Validating the use of napsin A as a marker for identifying tumorigenic potential of lung bronchiolo-alveolar hyperplasia in rodents

There are two types of bronchiolo-alveolar hyperplasia (hyperplasia) in rodent lungs. The first is “inflammatory hyperplasia” that retains its ability to revert to normal epithelia upon removal of the stimulating insult. The second is “latent tumorigenic hyperplasia”, which is irreversible and causes independent preneoplastic lesions that can progress to bronchiolo-alveolar adenocarcinoma. Previously, lung samples with hyperplastic lesions were obtained from rats exposed to N-bis (2-hydroxypropyl) nitrosamine (DHPN) and fine particles (e.g. quartz), and 19 specific markers were examined immunohistochemically to identify latent tumorigenic hyperplasia. In the cytoplasm of the cells that make up the alveolar wall, we found that napsin A was weakly expressed in the inflammatory hyperplastic lesions, and was strongly expressed in the latent tumorigenic hyperplastic lesions induced by DHPN.To validate the possibility that napsin A may serve as a tumorigenic hyperplastic marker, additional experiments were performed with rats and mice. Latent tumorigenic hyperplasia induced by various carcinogens were positive for napsin A, similar to hyperplasia induced by DHPN. Thus, high expression of napsin A in alveolar walls may serve as a useful marker for detecting the tumorigenic potential of lung hyperplasia in rodents.