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

Our plain-English summary of Respirable stone particles differ in their ability to induce cytotoxicity and pro-inflammatory responses in cell models of the human airways, by V.S. Grytting, M. Refsnes, J. Øvrevik, et al (Particle and Fibre Toxicology, 2021).

The study

• Authors: V.S. Grytting, M. Refsnes, J. Øvrevik, M.S. Halle, J. Schönenberger, R. van der Lelij, B. Snilsberg, T. Skuland, R. Blom, M. Låg
• Journal: Particle and Fibre Toxicology
• Published: 2021;18(1):18
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

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.

In plain English

This was a laboratory study using human cells grown in dishes, not a study of people. The authors tested six samples of fine stone dust, mostly particles under 10 micrometres, from Norwegian stone quarries: quartzite, anorthosite, rhomb porphyry, dacite, quartz diorite and hornfels. A pure α-quartz sample was included for comparison. Asbestos was not tested. Human bronchial epithelial cells (HBEC3-KT), THP-1 macrophages and a mixed culture of both were exposed to 0–400 μg/mL of each dust for 24 hours. In the epithelial cells, quartzite and anorthosite were the most damaging stone samples and caused the most release of inflammatory signalling proteins (cytokines). In macrophages, quartzite and anorthosite were the most damaging, while anorthosite and hornfels caused the most cytokine release. The mixed culture showed few significant differences between samples. The stone dusts caused little bursting of donor red blood cells. A drug that blocks NLRP3, a protein that forms part of an inflammation-signalling complex called the NLRP3 inflammasome, reduced cytokine release in macrophages but not in epithelial cells. The authors concluded that the stone dusts caused cell damage and inflammatory responses, some as much as α-quartz or more. They added that there is currently no evidence these dusts cause the scarring or cancer seen with quartz and asbestos.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: In vitro (cell culture) experiment comparing stone particle samples in human airway cell models
• Who was studied: Human bronchial epithelial cells (HBEC3-KT), THP-1-derived macrophages, and a co-culture of the two. Human erythrocytes (red blood cells) from donors were used for a hemolysis test. The stone samples came from Norwegian stone quarries.
• Exposure: Six stone particle samples with diameter below 10 μm (quartzite, anorthosite, rhomb porphyry, dacite, quartz diorite, hornfels) plus a pure α-quartz reference sample (Min-U-Sil 5), at 0–400 μg/mL for 24 h. No asbestos was tested.
• Main results:
  • In HBEC3-KT epithelial cells, quartzite and anorthosite were the most cytotoxic stone samples and induced the highest cytokine levels.
  • In THP-1 macrophages, quartzite and anorthosite were the most cytotoxic samples, while anorthosite and hornfels induced the highest cytokine responses.
  • In the co-culture of epithelial cells and macrophages, few significant differences between particle samples were detected.
  • Adjusting for differences in particle surface area did not fully account for the differences between samples.
  • The stone particles had low hemolytic potential. Quartzite and anorthosite caused approximately 10% hemolysis at the highest concentration, compared with approximately 30% for α-quartz.
  • Pre-treatment with an NLRP3-specific inhibitor (MCC950) reduced stone particle-induced cytokine responses in THP-1 macrophages but not in HBEC3-KT cells.
  • Endotoxin levels in the particle samples were low, below 0.15 EU/mg.
• The authors' conclusion: The authors concluded that stone particles induce cytotoxicity and pro-inflammatory responses in human bronchial epithelial cells and macrophages, through NLRP3-independent and NLRP3-dependent mechanisms respectively. They found that some samples matched or exceeded α-quartz, and said these minerals warrant further attention. They also stated there is currently no evidence that these stone particles can cause the fibrotic and carcinogenic effects seen for quartz and asbestos.
• Limitations the authors state:
  • The particles bound cytokines in the medium used for the epithelial cells, so the potency of the stone samples relative to quartz may have been underestimated in HBEC3-KT cells.
  • Other injury-related mediators (HMGB1, IL-33, ATP) were not measured, so their involvement cannot be excluded.
  • The hemolysis assay may not predict lysosomal rupture caused by stone particles.

Topics

Medical terms in this study, explained in our Lexicon: Macrophage, Cytokine.

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