The effect of lung burden on biopersistence and pulmonary effects in rats exposed to potassium octatitanate whiskers by inhalation

Our plain-English summary of The effect of lung burden on biopersistence and pulmonary effects in rats exposed to potassium octatitanate whiskers by inhalation, by T. Oyabu, H. Yamato, A. Ogami, et al (Journal of Occupational Health, 2004).

The study

• Authors: T. Oyabu, H. Yamato, A. Ogami, Y. Morimoto, I. Akiyama, S. Ishimatsu, H. Hori, I. Tanaka
• Journal: Journal of Occupational Health
• Published: 2004;46(5):382-90
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The effect of lung burden on biopersistence and histopathological changes caused by potassium octatitanate whiskers (POW) which is one of the asbestos substitutes were investigated for 1-yr and 4-wk inhalation periods. In the 1-yr inhalation experiment, male Wistar rats were exposed to POW (TW) for 6 h/d, 5 d/wk under the same conditions as a previous study of POW (PT1, JFM fiber) which is made by different manufacturer. The exposure concentration was 1.9 +/- 0.7 mg/m(3) and the mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) in the chamber were 1.6 microm and 2.9. Rats were sacrificed at 3 d and 1 yr after the inhalation experiment and TW deposits in the lungs were determined by ICP-AES. Lung burden at 3 d and 1 yr after the inhalation was 2.39 +/- 0.50 mg and 1.37 +/- 0.96 mg, respectively, the deposition fraction was 8.1% and biological half time (BHT) was 15 months. Aggregated dust cells and mild fibrotic changes around these dust cells were observed in the exposed rat lung. These results were almost the same as those obtained in the previous 1-yr PT1 study. In the 4-wk inhalation experiment, to investigate the effect of lung burden on biopersistence and histopathological change, male Wistar rats were exposed to PT1. The exposure concentration was 102 +/- 21 mg/m(3), MMAD (GSD), the geometiric mean length and diameter (GSD) of the PT1 in the chamber were 1.6 microm (3.0), 2.2 microm (1.8) and 0.33 microm (1.5), respectively. Rats were sacrificed at 3 d, 1 wk, and 1, 3, 6 and 12 months after the inhalation experiment. The lung burden of POW at 3 d after 4 wk inhalation was 1.49 +/- 0.19 mg, which was close to the estimated amount of overload. The BHT of the total mass (4.1 months) was not prolonged, but aggregated dust cells were observed in the subpleural region and around the bronchioles and mild fibrotic changes were observed only around the dust cells at one year after the 4-wk inhalation. It is considered that the excessive exposure which impairs the function of alveolar macrophage mediated clearance may cause the aggregation of dust cells and fibrotic changes.

In plain English

This animal study tested potassium octatitanate whiskers (POW), an asbestos substitute, in male Wistar rats. In the first experiment, 27 rats breathed one manufacturer's POW (TW), averaging 1.9 mg/m3, 6 hours a day, 5 days a week, for one year; 25 controls breathed clean air. Lungs held 2.39 mg of TW three days after exposure and 1.37 mg a year later, an approximate half-time of 15 months. These figures nearly matched an earlier one-year study of another manufacturer's POW (PT1). All exposed rats had clumps of dust-laden cells and thickened alveolar walls. Survival was slightly lower in exposed rats, but not statistically significantly. In a second experiment, 30 rats breathed PT1 at 102 mg/m3 for 4 weeks. Three days after exposure their lungs held 1.49 mg; total whisker mass cleared with a 4.1-month half-time, so overall clearance was not slowed. By 12 months, whiskers scattered just after exposure had formed clumped dust cells around the bronchioles and beneath the pleura, with mild fibrotic changes only around them. The authors concluded that excessive exposure impairing macrophage clearance may cause such changes.

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 inhalation experiments in rats: a 1-year inhalation study of TW compared with a previous 1-year study of PT1, plus a 4-week high-concentration inhalation study of PT1
• Who was studied: 1-year experiment: 27 exposed and 25 control Kud:Wistar male rats, aged 5 weeks at the start; 4-week experiment: 30 exposed male Kud:Wistar rats aged 8 weeks, with 5 killed at each of six time points from 3 days to 12 months, and the same number of controls
• Exposure: potassium octatitanate whiskers (an asbestos substitute) from two manufacturers. TW at 1.9 plus or minus 0.7 mg/m3 for 1 year (6 h/day, 5 days/week). PT1 at 102 plus or minus 21 mg/m3 for 4 weeks.
• Main results:
  • 1-year TW group: survival was slightly lower than in controls, but the difference was not statistically significant (p=0.106)
  • 1-year TW group: lung burden was 2.39 plus or minus 0.50 mg at 3 days and 1.37 plus or minus 0.96 mg at 1 year after exposure; deposition fraction 8.1%; biological half time 15 months
  • Retained amounts were almost the same for TW and for the earlier 1-year PT1 study (PT1: 2.36 mg at 3 days, 1.36 mg at 1 year, half time 16 months)
  • 1-year TW group: foci of aggregated dust cells and TW were found, and alveolar wall thickness around TW was seen in all exposed rats
  • 1-year experiment: one epidermoid cyst in the exposed group and one squamous cell carcinoma in the control group
  • 4-week PT1 group: lung burden 3 days after exposure was 1.49 plus or minus 0.19 mg, close to the estimated overload amount
  • 4-week PT1 group: the biological half time of the total mass was 4.1 months, so total-mass clearance was not prolonged. Local aggregates of POW were still observed after 12 months.
  • 4-week PT1 group: POW that was scattered in the lungs just after exposure had formed aggregated dust cells in the subpleural region and around the bronchioles at one year after exposure
  • 4-week PT1 group, 12 months after exposure: mild fibrotic changes were seen only around the aggregated dust cells
  • The authors speculated that a critical lung burden lies between 1.5 mg and 2.4 mg
• The authors' conclusion: The authors concluded that excessive POW exposure that impairs alveolar macrophage-mediated clearance may cause the aggregation of dust cells and fibrotic changes. They also concluded that TW and PT1 did not differ significantly after 1-year inhalation.
• Limitations the authors state:
  • Biological half times in the 1-year study were approximate because they were calculated from very few time points

Topics

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

Related studies

• The effect of lung burden on biopersistence and pulmonary effects in rats exposed to potassium octatitanate whiskers by intratracheal instillation — T. Oyabu, H. Yamato, et al. (2006)
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• Histopathological changes in rat lung following intratracheal instillation of silicon carbide whiskers and potassium octatitanate whiskers — A. Ogami, Y. Morimoto, et al. (2007)
• Inhalation toxicity study of disk-shaped potassium octatitanate particles (terracess TF) in rats following 90 days of aerosol exposure — S. Sakai, K. Inada, et al. (2010)
• Pulmonary effects and biopersistence of deposited silicon carbide whisker after 1-year inhalation in rats — I. Akiyama, A. Ogami, et al. (2007)
• Pulmonary and pleural toxicity of potassium octatitanate fibers, rutile titanium dioxide nanoparticles, and MWCNT-7 in male Fischer 344 rats — M. Abdelgied, A.M. El-Gazzar, et al. (2019)

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