Ozone enhances the uptake of mineral particles by tracheobronchial epithelial cells in organ culture

Our plain-English summary of Ozone enhances the uptake of mineral particles by tracheobronchial epithelial cells in organ culture, by A. Churg, M. Brauer, B. Keeling (American Journal of Respiratory and Critical Care Medicine, 1996).

The study

• Authors: A. Churg, M. Brauer, B. Keeling
• Journal: American Journal of Respiratory and Critical Care Medicine
• Published: 1996;153(4 Pt 1):1230-3
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We have previously shown that the basal uptake of mineral particles by tracheobronchial epithelial cells in organ culture is mediated in part by active oxygen species (AOS) and can be greatly augmented by exposure to cigarette smoke, a concentrated source of AOS, and other radicals. We hypothesized that ozone, another generator of AOS in tissues, might have the same effect. To test this hypothesis, tracheal explants were exposed to room air (control) or ozone in varying concentrations from 0.01 to 1.0 ppm for 10 min, and subsequently to a suspension of either amosite asbestos or titanium dioxide (rutile) for 1 h. Explants were then transferred to an air/CO2 incubator for 1 wk to allow particle uptake to occur, and uptake was determined by morphometry. We found that ozone exposure increased the uptake of both asbestos and titanium dioxide in a dose-response fashion; this effect appeared at lower exposure levels and was more marked with titanium dioxide than with amosite. The ozone effect could be prevented by addition of catalase but not superoxide dismutase to the particle suspension, or by preincubation of the particles with deferoxamine. These observations indicate that ozone can directly increase uptake of mineral particles by tracheobronchial epithelial cells; this effect occurs with brief exposures at very low ozone levels and appears to be mediated by hydrogen peroxide and possibly by hydroxyl radical. These findings support the general hypothesis that AOS are important mediators of epithelial particle uptake in many different settings. Enhanced uptake may be one of the mechanisms by which ozone impairs particle clearance from the lung and may play a role in the increased morbidity seen in populations with exposure to high levels of both ozone and atmospheric particulates.

In plain English

This laboratory study used small pieces of windpipe (tracheal explants) from Sprague-Dawley rats, grown in culture, with five or six explants per treatment group. Explants were exposed for 10 minutes to room air or to ozone at 0.01 to 1.0 ppm, then for 1 hour to a suspension of amosite asbestos or titanium dioxide (rutile) particles. After 7 days, the authors measured particle uptake by the lining (epithelial) cells under a microscope. Ozone increased titanium dioxide uptake at every concentration tested, but increased amosite uptake only at the two highest concentrations. For both, uptake tended to rise with ozone level (correlation coefficients 0.35 for titanium dioxide, 0.38 for amosite). The effect was relatively greater for titanium dioxide. At 0.1 ppm ozone, the increase was prevented by adding the enzyme catalase or by pretreating particles with the iron-binding drug deferoxamine, but not by superoxide dismutase. The authors concluded that ozone can directly increase particle uptake by these cells, apparently through hydrogen peroxide and possibly hydroxyl radical. They noted that exposing tissue directly to ozone differs greatly from breathing it.

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: Laboratory experiment on rat tracheal tissue in organ culture (explants)
• Who was studied: Tracheal explants about 2 mm in size from 250 g Sprague-Dawley rats, with five or six explants per treatment group. The work was done at the University of British Columbia and Vancouver Hospital; no study dates are given.
• Exposure: Room air (control) or ozone at 0.01 to 1.0 ppm for 10 minutes. This was followed by 1 hour in a suspension of 5 mg/ml amosite asbestos or 4.0 mg/ml titanium dioxide (rutile). In some experiments catalase or superoxide dismutase was added to the dust suspension, or the dusts were pretreated with deferoxamine.
• Main results:
  • Titanium dioxide: uptake was statistically greater than control at all ozone doses. Uptake levels at the different ozone doses were not statistically different from each other.
  • Titanium dioxide: regression analysis showed a dose-response effect, with a correlation coefficient between ozone level and uptake of 0.35 (p = 0.01).
  • Amosite asbestos: uptake was increased (each p less than 0.001 compared with control) only at the two highest ozone doses, 0.1 and 1.0 ppm.
  • Amosite asbestos: there was a dose effect, with a correlation coefficient between ozone level and uptake of 0.38 (p = 0.006).
  • The effect of ozone was relatively greater on titanium dioxide uptake than on amosite uptake.
  • At 0.1 ppm ozone, for both amosite and titanium dioxide, deferoxamine treatment of the dust or catalase in the medium protected against enhanced uptake. Superoxide dismutase had no protective effect.
• The authors' conclusion: The authors concluded that ozone can directly increase the uptake of mineral particles by tracheobronchial epithelial cells, with brief exposures at very low ozone levels. They concluded the effect appears to be mediated by hydrogen peroxide and possibly by hydroxyl radical. They suggested the effects could occur in intact animals and humans.
• Limitations the authors state:
  • Exposing tracheal explants directly to ozone differs greatly from the situation in living animals, where ozone concentration falls from the upper to the lower respiratory tract because of tissue reactions.
  • Why and how a peroxidated cell membrane enhances particle uptake is unknown.
  • The reason for the difference in effect between titanium dioxide and amosite is unclear.

Topics

Medical terms in this study, explained in our Lexicon: Amosite, Dose-response relationship, Superoxide, Hydroxyl Radical.

Related studies

• Effects of cigarette smoke on epithelial uptake of non-asbestos mineral particles in tracheal organ culture — B. Keeling, J. Hobson, et al. (1993)
• Iron enhances uptake of mineral particles and increases lipid peroxidation in tracheal epithelial cells — B. Keeling, K.Y. Li, et al. (1994)
• Mechanisms of asbestos-induced squamous metaplasia in tracheobronchial epithelial cells — G. Cameron, C.D. Woodworth, et al. (1989)
• Effect of mineral particles containing iron on primary cultures of rabbit tracheal epithelial cells: possible implication of oxidative stress — C. Guilianelli, A. Baeza-Squiban, et al. (1993)
• Active oxygen species mediate asbestos fiber uptake by tracheal epithelial cells — J. Hobson, J.L. Wright, et al. (1990)
• Effects of cigarette smoke dose and time after smoke exposure on uptake of asbestos fibers by rat tracheal epithelial cells — A. Churg, J. Hobson, et al. (1990)

Browse more research in American Journal of Respiratory and Critical Care Medicine, or return to medical research.