Amorphous silica nanoparticles caused lung injury through the induction of epithelial apoptosis via ROS/Ca2+/DRP1-mediated mitochondrial fission signaling

Silica nanoparticles triggered epithelial ferroptosis via miR-21-5p/GCLM signaling to contribute to fibrogenesis in the lungs

The toxicity of silica nanoparticles (SiNPs) to lung is known. We previously demonstrated that exposure to SiNPs promoted pulmonary impairments, but the precise pathogenesis remains elucidated. Ferroptosis has now been identified as a unique form of oxidative cell death, but whether it participated in SiNPs-induced lung injury remains unclear. In this work, we established a rat model with sub-chronic inhalation exposure of SiNPs via intratracheal instillation, and conducted histopathological examination, iron detection, and ferroptosis-related lipid peroxidation and protein assays. Moreover, we evaluated the effect of SiNPs on epithelial ferroptosis, possible mechanisms using in vitro-cultured human bronchial epithelial cells (16HBE), and also assessed the ensuing impact on fibroblast activation for fibrogenesis. Consequently, fibrotic lesions occurred in the rat lungs, concomitantly by enhanced lipid peroxidation, iron overload, and ferroptosis. Consistently, the in vitro data showed SiNPs triggered oxidative stress and caused the accumulation of lipid peroxides, resulting in ferroptosis. Importantly, the mechanistic investigation revealed miR-21-5p as a key player in the epithelial ferroptotic process induced by SiNPs via targeting GCLM for GSH depletion. Of note, ferrostatin-1 could greatly suppress ferroptosis and alleviate epithelial injury and ensuing fibroblast activation by SiNPs. In conclusion, our findings first revealed SiNPs triggered epithelial ferroptosis through miR-21-5p/GCLM signaling and thereby promoted fibroblast activation for fibrotic lesions, and highlighted the therapeutic potential of inhibiting ferroptosis against lung impairments upon SiNPs exposure.

Epithelium-derived exosomes promote silica nanoparticles-induced pulmonary fibroblast activation and collagen deposition via modulating fibrotic signaling pathways and their epigenetic regulations

BACKGROUND

In the context of increasing exposure to silica nanoparticles (SiNPs) and ensuing respiratory health risks, emerging evidence has suggested that SiNPs can cause a series of pathological lung injuries, including fibrotic lesions. However, the underlying mediators in the lung fibrogenesis caused by SiNPs have not yet been elucidated.

RESULTS

The in vivo investigation verified that long-term inhalation exposure to SiNPs induced fibroblast activation and collagen deposition in the rat lungs. In vitro, the uptake of exosomes derived from SiNPs-stimulated lung epithelial cells (BEAS-2B) by fibroblasts (MRC-5) enhanced its proliferation, adhesion, and activation. In particular, the mechanistic investigation revealed SiNPs stimulated an increase of epithelium-secreted exosomal miR-494-3p and thereby disrupted the TGF-β/BMPR2/Smad pathway in fibroblasts via targeting bone morphogenetic protein receptor 2 (BMPR2), ultimately resulting in fibroblast activation and collagen deposition. Conversely, the inhibitor of exosomes, GW4869, can abolish the induction of upregulated miR-494-3p and fibroblast activation in MRC-5 cells by the SiNPs-treated supernatants of BEAS-2B. Besides, inhibiting miR-494-3p or overexpression of BMPR2 could ameliorate fibroblast activation by interfering with the TGF-β/BMPR2/Smad pathway.

CONCLUSIONS

Our data suggested pulmonary epithelium-derived exosomes serve an essential role in fibroblast activation and collagen deposition in the lungs upon SiNPs stimuli, in particular, attributing to exosomal miR-494-3p targeting BMPR2 to modulate TGF-β/BMPR2/Smad pathway. Hence, strategies targeting exosomes could be a new avenue in developing therapeutics against lung injury elicited by SiNPs.

Comprehensive pulmonary metabolic responses to silica nanoparticles exposure in Fisher 344 rats

Silica nanoparticles (SiNPs) could induce adverse pulmonary effects, but the mechanism was not clear enough. Metabolomics is a sensitive and high-throughput approach that could investigate the intrinsic causes of adverse health effects caused by SiNPs. The current investigation represented the first in vivo metabolomics study examining the chronic pulmonary toxicity of SiNPs at a low dosage, mimicking real human exposure situation. The recovery process after the cessation of exposure was also taken into consideration. Fisher 344 rats were treated with either saline or SiNPs for 6 months. Half of the animals in each group received an additional six-month period for recovery. The findings indicated that chronic low-level exposure to SiNPs resulted in notable alterations in pulmonary metabolism of amino acids, lipids, carbohydrates, and nucleotides. SiNPs exerted an impact on various metabolites and metabolic pathways which are linked to oxidative stress, inflammation and tumorigenesis. These included but were not limited to L-carnitine, spermidine, taurine, xanthine, and glutathione metabolism. The metabolic alterations caused by SiNPs exhibited a degree of reversibility. However, the interference of SiNPs on two metabolic pathways related to tumorigenesis was observed to persist after a recovery period. The two metabolic pathways are glycerophospholipid metabolism as well as phenylalanine, tyrosine and tryptophan biosynthesis. This study elucidated the metabolic alterations induced by chronic low-level exposure to SiNPs and presented novel evidence of the chronic pulmonary toxicity and carcinogenicity of SiNPs, from a metabolomic perspective.

Advances in the study of silica nanoparticles in lung diseases

Silicon dioxide nanoparticles (SiNPs) are one of the major forms of silicon dioxide and are composed of the most-abundant compounds on earth. Based on their excellent properties, SiNPs are widely used in food production, synthetic processes, medical diagnostics, drug delivery, and other fields. The mass production and wide application of SiNPs increases the risk of human exposure to SiNPs. In the workplace and environment, SiNPs mainly enter the human body through the respiratory tract and reach the lungs; therefore, the lungs are the most important and most toxicologically affected target organ of SiNPs. An increasing number of studies have shown that SiNP exposure can cause severe lung toxicity. However, studies on the toxicity of SiNPs in ex vivo and in vivo settings are still in the exploratory phase. The molecular mechanisms underlying the lung toxicity of SiNPs are varied and not yet fully understood. As a result, this review summarizes the possible mechanisms of SiNP-induced lung toxicity, such as oxidative stress, endoplasmic reticulum stress, mitochondrial damage, and cell death. Moreover, this study provides a summary of the progression of diseases caused by SiNPs, thereby establishing a theoretical basis for future studies on the mechanisms of SiNP-induced lung toxicity.

Opportunities and Challenges for Inhalable Nanomedicine Formulations in Respiratory Diseases: A Review

Lungs experience frequent interactions with the external environment and have an abundant supply of blood; therefore, they are susceptible to invasion by pathogenic microorganisms and tumor cells. However, the limited pharmacokinetics of conventional drugs in the lungs poses a clinical challenge. The emergence of different nano-formulations has been facilitated by advancements in nanotechnology. Inhaled nanomedicines exhibit better targeting and prolonged therapeutic effects. Although nano-formulations have great potential, they still present several unknown risks. Herein, we review the (1) physiological anatomy of the lungs and their biological barriers, (2) pharmacokinetics and toxicology of nanomaterial formulations in the lungs; (3) current nanomaterials that can be applied to the respiratory system and related design strategies, and (4) current applications of inhaled nanomaterials in treating respiratory disorders, vaccine design, and imaging detection based on the characteristics of different nanomaterials. Finally, (5) we analyze and summarize the challenges and prospects of nanomaterials for respiratory disease applications. We believe that nanomaterials, particularly inhaled nano-formulations, have excellent prospects for application in respiratory diseases. However, we emphasize that the simultaneous toxic side effects of biological nanomaterials must be considered during the application of these emerging medicines. This study aims to offer comprehensive guidelines and valuable insights for conducting research on nanomaterials in the domain of the respiratory system.

Lipidomics Investigation Reveals the Reversibility of Hepatic Injury by Silica Nanoparticles in Rats After a 6-Week Recovery Duration

Given the inevitable human exposure owing to its increasing production and utilization, the comprehensive safety evaluation of silica nanoparticles (SiNPs) has sparked concerns. Substantial evidence indicated liver damage by inhaled SiNPs. Notwithstanding, few reports focused on the persistence or reversibility of hepatic injuries, and the intricate molecular mechanisms involved remain limited. Here, rats are intratracheally instilled with SiNPs in two regimens (a 3-month exposure and a subsequent 6-week recovery after terminating SiNPs administration) to assess the hepatic effects. Nontargeted lipidomics revealed alterations in lipid metabolites as a contributor to the hepatic response and recovery effects of SiNPs. In line with the functional analysis of differential lipid metabolites, SiNPs activated oxidative stress, and induced lipid peroxidation and lipid deposition in the liver, as evidenced by the elevated hepatic levels of ROS, MDA, TC, and TG. Of note, these indicators showed great improvements after a 6-week recovery, even returning to the control levels. According to the correlation, ROC curve, and SEM analysis, 11 lipids identified as potential regulatory molecules for ameliorating liver injury by SiNPs. Collectively, the work first revealed the reversibility of SiNP-elicited hepatotoxicity from the perspective of lipidomics and offered valuable laboratory evidence and therapeutic strategy to facilitate nanosafety.

Adverse effects of cigarette filter silica on lungs: Comparison with natural crystalline silica particles

As a common additive in cigarette filters, nanosilica has been implemented to reduce the release of harmful substances in cigarette smoke. However, the potential risk of occupational exposure for cigarette factory workers is unknown. We collected physical examination data from 710 cigarette factory workers to evaluate the adverse effects of cigarette filter silica exposure. We also established mouse models induced by cigarette filter silica and crystalline silica separately to compare the lung inflammation, pulmonary function, apoptosis, and fibrosis of the two models. Workers in the rolling and packing workshop exposed to cigarette filter silica had a higher rate of abnormal lung function (17.75%) than those in the cutting workshop (0.87%). Animal experiments showed that compared with the same dose of crystalline silica, cigarette filter silica resulted in higher levels of inflammatory factors in the bronchoalveolar lavage fluid (BALF) of mice at day 7, and lower levels of total lung capacity (TLC), inspiratory capacity (IC), vital capacity (VC), and forced vital capacity (FVC) in mice at day 28. Additionally, both exposed groups of mice showed increased levels of caspase 3, collagen I (Col-Ⅰ), α-smooth muscle actin (α-SMA) and hydroxyproline (HYP) in the lungs, as well as collagen accumulation and fibrous nodules at day 28, with no significant difference between the two groups. The results suggested that cigarette filter silica caused more severe early lung inflammation and late ventilation impairment than the same dose of crystalline silica. In the future, we need to pay more attention to nanosilica protection in cigarette factories to prevent pulmonary dysfunction in workers.

C5a/C5aR1 axis as a key driver promotes epithelial-to-mesenchymal transition in airway epithelial cells in silica nanoparticles-induced pulmonary fibrosis

Previous studies have shown that silica nanoparticles (SiNPs) exposure can affect the respiratory, cardiovascular, reproductive and other systems, with the lung being the primary target organ for the direct effect, causing damage with a central feature of pulmonary inflammation and fibrosis. However, the underlying mechanisms of pulmonary fibrosis due to SiNPs are not fully understood. The aim of the study was to investigate the role of complement anaphylatoxin C5a in SiNPs-induced pulmonary fibrosis. A mouse model of SiNPs-induced pulmonary fibrosis was established, and pulmonary fibrosis-related indicators, epithelial-to-mesenchymal transition (EMT), C5a/C5aR1 and high mobility group protein B1 (HMGB1) proteins were measured. An in vitro study using the human lung epithelial cell line BEAS-2B investigated whether C5a leads to epithelial-to-mesenchymal trans-differentiation. In vivo studies revealed that SiNPs-induced pulmonary fibrosis mainly manifested as EMT trans-differentiation in airway epithelial cells, which subsequently led to excessive deposition of extracellular matrix (ECM). Furthermore, we found that C5a and C5aR1 proteins were also increased in SiNPs-induced pulmonary fibrosis tissue. In vitro studies also showed that C5a directly activated HMGB1/RAGE signaling and induced EMT in BEAS-2B cells. Finally, treatment of SiNPs-exposed mice with the C5aR1 inhibitor PMX205 effectively reduced C5aR1 levels and inhibited the activation of HMGB1/RAGE signaling and the expression of EMT-related proteins, culminating in a significant alleviation of pulmonary fibrosis. Taken together, our results suggest that C5a/C5aR1 is the main signaling pathway for SiNPs-induced pulmonary fibrosis, which induces EMT in airway epithelial cells via the HMGB1/RAGE axis.

Wnt5a/Ca2+ signaling regulates silica-induced ferroptosis in mouse macrophages by altering ER stress-mediated redox balance

Silicosis is a chronic pulmonary disease characterized by diffuse fibrosis of lung caused by the deposition of silica dust (SiO₂). The inhaled silica-induced oxidative stress, ROS production and macrophage ferroptosis are key drivers of the pathological process of silicosis. However, mechanisms that involved in the silica-induced macrophage ferroptosis and its contributions to pathogenesis of silicosis remain elusive. In the present study, we showed that silica induced murine macrophage ferroptosis, accompanied by elevation of inflammatory responses, Wnt5a/Ca²⁺ signaling activation, and concurrent increase of endoplasmic reticulum (ER) stress and mitochondrial redox imbalance in vitro and vivo. Mechanistic study further demonstrated that Wnt5a/Ca²⁺ signaling played a key role in silica-induced macrophage ferroptosis by modulating ER stress and mitochondrial redox balance. The presence of Wnt5a/Ca²⁺ signaling ligand Wnt5a protein increased the silica-induced macrophage ferroptosis by activating ER-mediated immunoglobulin heavy chain binding protein (Bip)-C/EBP homology protein (Chop) signaling cascade, reducing the expression of negative regulators of ferroptosis, glutathione peroxidase 4 (Gpx4) and solute carrier family 7 member 11 (Slc7a11), subsequentially increasing lipid peroxidation. The pharmacologic inhibition of Wnt5a signaling or block of calcium flow exhibited an opposite effect to Wnt5a, resulted in the reduction of ferroptosis and the expression of Bip-Chop signaling molecules. These findings were further corroborated by the addition of ferroptosis activator Erastin or inhibitor ferrostatin-1. These results provide a mechanism by which silica activates Wnt5a/Ca²⁺ signaling and ER stress, sequentially leads to redox imbalance and ferroptosis in mouse macrophage cells.

Silica nanoparticles aggravated the metabolic associated fatty liver disease through disturbed amino acid and lipid metabolisms-mediated oxidative stress

The metabolic associated fatty liver disease (MAFLD) is a public health challenge, leading to a global increase in chronic liver disease. The respiratory exposure of silica nanoparticles (SiNPs) has revealed to induce hepatotoxicity. However, its role in the pathogenesis and progression of MAFLD was severely under-studied. In this context, the hepatic impacts of SiNPs were investigated in vivo and in vitro through using ApoE^-/- mice and free fatty acid (FFA)-treated L02 hepatocytes. Histopathological examinations and biochemical analysis showed SiNPs exposure via intratracheal instillation aggravated hepatic steatosis, lipid vacuolation, inflammatory infiltration and even collagen deposition in ApoE^-/- mice, companied with increased hepatic ALT, AST and LDH levels. The enhanced fatty acid synthesis and inhibited fatty acid β-oxidation and lipid efflux may account for the increased hepatic TC/TG by SiNPs. Consistently, SiNPs induced lipid deposition and elevated TC in FFA-treated L02 cells. Further, the activation of hepatic oxidative stress was detected in vivo and in vitro, as evidenced by ROS accumulation, elevated MDA, declined GSH/GSSG and down-regulated Nrf2 signaling. Endoplasmic reticulum (ER) stress was also triggered in response to SiNPs-induced lipid accumulation, as reflecting by the remarkable ER expansion and increased BIP expression. More importantly, an UPLC-MS-based metabolomics analysis revealed that SiNPs disturbed the hepatic metabolic profile in ApoE^-/- mice, prominently on amino acids and lipid metabolisms. In particular, the identified differential metabolites were strongly correlated to the activation of oxidative stress and ensuing hepatic TC/TG accumulation and liver injuries, contributing to the progression of liver diseases. Taken together, our study showed SiNPs promoted hepatic steatosis and liver damage, resulting in the aggravation of MAFLD progression. More importantly, the disturbed amino acids and lipid metabolisms-mediated oxidative stress was a key contributor to this phenomenon from a metabolic perspective.