Biological response of an in vitro human 3D lung cell model exposed to brake wear debris varies based on brake pad formulation

Our plain-English summary of Biological response of an in vitro human 3D lung cell model exposed to brake wear debris varies based on brake pad formulation, by H. Barosova, S. Chortarea, P. Peikertova, et al (Archives of Toxicology, 2018).

The study

• Authors: H. Barosova, S. Chortarea, P. Peikertova, M.J.D. Clift, A. Petri-Fink, J. Kukutschova, B. Rothen-Rutishauser
• Journal: Archives of Toxicology
• Published: 2018;92(7):2339-2351
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Wear particles from automotive friction brake pads of various sizes, morphology, and chemical composition are significant contributors towards particulate matter. Knowledge concerning the potential adverse effects following inhalation exposure to brake wear debris is limited. Our aim was, therefore, to generate brake wear particles released from commercial low-metallic and non-asbestos organic automotive brake pads used in mid-size passenger cars by a full-scale brake dynamometer with an environmental chamber simulating urban driving and to deduce their potential hazard in vitro. The collected fractions were analysed using scanning electron microscopy via energy-dispersive X-ray spectroscopy (SEM-EDS) and Raman microspectroscopy. The biological impact of the samples was investigated using a human 3D multicellular model consisting of human epithelial cells (A549) and human primary immune cells (macrophages and dendritic cells) mimicking the human epithelial tissue barrier. The viability, morphology, oxidative stress, and (pro-)inflammatory response of the cells were assessed following 24 h exposure to ~ 12, ~ 24, and ~ 48 µg/cm2 of non-airborne samples and to ~ 3.7 µg/cm2 of different brake wear size fractions (2-4, 1-2, and 0.25-1 µm) applying a pseudo-air-liquid interface approach. Brake wear debris with low-metallic formula does not induce any adverse biological effects to the in vitro lung multicellular model. Brake wear particles from non-asbestos organic formulated pads, however, induced increased (pro-)inflammatory mediator release from the same in vitro system. The latter finding can be attributed to the different particle compositions, specifically the presence of anatase.

In plain English

This laboratory study tested particles worn off commercial car brake pads on human lung cells grown in culture. The authors made wear debris on a full-scale brake dynamometer that simulated urban driving, using 'low-metallic' and 'non-asbestos organic' (NAO) pads. The article does not state whether the low-metallic pads contained asbestos. For 24 hours they applied debris to a 3D model combining A549 lung epithelial cells with human immune cells: settled debris from each pad type at about 12, 24 and 48 µg/cm2, and three airborne size fractions from the low-metallic pads at about 3.7 µg/cm2. They ran three independent experiments. Low-metallic debris did not change cell shape. No sample significantly changed oxidative stress. NAO debris significantly increased release of the inflammatory signal IL-8 at all concentrations and changed the cells' structure. It also slightly increased cell death, but this was not statistically significant. The NAO debris contained anatase, a form of titanium dioxide, to which the authors attributed this response. They noted that cells were exposed only once and the findings do not represent all brake materials or braking scenarios.

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 laboratory experiment: brake wear particles generated on a full-scale brake dynamometer, chemically characterised, then applied to a 3D human lung cell co-culture model
• Who was studied: A 3D co-culture of human A549 alveolar epithelial type-II cells with primary human blood monocyte-derived macrophages and dendritic cells (from blood buffy coats, Bern University hospital, Switzerland); three independent experiments for all endpoints
• Exposure: Brake wear debris from commercial low-metallic pads (below 3 wt% metallic components) and non-asbestos organic (NAO) pads. Non-airborne debris from both pad types was applied at 2, 1 and 0.5 mg/mL (about 48, 24 and 12 µg/cm2). Airborne size fractions of low-metallic debris (2–4, 1–2 and 0.25–1 µm) were applied at 33 µg/mL (about 3.7 µg/cm2). All exposures lasted 24 hours and were applied as a thin liquid layer on the cell surface (pseudo-air-liquid interface). The article does not state whether the low-metallic pads contained asbestos.
• Main results:
  • IL-8 release increased significantly (p less than 0.05) after exposure to NAO debris at all concentrations.
  • No significant increase in IL-1β or TNF-α production was observed.
  • No sample significantly changed oxidative stress (total glutathione) in any cell culture (p greater than 0.05).
  • NAO debris produced a slight increase in cell death compared with the low-metallic debris that was not statistically significant (p greater than 0.05).
  • Cells exposed to NAO debris showed changes in the cytoskeleton.
  • Cells exposed to the low-metallic samples (non-airborne and size fractions) showed no difference in shape from untreated cells.
  • The low-metallic size fractions, applied at about 3.7 µg/cm2 to represent realistic ambient conditions, caused no significant changes in any response measured.
  • Raman microspectroscopy detected anatase (titanium dioxide) in the NAO sample. The authors suggested the IL-8 increase from NAO debris could be related to titanium dioxide.
  • No endotoxin was detected in the non-airborne samples (below 0.5 EU/mL).
• The authors' conclusion: The authors concluded that low doses of the size fractions and the low-metallic brake wear particles did not activate a biological response in the lung cell model. They concluded that the non-asbestos organic sample caused a heightened (pro-)inflammatory response, which they attributed to the presence of anatase.
• Limitations the authors state:
  • Size fractions of the NAO debris could not be collected, so only non-airborne NAO debris was tested.
  • Cells were exposed only once, which reflects an acute exposure rather than repeated long-term exposure.
  • The concentration of the size fractions could not be increased because too little particle mass was collected.
  • The low doses used for the size fractions might have been too low to trigger a response.
  • The doses used for the non-airborne samples were too low to reach the upper limit of a lifetime worst-case scenario.
  • Raman microspectroscopy most likely cannot detect particles smaller than 500 nm.
  • Pad formulations are proprietary, so the original pads could not be compared with their wear debris.
  • The findings are not representative of all brake materials and braking scenarios.

Topics

Medical terms in this study, explained in our Lexicon: Brake Lining, Scanning Electron Microscopy (SEM), Macrophage, Oxidative Stress.

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