Quartz Disrupts Iron Homeostasis in Alveolar Macrophages To Impact a Pro-Inflammatory Effect

Mucus increases cell iron uptake to impact the release of pro-inflammatory mediators after particle exposure

We tested the hypothesis that (1) mucus production can be included in the cell response to iron deficiency; (2) mucus binds iron and increases cell metal uptake; and subsequently (3) mucus impacts the inflammatory response to particle exposure. Using quantitative PCR, RNA for both MUC5B and MUC5AC in normal human bronchial epithelial (NHBE) cells decreased following exposures to ferric ammonium citrate (FAC). Incubation of mucus-containing material collected from the apical surface of NHBE cells grown at air-liquid interface (NHBE-MUC) and a commercially available mucin from porcine stomach (PORC-MUC) with iron demonstrated an in vitro capacity to bind metal. Inclusion of either NHBE-MUC or PORC-MUC in incubations of both BEAS-2B cells and THP1 cells increased iron uptake. Exposure to sugar acids (N-acetyl neuraminic acid, sodium alginate, sodium guluronate, and sodium hyaluronate) similarly increased cell iron uptake. Finally, increased metal transport associated with mucus was associated with a decreased release of interleukin-6 and -8, an anti-inflammatory effect, following silica exposure. We conclude that mucus production can be involved in the response to a functional iron deficiency following particle exposure and mucus can bind metal, increase cell uptake to subsequently diminish or reverse a functional iron deficiency and inflammatory response following particle exposure.

Iron Deficiency and Overload Modulate the Inflammatory Responses and Metabolism of Alveolar Macrophages

Alveolar macrophages (AM) are critical to defense against respiratory pathogens. This study evaluated cellular iron imbalance to immunometabolism in endotoxin-polarized porcine AMs (PAMs). PAMs collected from five 6-week-old pigs were treated with a basal media, iron chelator, or ferric ammonium citrate to maintain iron replete or induce iron deficiency or overload, respectively. After 24 h treatment, PAMs were challenged with saline or lipopolysaccharide (LPS) for 6 h. Cells were analyzed for gene, protein, and untargeted metabolome. Cytokines were determined in culture media. Data were assessed using two-way ANOVA. Treatments successfully induced iron deficiency and overload. The mRNA of DMT1 and ZIP14 was increased up to 300-fold by LPS, but unaffected by iron. Surprisingly, both iron deprivation and overload attenuated LPS-induced inflammation, showing less TNFα production and lower mRNA of pro- and anti-inflammatory cytokines than iron-replete PAMs. Forty-eight metabolites were altered by either or both main effects. LPS enhanced the glycolysis and polyol pathways. Iron deprivation disrupted the TCA cycle. Iron overload increased intracellular cholesterol. Interestingly, iron deprivation augmented, whereas iron overload diminished, LPS-induced itaconic acid production, which has anti-microbial and anti-inflammatory properties. Therefore, iron-deficient PAMs may be more resistant to intracellular pathogens which use PAMs as a conduit for infection.

The influence of exposure approaches to in vitro lung epithelial barrier models to assess engineered nanomaterial hazard

Exposure to engineered nanomaterials (ENM) poses a potential health risk to humans through long-term, repetitive low-dose exposures. Currently, this is not commonplace within in vitro lung cell cultures. Therefore, the purpose of this study was to consider the optimal exposure approach toward determining the stability, sensitivity and validity of using in vitro lung cell mono- and co-cultures to determine ENM hazard. A range of exposure scenarios were conducted with DQ₁₂ (previously established as a positive particle control) (historic and re-activated), TiO₂ (JRC NM-105) and BaSO₄ (JRC NM-220) on both monocultures of A549 cells as well as co-cultures of A549 cells and differentiated THP-1 cells. Cell cultures were exposed to either a single, or a repeated exposure over 24, 48- or 72-hours at in vivo extrapolated concentrations of 0-5.2 µg/cm², 0-6 µg/cm² and 0-1µg/cm². The focus of this study was the pro-inflammatory, cytotoxic and genotoxic response elicited by these ENMs. Exposure to DQ₁₂ caused pro-inflammatory responses after 48 hours repeat exposures, as well as increases in micronucleus frequency. Neither TiO₂ nor BaSO₄ elicited a pro-inflammatory response at this time point. However, there was induction of IL-6 after 24 hours TiO₂ exposure. In conclusion, it is important to consider the appropriateness of the positive control implemented, the cell culture model, the time of exposure as well as the type of exposure (bolus or fractionated) before establishing if an in vitro model is appropriate to determine the level of response to the specific ENM of interest.

Cigarette Smoke Particle-Induced Lung Injury and Iron Homeostasis

It is proposed that the mechanistic basis for non-neoplastic lung injury with cigarette smoking is a disruption of iron homeostasis in cells after exposure to cigarette smoke particle (CSP). Following the complexation and sequestration of intracellular iron by CSP, the host response (eg, inflammation, mucus production, and fibrosis) attempts to reverse a functional metal deficiency. Clinical manifestations of this response can present as respiratory bronchiolitis, desquamative interstitial pneumonitis, pulmonary Langerhans’ cell histiocytosis, asthma, pulmonary hypertension, chronic bronchitis, and pulmonary fibrosis. If the response is unsuccessful, the functional deficiency of iron progresses to irreversible cell death evident in emphysema and bronchiectasis. The subsequent clinical and pathological presentation is a continuum of lung injuries, which overlap and coexist with one another. Designating these non-neoplastic lung injuries after smoking as distinct disease processes fails to recognize shared relationships to each other and ultimately to CSP, as well as the common mechanistic pathway (ie, disruption of iron homeostasis).

Diacetyl exposure disrupts iron homeostasis in animals and cells

OBJECTIVE

Several mechanisms have been proposed for the biological effect of diacetyl. We tested the postulate that animal and cell exposures to diacetyl are associated with a disruption in iron homeostasis.

MATERIALS AND METHODS

Male, Sprague-Dawley rats were intratracheally-instilled with either distilled water or diacetyl. Seven days after treatment, animals were euthanized and the lungs removed, fixed, and embedded. Sections were cut and stained for iron, collagen, and ferritin. Human epithelial (BEAS-2B) and monocytic (THP-1) cells were exposed in vitro to ferric ammonium citrate (FAC), diacetyl, and both FAC and diacetyl. Cell non-heme iron concentrations and ferritin levels were quantified using inductively coupled plasma optical emission spectroscopy and an immunoassay respectively.

RESULTS

After exposure of animals to diacetyl, there were airway polypoid lesions which stained positively for both iron and the intracellular storage protein ferritin. Trichrome stain showed a deposition of collagen immediately adjacent to accumulated metal following diacetyl exposure. In in vitro cell exposures, FAC increased non-heme iron concentration but co-incubations of FAC and diacetyl elevated levels to significantly greater values. Levels of ferritin were increased with exposures of BEAS-2B and THP-1 cells to FAC but were similarly greater after co-exposure with FAC and diacetyl.

CONCLUSIONS

Results of animal and cell studies support a disruption of iron homeostasis by diacetyl. It is proposed that, following internalization, diacetyl complexes intracellular sources of iron. The cell recognizes a loss of its requisite iron to diacetyl and imports greater concentrations of the metal.

Silica nanoparticle induces pulmonary fibroblast transdifferentiation via macrophage route: Potential mechanism revealed by proteomic analysis

Recently, more and more attention has been focused on silica nanoparticles (SiNPs) as they are increasingly used in various fields. Yet, their biological effects, especially on human beings, largely remain unknown. This study was implanted to assess the biological responses in vitro elicited by human macrophages exposed to the SiNPs and to explore its toxicity and fibrosis biomarker. We found that SiNPs suppressed the viability of THP-1 cells in a dose-dependent manner while they triggered apoptosis and promoted the secretion of inflammatory factors. Next, SiNPs-induced macrophage supernatant was used to act on fibroblast (MRC-5), indicating that the expression of hydroxyproline (Hyp), α-SMA, and collagonIin MRC-5 increased after SiNPs treatment. To further explore the biomarker of fibrosis, Liquid-mass spectrometry facilitated quantitative proteomics, identified 3247 proteins, of which 791 proteins were expressed differentially in human embryonic lung fibroblasts after treated with SiNPs. In conclusion, our observations suggest that SiNPs induced THP-1-derived macrophage damage and apoptosis. Moreover, SiNPs induced macrophages to secrete cytokines that promote fibroblasts' proliferation and differentiation and changed protein expression in MRC-5 cells, regulating biological processes such as apoptosis, protein synthesis, and cell growth. Among these results, our findings could provide a basis for determining fibrosis biomarkers of silica nanoparticle exposure.

Rapid Induction of Pulmonary Inflammation, Autoimmune Gene Expression, and Ectopic Lymphoid Neogenesis Following Acute Silica Exposure in Lupus-Prone Mice

Occupational exposure to crystalline silica (cSiO2) is etiologically associated with systemic lupus erythematosus (lupus) and other autoimmune diseases. cSiO2's autoimmune effects in humans can be mimicked chronically in female lupus-prone NZBWF1 mice following repeated exposure to the particle. However, the immediate and short-term effects of cSiO2 in this widely used model of autoimmune disease are not well-understood. In the present study, we tested the hypothesis that a single acute cSiO2 dose triggers early presentation of cellular, histopathological, transcriptomic, and protein biomarkers of inflammation and autoimmunity in lupus-prone mice. Eight-week old female NZBWF1 mice were intranasally instilled once with 2.5 mg cSiO2 or saline vehicle and necropsied at 1, 7, 14, 21, and 28 d post-instillation (PI). Analyses of bronchoalveolar lavage fluid (BALF) and lung tissue revealed that by 7 d PI, acute cSiO2 exposure persistently provoked: (i) robust recruitment of macrophages, neutrophils, and lymphocytes into the alveoli, (ii) cell death as reflected by increased protein, double-stranded DNA, and lactate dehydrogenase activity, (iii) elevated secretion of the cytokines IL-1α, IL-1β, IL-18, TNF-α, IL-6, MCP-1, and B cell activation factor (BAFF), and (iv) upregulation of genes associated with chemokines, proinflammatory cytokines, lymphocyte activation, and type I interferon signaling. The appearance of these endpoints was subsequently followed by the emergence in the lung of organized CD3+ T cells (14 d PI) and CD45R+ B cells (21 d PI) that were indicative of ectopic lymphoid structure (ELS) development. Taken together, acute cSiO2 exposure triggered a rapid onset of autoimmune disease pathogenesis that was heralded in the lung by unresolved inflammation and cell death, proinflammatory cytokine production, chemokine-driven recruitment of leukocytes, an interferon response signature, B and T cell activation, and ELS neogenesis. This short-term murine model provides valuable new insight into potential early mechanisms of cSiO2-induced lupus flaring and, furthermore, offers a rapid venue for evaluating interventions against respirable particle-triggered inflammation and autoimmunity.

Silica dust exposure induces autophagy in alveolar macrophages through switching Beclin1 affinity from Bcl-2 to PIK3C3

Increased deposition of silica dust in pulmonary interstitial tissues leads to silicosis, in which autophagy plays a defensive role in silica dust-associated stress response and cell death. Our previous studies revealed that silica dust exposure contributed to autophagy in pulmonary macrophages in vivo, while the specific regulatory mechanism is still unclear. This study aimed to figure out the regulatory mechanism as well as the role of autophagy in the pathogenesis of experimental silicosis. We used 3-methyladenine (3-MA) and ABT-737 to suppress the expression of phosphatidylinositol 3-kinase catalytic subunit type 3 (PIK3C3) and B cell leukemia/lymphoma 2 (Bcl-2), two critical initiators of autophagy, and detected and evaluated the autophagy in NR8383 cells with or without silica dust exposure. We found that exposure of silica dust increased autophagy in NR8383 cells and elevated the expression of Beclin1 and PIK3C3, but it reduced the expression of Bcl-2. The relationship among Beclin1, PIK3C3, and Bcl-2 were then investigated using immunoprecipitation analysis, and we found that suppression of PIK3C3 and/or Bcl-2 using 3-MA and/or ABT-737 could alter the autophagy induced by silica dust in NR8383 cells, and the complexes of Beclin1/PIK3C3 and Beclin1/Bcl-2 were both downregulated, which may be that inhibition of PIK3C3 and Bcl-2 altered the affinity of Beclin1 with PIK3C3 and Bcl-2 and lead to the silence of PIK3C3 signaling. These findings indicate that silica dust exposure induces autophagy via changing the connectivity of Beclin1 from Bcl-2 to PIK3C3.