Histopathological changes in rat lung following intratracheal instillation of silicon carbide whiskers and potassium octatitanate whiskers

Our plain-English summary of Histopathological changes in rat lung following intratracheal instillation of silicon carbide whiskers and potassium octatitanate whiskers, by A. Ogami, Y. Morimoto, T. Myojo, et al (Inhalation Toxicology, 2007).

The study

• Authors: A. Ogami, Y. Morimoto, T. Myojo, T. Oyabu, M. Murakami, K. Nishi, C. Kadoya, I. Tanaka
• Journal: Inhalation Toxicology
• Published: 2007;19(9):753-8
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We evaluated the pattern of pulmonary inflammation for the assessment of the biological hazards of two man-made mineral fibers. Rats were exposed by intratracheal instillation to a 2 mg dose of each of two kinds of man-made mineral fibers (PT1, potassium octatitanate whisker; and SiCW, silicon carbide whisker), or three kinds of comparable respirable particles (crystalline silica, crocidolite asbestos, and titanium dioxide, TiO(2)). The lung tissue was evaluated at 3 day, 1 wk, and 1, 3 and 6 mo after exposure. Digital images taken of the lung sections were examined by morphometric point counting method (PCM). PT1 and SiCW showed a similar inflammatory pattern, which contains temporal inflammation such as moderate alveolitis within 1 wk after the exposure, and in later phase aggregation foci of instilled fibers. Differences in repair patterns of these two man-made mineral fibers showed that the toxicity of these two fibers is less toxic than for crocidolite or crystalline silica. Although SiCW showed a higher inflammation score than TiO(2) within 1 mo after instillation, the inflammation scores and fibrotic changes of PT1 and SiCW were not significant as TiO(2) at 3 mo and 6 mo in this study. Careful use should be recommended when these materials are used in the workplace.

In plain English

This animal experiment tested silicon carbide whiskers (SiCW) and potassium octatitanate whiskers (PT1), two man-made mineral fibers. For each material, 25 male Wistar rats received one 2 mg dose directly into the windpipe. Five rats were examined at each of 3 days, 1 week, and 1, 3 and 6 months. Results were compared with saline-treated controls and with the authors' earlier (2004) results for crocidolite asbestos, crystalline silica and titanium dioxide. Both whiskers caused acute lung inflammation with fiber clumps at 3 days. SiCW inflammation peaked at 1 month and then declined. PT1 average scores were 0.50 to 0.73, lower than crocidolite or silica. Collagen deposition rates were 0.14 to 0.17 for SiCW and 0.14 to 0.16 for PT1. This is the share of sampled lung-tissue points staining for collagen. Crocidolite ranged 0.23 to 0.35 and controls 0.15 to 0.18. At 3 and 6 months, the whiskers' inflammation scores and fibrotic changes did not differ significantly from titanium dioxide's. The authors concluded both whiskers were less toxic than crocidolite or silica. They recommended careful workplace use and called for multiple-dose studies.

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 (single intratracheal instillation in rats, with lung tissue examined over 6 months by point counting of microscope images)
• Who was studied: Male Wistar rats, 9 weeks old at instillation, 25 per material. Five per group were killed at each of 3 days, 1 week, 1 month, 3 months and 6 months. A control group received saline only. The study was done at the University of Occupational and Environmental Health, Japan.
• Exposure: A single 2 mg dose in 0.4 ml saline of silicon carbide whisker (SiCW) or potassium octatitanate whisker (PT1). These were compared with UICC crocidolite, crystalline silica (Min-U-Sil-5) and titanium dioxide, using data from the authors' previous study.
• Main results:
  • At 3 days, the SiCW and PT1 groups showed acute alveolar inflammation with aggregated foci of fibers.
  • In the SiCW group, the inflammation score peaked at 1 month after instillation and then gradually fell below a score of 1.
  • In the PT1 group, the average inflammation score was 0.50 to 0.73 over the observation period, lower than crystalline silica or crocidolite.
  • For comparison, crocidolite averaged an inflammation score of 1.4 at 3 days and 1.5 at 6 months. Crystalline silica averaged 2.3 at 6 months.
  • The collagen deposition rate was the number of collagen-stained points divided by the total number of points in the sampled lung parenchyma. It was 0.14 to 0.17 for SiCW, 0.14 to 0.16 for PT1, 0.23 to 0.35 for crocidolite, and 0.15 to 0.18 for the control group.
  • In the SiCW and PT1 groups, collagen deposition had not progressed at 6 months.
  • At 3 and 6 months, inflammation scores and fibrotic changes for PT1 and SiCW were not statistically significant compared with titanium dioxide.
• The authors' conclusion: The authors concluded that the two man-made mineral fibers were less toxic than crocidolite or crystalline silica. They also stated that careful use should be recommended when these materials are used in the workplace.
• Limitations the authors state:
  • Only one dose (2 mg) was tested. The authors said studies with multiple doses are needed to determine a dose response.

Topics

Medical terms in this study, explained in our Lexicon: Inflammation, Mineral Fiber, Crystalline, Crocidolite, Point Counting.

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)
• Expression of Clara cell secretory protein in the lungs of rats exposed to silicon carbide whisker in vivo — Y. Morimoto, L. Ding, et al. (2003)
• Pulmonary effects and biopersistence of deposited silicon carbide whisker after 1-year inhalation in rats — I. Akiyama, A. Ogami, et al. (2007)
• Expression of heme oxygenase-1 in the lungs of rats exposed to potassium octatitanate whiskers — Y. Obata, Y. Morimoto, et al. (2011)
• Pulmonary response, in vivo, to silicon carbide whiskers — G.L. Vaughan, S.A. Trently, et al. (1993)
• The effect of lung burden on biopersistence and pulmonary effects in rats exposed to potassium octatitanate whiskers by inhalation — T. Oyabu, H. Yamato, et al. (2004)

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