A new technique to examine individual pollutant particle and fibre deposition and transit behaviour in live mouse trachea

Our plain-English summary of A new technique to examine individual pollutant particle and fibre deposition and transit behaviour in live mouse trachea, by M. Donnelley, K.K. Siu, K.S. Morgan, et al (Journal of Synchrotron Radiation, 2010).

The study

• Authors: M. Donnelley, K.K. Siu, K.S. Morgan, W. Skinner, Y. Suzuki, A. Takeuchi, K. Uesugi, N. Yagi, D.W. Parsons
• Journal: Journal of Synchrotron Radiation
• Published: 2010;17(6):719-29
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

During respiration, particles suspended in the air are inhaled and unless cleared by airway defences they can remain and affect lung health. Their size precludes the use of standard imaging modalities so we have developed synchrotron phase-contrast X-ray imaging (PCXI) methods to non-invasively monitor the behaviour of individual particles in live mouse airways. In this study we used these techniques to examine post-deposition particle behaviour in the trachea. PCXI was used to monitor the deposition and subsequent behaviour of particles of quarry dust and lead ore; fibres of asbestos and fibreglass; and hollow glass micro-spheres. Visibility was examined in vitro and ex vivo to avoid the complicating effects of surrounding tissue and respiratory or cardiac motion. Particle behaviour was then examined after deposition onto the tracheal airway surfaces of live mice. Each particle and fibre looked and behaved differently on the airway surface. Particles lodged on the airway shortly after deposition, and the rate at which this occurred was dependent on the particle type and size. After the live-imaging experiments, excised airway samples were examined using light and electron microscopy. Evidence of particle capture into the airway surface fluids and the epithelial cell layer was found. PCXI is a valuable tool for examining post-deposition particulate behaviour in the tracheal airway. These first indications that the interaction between airways and individual particles may depend on the particle type and size should provide a novel approach to studying the early effects of respired particles on airway health.

In plain English

This animal experiment tested a new imaging method, synchrotron phase-contrast X-ray imaging, for watching individual pollutant particles and fibres in the windpipe (trachea) of live mice. The authors prepared chrysotile (white asbestos), fibreglass, galena (lead ore), dolomite quarry dust and hollow silver-coated glass beads. They delivered each in saline through a breathing tube to three of 15 anaesthetised hairless mice and imaged for about 42 minutes. Fibreglass, galena, quarry dust and the glass beads were detected in the live mice. Galena was the most visible and quarry dust the least. Most particle motion happened in the first few minutes, and large or dense particles lodged sooner than small or light ones. Asbestos fibres were not identified in the images or in tissue sections, and the authors speculated that the asbestos was not successfully delivered to the trachea. The authors reported clear differences in behaviour between particle types, but said their sample was too small to determine whether the types produced distinct patterns. The authors proposed the method as a valuable technique for studying pollutant particles in live animal airways.

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: Animal experiment (imaging method development) using synchrotron phase-contrast X-ray imaging, with laboratory tests of samples, a pilot study on one excised mouse trachea, imaging of live mice, and microscopy of the tracheas afterwards
• Who was studied: 15 hairless HOS:HR-1 mice weighing 18–26 g, in groups of three per particle type, imaged at the SPring-8 synchrotron facility in Japan. One further mouse was used for the excised-trachea pilot. The mice were not allowed to recover.
• Exposure: A single small saline bolus at 1% w/v of one of five materials, delivered through a tube into the trachea: chrysotile (white asbestos), fibreglass from pipe insulation, galena (lead sulfide ore), dolomite quarry dust, or hollow silver-coated glass beads used as reference particles
• Main results:
  • In live mice, asbestos fibres were not positively identified in any image sequence.
  • No asbestos fibres were found in tissue cross sections from the asbestos-treated mice. The authors speculated that the asbestos was not successfully delivered to the trachea, noting that asbestos fibres tended to cluster and block fine delivery tubes in bench tests.
  • Of the materials detected in live mice, galena was the most visible and quarry dust the least visible.
  • Most particle motion occurred in the first few minutes, and almost all particles had lodged by the end of imaging.
  • Small and/or low-density particles kept moving longer than large and/or dense particles, which lodged quickly on the airway surface.
  • The authors stated that, across the different particle and fibre types, all delivered under the same anaesthetic regime, there were clear differences in post-deposition transit behaviour.
  • Regardless of particle type and size, most deposition and motion occurred on the dorsal (back) side of the trachea.
  • Under light microscopy, all particle types except asbestos were found on or in the airway lining. Samples from the quarry-dust mice were processed incorrectly and could not be examined.
  • The estimated radiation dose was approximately 0.13 Gy per exposure to the imaged area in the live-mouse studies.
• The authors' conclusion: The authors proposed that phase-contrast X-ray imaging is a valuable technique for studying how pollutant particles and fibres deposit and behave in the airways of live animal models.
• Limitations the authors state:
  • The sample size was too small to determine whether different particle types produced distinct patterns of behaviour on the airway surface.
  • Particles of about 5 micrometres in diameter were the smallest that could be accurately detected and tracked.
  • The anaesthetics used may slow mucus clearance, so true transit rates are likely faster than those measured.
  • A delay of typically one minute between delivery and imaging meant the actual delivery of particles into the airway could not be seen.
  • The analysis was limited to the trachea and did not cover the airways inside the lungs.
  • The radiation dose was too large to allow the animals to recover or to be imaged repeatedly.

Topics

Medical terms in this study, explained in our Lexicon: Deposition.

Related studies

• Real-time non-invasive detection of inhalable particulates delivered into live mouse airways — M. Donnelley, K.S. Morgan, et al. (2009)
• Airway wall remodeling induced by occupational mineral dusts and air pollutant particles — A. Churg, J.L. Wright (2002)
• Selective exposure and analysis of the sheep tracheal lobe as a model for toxicological studies of respirable particles — R. Bégin, S. Massé, et al. (1985)
• Free radical activity associated with the surface of particles: a unifying factor in determining biological activity? — K. Donaldson, P.H. Beswick, et al. (1996)
• Clearing and mounting techniques for the evaluation of asbestos fibres by the membrane filter method — J.M. Le Guen, S. Galvin (1981)
• Stimulation of oxidant production in alveolar macrophages by pollutant and latex particles — G.E. Hatch, D.E. Gardner, et al. (1980)

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