, although no dose-response relationship was discerned, mesothelioma or lung carcinomas were found after exposure to low and high dose levels of LA or AM in both studies. Conversely, when comparing studies, an equal mass dose given over multiple exposures instead of a single bolus resulted in greater chronic pathological changes in lung at lower doses, despite the initially weaker acute inflammatory response. Overall, these results suggest that there is a possibility of greater long-term pathological changes with repeated lower LA dose exposures, which more accurately simulates chronic environmental exposures.

Silver nanoparticle protein corona composition in cell culture media.

The potential applications of nanomaterials as drug delivery systems and in other products continue to expand. Upon introduction into physiological environments and driven by energetics, nanomaterials readily associate proteins forming a protein corona (PC) on their surface. This PC influences the nanomaterial's surface characteristics and may impact their interaction with cells. To determine the biological impact of nanomaterial exposure as well as nanotherapeutic applications, it is necessary to understand PC formation. Utilizing a label-free mass spectrometry-based proteomics approach, we examined the composition of the PC for a set of four silver nanoparticles (AgNPs) including citrate-stabilized and polyvinlypyrrolidone-stabilized (PVP) colloidal silver (20 or 110 nm diameter). To simulate cell culture conditions, AgNPs were incubated for 1 h in Dulbecco's Modified Eagle Medium supplemented with 10% fetal bovine serum, washed, coronal proteins solubilized, and proteins identified and quantified by label-free LC-MS/MS. To determine which attributes influence PC formation, the AgNPs were characterized in both water and cell culture media with 10% FBS. All AgNPs associated a common subset of 11 proteins including albumin, apolipoproteins, keratins, and other serum proteins. 110 nm citrate- and PVP-stabilized AgNPs were found to bind the greatest number of proteins (79 and 85 respectively) compared to 20 nm citrate- and PVP-stabilized AgNPs (45 and 48 respectively), suggesting a difference in PC formation based on surface curvature. While no relationships were found for other protein parameters (isoelectric point or aliphatic index), the PC on 20 nm AgNPs (PVP and citrate) consisted of more hydrophobic proteins compared to 110 nm AgNPs implying that this class of proteins are more receptive to curvature-induced folding and crowding in exchange for an increased hydration in the aqueous environment. These observations demonstrate the significance of electrostatic and hydrophobic interactions in the formation of the PC which may have broad biological and toxicological implications.

Pulmonary inflammatory and fibrotic responses in Fischer 344 rats after intratracheal instillation exposure to Libby amphibole.

Increased incidences of asbestosis have been reported in workers from Libby, MT, associated with exposures to amphibole-contaminated vermiculite. In this study pulmonary and histopathological changes were investigated following Libby amphibole (LA) exposure in a rat model. Rat respirable fractions of LA and amosite (aerodynamic diameter <2.5 µm) were prepared by water elutriation. Male F344 rats were exposed to single doses of either saline (SAL), amosite (0.65 mg/rat), or LA (0.65 or 6.5 mg/rat) by intratracheal instillation. At times from 1 d to 3 mo after exposure, bronchoalveolar lavage (BAL) was performed and right and left lungs were removed for reverse-transcription polymerase chain reaction (RT-PCR) and histopathological analysis, respectively. Data indicated that 0.65 mg amosite resulted in a higher degree of pulmonary injury, inflammation, and fibrotic events than LA at the same mass dose. Exposure to either amosite or high dose LA resulted in higher levels of cellular permeability and injury, inflammatory enzymes, and iron binding proteins in both BAL fluid and lung tissue at most time points when compared to SAL controls. However, mRNA expression for some growth factors (e.g., platelet-derived growth factor [PDGF]-A and transforming growth factor [TGF]-1ß), which contribute to fibrosis, were downregulated at several time points. Furthermore, histopathological examination showed notable thickening of interstitial areas surrounding the alveolar ducts and terminal bronchioles. On a mass dose basis, amosite produced a greater acute and persistent lung injury for at least 3 mo after exposure. However, further testing and analysis of LA are needed with regard to the dose metric to fully evaluate its potential fibrogenicity and carcinogenicity.