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Key Event Title
Increase, Respiratory or Squamous Metaplasia
Key Event Components
Key Event Overview
AOPs Including This Key Event
Key Event Description
Sustained atrophy/degeneration olfactory epithelium under the influence of a cytotoxic agent leads to adaptive tissue remodeling. Cell types unique to olfactory epithelium, e.g. olfactory neurons, sustentacular cells and Bowmans glands, are replaced by cell types comprising respiratory epithelium or squamous epithelium.
How It Is Measured or Detected
Respiratory or squamous metaplasia is measured histologically is cross-sections of the nose after H&E staining and/or use of immunohistochemical markers to show the absence of olfactory epithelial cell types and the presence of cell types of the respiratory or squamous epithelium. Olfactory epithelium is normally composed of X cell types. Respiratory epithelium is composed of Y cell types: The squamous epithelium is composed of Z cell types. The absence of structures such as Bowmans glands and olfactory bundles are also markers of the initial step of respiratory metaplasia. Immunohistochemical staining for olfactory marker protein is used to determine the absence of olfactory sensory neurons. Staining for AB/PAS-positive mucosubstances is used to determine the presence mucous cells, which are normally present in respiratory epithelium. The key features of transitional epiethelium metaplasia are the presence of tall columnar cells with cilia on the luminal surface, basal cells, and nonciliated cuboidal to columnar cells.
Domain of Applicability
This event has been observed in the olfactory epithelium of rats and mice exposed by inhalation to one or more of the listed chemical initiators. Degeneration, necrosis and atrophy are expected in humans based conserved properties of the olfactory epithelium across species.
- ↑ Islam, Amuzie, Harkema and Pestka (2007). Neurotoxicity and inflammation in the nasal airways of mice exposed to the macrocyclic trichothecene mycotoxin roridin a: kinetics and potentiation by bacterial lipopolysaccharide coexposure. Toxicol Sci. 98: 526-541
- ↑ Wagner, Van Dyken, Hotchkiss and Harkema (2001). Endotoxin enhancement of ozone-induced mucous cell metaplasia is neutrophil-dependent in rat nasal epithelium. Toxicol Sci. 60: 338-347
- ↑ Hardisty, Garman, Harkema, Lomax and Morgan (1999). Histopathology of nasal olfactory mucosa from selected inhalation toxicity studies conducted with volatile chemicals. Toxicol Pathol. 27: 618-627