In vitro determinants of asbestos fiber toxicity: effect on the relative toxicity of Libby amphibole in primary human airway epithelial cells

Our plain-English summary of In vitro determinants of asbestos fiber toxicity: effect on the relative toxicity of Libby amphibole in primary human airway epithelial cells, by K.E. Duncan, P.M. Cook, S.H. Gavett, et al (Particle and Fibre Toxicology, 2014).

The study

• Authors: K.E. Duncan, P.M. Cook, S.H. Gavett, L.A. Dailey, R.K. Mahoney, A.J. Ghio, V.L. Roggli, R.B. Devlin
• Journal: Particle and Fibre Toxicology
• Published: 2014;11:2
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: An abnormally high incidence of lung disease has been observed in the residents of Libby, Montana, which has been attributed to occupational and environmental exposure to fibrous amphiboles originating from a nearby contaminated vermiculite mine. The composition of Libby amphibole (LA) is complex and minimal toxicity data are available. In this study, we conduct a comparative particle toxicity analysis of LA compared with standard reference asbestiform amphibole samples.

Methods: Primary human airway epithelial cells (HAEC) were exposed to two different LA samples as well as standard amphibole reference samples. Analysis of the samples included a complete particle size distribution analysis, calculation of surface area by electron microscopy and by gas adsorption and quantification of surface-conjugated iron and hydroxyl radical production by the fibers. Interleukin-8 mRNA levels were quantified by qRT-PCR to measure relative pro-inflammatory response induced in HAEC in response to amphibole fiber exposure. The relative contribution of key physicochemical determinants on the observed pro-inflammatory response were also evaluated.

Results: The RTI amosite reference sample contained the longest fibers and demonstrated the greatest potency at increasing IL-8 transcript levels when evaluated on an equal mass basis. The two LA samples and the UICC amosite reference sample consisted of similar particle numbers per milligram as well as similar particle size distributions and induced comparable levels of IL-8 mRNA. A strong correlation was observed between the elongated particle (aspect ratio ≥3:1) dose metrics of length and external surface area. Expression of the IL-8 data with respect to either of these metrics eliminated the differential response between the RTI amosite sample and the other samples that was observed when HAEC were exposed on an equal mass basis.

Conclusions: On an equal mass basis, LA is as potent as the UICC amosite reference sample at inducing a pro-inflammatory response in HAEC but is less potent than the RTI amosite sample. The results of this study show that the particle length and particle surface area are highly correlated metrics that contribute significantly to the toxicological potential of these amphibole samples with respect to the inflammogenic response induced in airway epithelial cells.

In plain English

This laboratory study compared two Libby amphibole samples (LA2000 and LA2007, collected near Libby, Montana in 2000 and 2007) with two reference amosite samples (RTI and UICC). Primary human airway epithelial cells, taken by brush biopsy from healthy non-smoking volunteers, were exposed for 24 hours to 2.64, 13.2 or 26.4 micrograms per square centimetre of each sample, and messenger RNA for IL-8, IL-6, TNF and COX-2 was measured. The samples were also characterised for particle size distribution, particle number, surface area, surface iron and hydroxyl radical production. On an equal mass basis the two higher doses raised all four transcripts significantly (p less than 0.05); IL-8 rose 40 to 50 fold for the Libby samples at the highest dose. The RTI amosite sample, which had the longest particles and about ten-fold fewer particles per milligram, produced the largest IL-8 response. The authors concluded that, per unit mass, Libby amphibole was as potent as UICC amosite but less potent than RTI amosite, and that elongated particle length and surface area, which were highly correlated, contributed substantially to the response.

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 comparative particle toxicity experiment in cultured primary human cells, with physicochemical characterisation of the mineral samples
• Who was studied: Primary human airway epithelial cells (HAEC) obtained by brush biopsy of the mainstem bronchus of healthy, non-smoking adult volunteers; three biological replicates (cells from three different donors), nine exposure replicates per condition
• Exposure: Libby amphibole samples LA2000 and LA2007 (from the Rainy Creek Complex near Libby, Montana) and two reference amosite samples (RTI and UICC), at 2.64, 13.2 or 26.4 micrograms per square centimetre for 24 hours
• Main results:
  • Particle numbers per milligram were similar for LA2000 (98.2 x10^7), LA2007 (103 x10^7) and UICC amosite (94.2 x10^7), while RTI amosite had about ten-fold fewer (9.15 x10^7)
  • Mean length of elongated mineral particles (aspect ratio 3:1 or greater) was 12.1 ± 1.2 micrometres for RTI amosite versus 4.4 ± 0.2 (LA2000), 3.8 ± 0.3 (LA2007) and 4.3 ± 0.5 (UICC amosite)
  • Cytotoxicity at the highest dose (26.4 micrograms per square centimetre) was mild: 3.9% LDH release in unexposed controls versus 8% to 10% in exposed cells, significant versus control but with no significant difference between amphibole samples
  • On an equal mass basis, both Libby amphibole samples raised transcripts 4-5 fold for COX-2 up to 40-50 fold for IL-8 at 26.4 micrograms per square centimetre, with no significant difference between the two LA samples or between LA and UICC amosite
  • RTI amosite was the most potent sample on an equal mass basis for IL-8, IL-6 and COX-2 relative to the Libby samples, and for IL-8 relative to UICC amosite
  • The sum-of-lengths dose for elongated mineral particles was highly correlated with their surface area measured by TEM (r = 0.94)
  • Both amosite reference samples had significantly greater ionizable iron than the two LA samples, and produced greater quantities of hydroxyl radical, a trend that did not follow the IL-8 response
• The authors' conclusion: The authors concluded that Libby amphibole was as potent as UICC amosite, but less potent than RTI amosite, at inducing a pro-inflammatory response in lung epithelial cells on an equal mass basis, and that surface area and sum of particle lengths of elongated mineral particles are correlated metrics contributing significantly to the pathogenic potential of these fibres
• Limitations the authors state:
  • Gas adsorption surface area measurement does not distinguish amphibole from non-amphibole particles or fibrous from non-fibrous particles
  • Surface area calculated by electron microscopy is less precise at detecting surface irregularities
  • No statistical testing was done on the IL-8 data re-expressed by the alternative dose metrics
  • The effect of particle length on the acute pro-inflammatory response in airway epithelial cells is not well established, and other cell types and endpoints were not examined

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Libby vermiculite mine, Montana

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: Libby amphiboles, Environmental Exposure, Amphibole Group, vermiculite, Asbestiform, Hydroxyl Radical, Amosite, UICC.

Related studies

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• Acute effects of multi-walled carbon nanotubes on primary bronchial epithelial cells from COPD patients — S. Beyeler, S. Chortarea, et al. (2018)
• Cyto-genotoxicity of amphibole asbestos fibers in cultured human lung epithelial cell line: role of surface iron — R.K. Srivastava, M. Lohani, et al. (2010)
• Libby amphibole-induced mesothelial cell autoantibodies promote collagen deposition in mice — J. Gilmer, K. Serve, et al. (2016)
• Neoplastic-like transformation effect of single-walled and multi-walled carbon nanotubes compared to asbestos on human lung small airway epithelial cells — L. Wang, T.A. Stueckle, et al. (2014)
• Modulation of DNA single-strand breaks by intracellular glutathione in human lung cells exposed to asbestos fibers — A. Puhakka, T. Ollikainen, et al. (2002)

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