Respirable stone particles differ in their ability to induce cytotoxicity and pro-inflammatory responses in cell models of the human airways

Abstract

Background Respirable stone- and mineral particles may be a major constituent in occupational and ambient air pollution and represent a possible health hazard. However, with exception of quartz and asbestos, little is known about the toxic properties of mineral particles. In the present study, the pro-inflammatory and cytotoxic responses to six stone particle samples of different composition and with diameter below 10 μm were assessed in human bronchial epithelial cells (HBEC3-KT), THP-1 macrophages and a HBEC3-KT/THP-1 co-culture. Moreover, particle-induced lysis of human erythrocytes was assessed to determine the ability of the particles to lyse biological membranes. Finally, the role of the NLRP3 inflammasome was assessed using a NLRP3-specific inhibitor and detection of ASC oligomers and cleaved caspase-1 and IL-1β. A reference sample of pure α-quartz was included for comparison. Results Several stone particle samples induced a concentration-dependent increase in cytotoxicity and secretion of the pro-inflammatory cytokines CXCL8, IL-1α, IL-1β and TNFα. In HBEC3-KT, quartzite and anorthosite were the most cytotoxic stone particle samples and induced the highest levels of cytokines. Quartzite and anorthosite were also the most cytotoxic samples in THP-1 macrophages, while anorthosite and hornfels induced the highest cytokine responses. In comparison, few significant differences between particle samples were detected in the co-culture. Adjusting responses for differences in surface area concentrations did not fully account for the differences between particle samples. Moreover, the stone particles had low hemolytic potential, indicating that the effects were not driven by membrane lysis. Pre-incubation with a NLRP3-specific inhibitor reduced stone particle-induced cytokine responses in THP-1 macrophages, but not in HBEC3-KT cells, suggesting that the effects are mediated through different mechanisms in epithelial cells and macrophages. Particle exposure also induced an increase in ASC oligomers and cleaved caspase-1 and IL-1β in THP-1 macrophages, confirming the involvement of the NLRP3 inflammasome. Conclusions The present study indicates that stone particles induce cytotoxicity and pro-inflammatory responses in human bronchial epithelial cells and macrophages, acting through NLRP3-independent and -dependent mechanisms, respectively. Moreover, some particle samples induced cytotoxicity and cytokine release to a similar or greater extent than α-quartz. Thus, these minerals warrant further attention in future research.

The pro-inflammatory effects of combined exposure to diesel exhaust particles and mineral particles in human bronchial epithelial cells

“…As for α-quartz, exposure to anorthosite, rhomb porphyry or quartz diorite particles in combination with DEP B0 induced significant increases in the secretion of pro-inflammatory cytokines and expression of genes related to inflammation and redox responses compared with exposure to the individual particle samples. The potency of the mineral samples in combination with DEP B0 was mostly in line with the order of potency reported for the individual samples in previous studies using the same cell model, with α-quartz being the most potent followed by anorthosite, while rhomb porphyry and quartz diorite induced lower and similar levels [ 48 ]. Considering that the anorthosite does not contain any quartz (Additional file 3 : Table S1) [ 48 ], these results clearly show that the increased effects of combined exposure cannot be explained by quartz content alone, suggesting that other mineral components are important.…”

“…Based on these results, the concentrations of 25 and 50 µg/mL DEP (2.6 and 5.3 μg/cm 2 ) were chosen for the combination experiments. The concentrations of 25, 50 and 100 μg/mL α-quartz (2.6, 5.3 and 10.5 μg/cm 2 ) were chosen based on previous experiments published elsewhere [ 48 ]. A cytokine-binding assay was also performed to assess whether non-specific binding of cytokines to DEP may have interfered with the measurements [ 54 ].…”

“…Samples of anorthosite, rhomb porphyry and quartz diorite particles (< 10 μm) were derived from crushed stone material and consist of a mixture of different minerals, including feldspar, quartz, epidote, hornblende, calcite, chlorite and muscovite. The characteristics of the stone particle samples and their ability to induce cytotoxicity and pro-inflammatory cytokines have been described in a previous study using the same cell model as in the present study [ 48 ]. Moreover, the mineral composition of the samples is included in the online supplement of the current study (Additional file 3 : Table S1).…”

“…While other minerals have received less attention, previous studies from our group suggest that a variety of mineral particle samples can induce pro-inflammatory responses in vitro and in vivo, and that the potency of the particles differs between samples of different mineral composition [ 47 – 50 ]. Moreover, recent studies show that several mineral particle samples can induce cytotoxicity and cytokine release of the same magnitude as quartz in immune cells and bronchial epithelial cells in vitro [ 48 ]. Furthermore, studies using road wear simulators suggest that mineral-rich particles from asphalt composed of different stone materials also vary in their ability to induce cytokine release in macrophages [ 51 , 52 ], suggesting that the presence of different stone materials in asphalt may possibly confer different toxic properties to the resulting PM.…”

Silica Induction of Diverse Inflammatory Proteome in Lungs of Lupus-Prone Mice Quelled by Dietary Docosahexaenoic Acid Supplementation

“…IPA analysis indicated that IL-1, IL-6, and TNF-a were among the chief regulators for predicted pathways mediating cSiO 2triggered inflammatory proteins and that these pathways were downregulated by DHA. cSiO 2 instillation into the lung is wellknown to acutely elicit secretion of proinflammatory cytokines such as IL-1b, IL-1a, IL-6, and TNF-a by direct or indirect action on alveolar macrophages, neutrophils, and epithelial cells (40)(41)(42)(43). Therefore, it was surprising that cSiO 2 's effects on these proinflammatory cytokines in BALF were modest across the time cohorts of this study.…”