Characteristics of surfactant proteins in tumorigenic and inflammatory lung lesions in rodents

Surfactant proteins (SPs) are essential for the proper structure and respiratory function of the lungs. There are four subtypes of SPs: SP-A, SP-B, SP-C, and SP-D. The expectorant drug ambroxol hydrochloride is clinically used to stimulate pulmonary surfactant and airway serous secretion. In addition, previous studies showed that ambroxol regulated SP production and attenuated pulmonary inflammation, with ambroxol hydrochloride being found to suppress quartz-induced lung inflammation via stimulation of pulmonary surfactant and airway serous secretion. In this study, we investigated the expression of SP-A, SP-B, SP-C, and SP-D in neoplastic and inflammatory lung lesions in rodents, as well as their possible application as potential markers for diagnostic purposes. SP-B and SP-C showed strong expression in lung hyperplasia and adenoma, whereas SP-A and SP-D were expressed in the mucus or exudates of inflammatory alveoli. Rodent tumorigenic hyperplasic tissues induced by various carcinogens were positive for napsin A, an aspartic proteinase involved in the maturation of SP-B; this indicated a focal increase in type II pneumocytes in the lungs. Therefore, high expression of napsin A in the alveolar walls may serve as a useful marker for prediction of the tumorigenic potential of lung hyperplasia in rodents.