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Short-term inhalation and in vitro tests as predictors of fiber pathogenicity
R T Cullen1, B G Miller, J M Davis
1Institute of Occupational Medicine, Edinburgh, United Kingdom. rt_cullen@iomhq.org.uk
Abstract:
A wide range of fiber types was tested in two in vitro assays: toxicity to A549 epithelial cells, as detachment from substrate, and the production of the proinflammatory cytokine tumor necrosis factor (TNF) by rat alveolar macrophages. Three of the fibers were also studied in vivo, using short-term inhalation followed by a) bronchoalveolar lavage to assess the inflammatory response and b) measurement of cell proliferation in terminal bronchioles and alveolar ducts, using incorporation of bromodeoxyuridine (BrdU). The amount of TNF produced by macrophages in vitro depended on the fiber type, with the man-made vitreous fibers, and refractory ceramic fibers being least stimulatory and silicon carbide (SiC) whiskers providing the greatest stimulation. In the epithelial detachment assay there were dose-dependent differences in the toxicity of the various fibers, with long amosite being the most toxic. However, there was no clear relationship to known chronic pathogenicity. Fibers studied by short-term inhalation produced some inflammation, but there was no clear discrimination between the responses to code 100/475 glass fibers and the more pathogenic amosite and SiC. However, measurements of BrdU uptake into lung cells showed that amosite and SiC produced a greater reaction than code 100/475, which itself caused no more proliferation than that seen in untreated lungs. These results mirror the pathogenicity ranking of the fibers in long-term experiments. In conclusion, the only test to show potential as a predictive measure of pathogenicity was that of cell proliferation in lungs after brief inhalation exposure (BrdU assay). We believe that this assay should be validated with a wider range of fibers, doses, and time points.
Insights
The bromodeoxyuridine (BrdU) assay, measuring cell proliferation after short-term fiber inhalation, shows promise for predicting long-term lung pathogenicity. Other in vitro and in vivo tests were less effective in discriminating fiber toxicity.
Area of Science:
- Toxicology
- Inhalation Exposure
- Biomarkers
Background:
- Assessing the pathogenicity of different fiber types is crucial for occupational health.
- Existing in vitro and in vivo assays have limitations in predicting chronic lung disease outcomes.
Purpose of the Study:
- To evaluate the predictive potential of various in vitro and short-term in vivo assays for determining fiber pathogenicity.
- To compare the inflammatory and proliferative responses induced by different fiber types.
Main Methods:
- In vitro assays: A549 epithelial cell toxicity (detachment) and rat alveolar macrophage tumor necrosis factor (TNF) production.
- In vivo assays: Short-term inhalation of fibers, bronchoalveolar lavage for inflammation, and bromodeoxyuridine (BrdU) incorporation for cell proliferation.
Main Results:
- In vitro TNF production varied by fiber type; silicon carbide (SiC) whiskers were most stimulatory.
- Amosite fibers showed highest toxicity in the epithelial detachment assay, but no clear correlation with chronic pathogenicity.
- In vivo BrdU assay indicated higher cell proliferation with amosite and SiC fibers compared to glass fibers, mirroring long-term pathogenicity.
Conclusions:
- The bromodeoxyuridine (BrdU) cell proliferation assay following short-term inhalation shows the most potential for predicting fiber lung pathogenicity.
- Further validation of the BrdU assay with diverse fibers, doses, and time points is recommended.