ALTERATION OF PULMONARY SURFACTANT PROTEINS IN RATS CHRONICALLY EXPOSED TO CIGARETTE-SMOKE

Surfactant proteins (SP) play an important role in enhancing the surfa ce properties of pulmonary surfactant and participate in host-defense mechanism(s) of the lung, Although it is known that cigarette smoking alters both pulmonary surfactant lipid composition and function, its e ffect on SPs is unknown. The present study was carried out to determin e if chronic exposure to cigarette smoke alters pulmonary SPs, namely, SP-A and SP-B, in a rat model. Sprague-Dawley rats were exposed to ci garette smoke in a nose-only exposure system twice a day, every day fo r 70 weeks. At termination, bronchoalveolar lavage (BAL) fluid and the lung tissues were collected from room control, sham-treated (SH), and smoke-exposed (SM) animals for analyses. The total protein levels in the BAL fluid of SM rats tended to be higher but were not statisticall y different from those of the SH group. However, the albumin content o f BAL fluid in SM rats, measured by quantitative immunoblotting, was s ignificantly higher than in control groups. Compared to control groups , SP-A and SP-B levels in the BAL fluid of SM rats were significantly reduced by 25 and 50%, respectively, when expressed as units per micro gram of BAL fluid protein. However, when calculated as total BAL fluid SP recovered per rat, only the SP-B levels of SM rats were significan tly different from the control groups. Further analysis by ELISA confi rmed the reduced levels of SP-B in SM rats. In contrast to BAL fluid, the lung tissue levels of SP and their respective mRNAs were not signi ficantly different between the control and smoke-exposed groups. These results show a selective reduction in SP-B content on the bronchoalve olar surface following chronic exposure to cigarette smoke and suggest an inhibitory effect of cigarette smoke on surfactant secretory proce sses and/or a localized destruction of SPs on the bronchoalveolar surf ace. (C) 1996 Academic Press, Inc.