Review of animal/in vitro data on biological effects of man-made fibers

Our plain-English summary of Review of animal/in vitro data on biological effects of man-made fibers, by S.A. Ellouk, M.C. Jaurand (Environmental Health Perspectives, 1994).

The study

• Authors: S.A. Ellouk, M.C. Jaurand
• Journal: Environmental Health Perspectives
• Published: 1994;102 Suppl 2(Suppl 2):47-61
• Type of article: Review
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

This paper reviews the investigations with man-made fibers (MMF). Insulation woods: glasswool (GW), rockwool (RW), slagwool (SW), glass microfibers (GMF), glass filaments (GFiI), and refractory ceramic fibers (RCF) have been used in experimental animals and in in vitro cell systems. A large heterogeneous number of fibers, methods of fiber preparation, size selection, aerosolization, fiber size, and fiber burden measurement were noted, rendering difficult a comparison between results. By inhalation, RCF and asbestos used as positive controls produced a significant tumor increase. In some studies, a low tumor yield was found after inhalation of insulation wools; when all inhalation data were gathered, a significant tumor increase was found with GW. However, it is difficult to draw definitive conclusions on the potential of other fiber types because, in addition to the different compositions of the fibers, differences in fiber number and sizes existed, especially in comparison with asbestos. Moreover, experiments using inoculation, especially by the intraperitoneal route revealed a carcinogenic potential of all fibers types but GFiI and SW. In these two groups a small number of animals has been investigated and the fiber characteristics were sometimes irrelevant. So far, a relationship between the carcinogenic potency and fiber dimensions has been established. Other fiber parameters may be of importance (surface chemistry, biopersistence, fiber structure, for example) but further investigations are necessary to determine the correlations between these parameters and tumor incidence. In vitro experiments have emphasized the fiber characteristics identified in vivo as playing a role in the carcinogenic potency and should be developed as a better approach of the mechanistic effects of MMF.

In plain English

This article reviewed published animal and laboratory cell studies of man-made fibers: glasswool, rockwool, slagwool, glass microfibers, glass filaments and refractory ceramic fibers. These were often compared with asbestos. Pooling rat inhalation studies of glasswool and other insulation glass fibers, the authors found that 29 of 1290 exposed rats developed tumors, a significant difference from control animals (p less than 0.03). Refractory ceramic fibers significantly increased tumors by inhalation in rats and in hamsters, although tumor percentages differed between studies. Glass microfibers produced no significant tumor increase by inhalation across 515 rats. Injection into the abdominal cavity (intraperitoneal inoculation) significantly increased tumors with glasswool, rockwool, glass microfibers and ceramic fibers, but not with slagwool or glass filaments. For example, 159 of 366 rats treated with three types of glass fibers (43.4%) developed tumors. In pooled rat inhalation studies, an overall 14.9% of asbestos-exposed rats had tumors, against 1.9% (15/777) of unexposed or sham-exposed rats. The authors concluded that fiber length and thickness seemed to play a role, with greater carcinogenic potential for long, thin fibers. They cautioned that differences in fiber number and size, especially compared with asbestos, made comparisons difficult.

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: Review of published animal (in vivo) and cell culture (in vitro) studies, with the authors pooling results by fiber type and route of exposure
• Who was studied: Published experiments mainly in rats, also hamsters, guinea pigs, mice and monkeys, plus in vitro cell systems
• Exposure: Man-made fibers (glasswool, rockwool, slagwool, glass microfibers, glass filaments, refractory ceramic fibers), given by inhalation, intratracheal instillation, or intrapleural or intraperitoneal inoculation. Asbestos (chrysotile, crocidolite, amosite) was often used as a positive control.
• Main results:
  • The glasswool section also covered other insulation glass fibers when the reviewed paper gave no further information on the glasswool
  • Inhalation of glasswool or other insulation glass fibers, rats, all studies combined: 29 of 1290 exposed rats developed tumors
  • This combined difference from air or unmanipulated controls was significant (p less than 0.03)
  • Intraperitoneal inoculation in rats with three types of glass fibers: 159 of 366 rats (43.4%) had tumors
  • Asbestos-treated rats (chrysotile or crocidolite) in the intraperitoneal glass fiber experiments: 45.7% formed tumors
  • Slagwool did not produce a significant tumor increase
  • Rockwool inhalation in rats: 2 tumors in 95 rats (2.1%), not significant compared with controls
  • Rockwool intraperitoneal inoculation in rats: 35.8% had tumors (p less than 0.001, treated versus untreated)
  • Glass microfiber inhalation: no significant tumor increase in a total of 515 rats across six studies
  • Refractory ceramic fiber inhalation: overall significant tumor production in rats (p less than 0.001) and hamsters (p less than 0.001)
  • Refractory ceramic fiber inhalation: tumor percentages differed between studies
  • In hamsters, the significant overall response to refractory ceramic fibers came from one study (Hesterberg et al.), which reported a mesothelioma rate reaching 42%
  • Intraperitoneal inoculation significantly increased tumors with glasswool, rockwool, glass microfibers and refractory ceramic fibers, but not with slagwool or glass filaments
  • Pooled rat inhalation studies: overall 14.9% tumors in asbestos-exposed rats
  • Pooled rat inhalation studies: 1.9% (15/777) tumors in unexposed or sham-exposed rats
• The authors' conclusion: The authors concluded that fiber length and thickness seem to play a role in tumor formation by all routes, with greater carcinogenic potential for long and thin fibers. They also concluded that no clear-cut conclusion could be drawn on fiber durability.
• Limitations the authors state:
  • The studies used heterogeneous fibers and methods of preparation, aerosolization and measurement, which made comparisons difficult
  • Fiber composition, number and size differed, especially compared with asbestos
  • Combining data from different studies calls for caution, because each study's weight depends on its number of animals
  • Few animals were studied for glass filaments and slagwool, and fiber characteristics were sometimes irrelevant
  • Some inhalation studies used fibers too thick to be deposited in rodent airways

Topics

Medical terms in this study, explained in our Lexicon: Fiber Burden, Carcinogenic, Fiber Dimensions, biopersistence.

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• Relationship between lung biopersistence and biological effects of man-made vitreous fibers after chronic inhalation in rats — T.W. Hesterberg, W.C. Miiller, et al. (1994)
• Short-term inhalation and in vitro tests as predictors of fiber pathogenicity — R.T. Cullen, B.G. Miller, et al. (1997)
• In vitro cytotoxicity of asbestos and man-made vitreous fibers: roles of fiber length, diameter and composition — G.A. Hart, L.M. Kathman, et al. (1994)
• Biological effects of naturally occurring and man-made fibres: in vitro cytotoxicity and mutagenesis in mammalian cells — R. Okayasu, L. Wu, et al. (1999)
• Man-made mineral fibers and interstitial lung diseases — E. Fireman (2014)

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