Role of surfactant in alveolar defence against inhaled particles

Alveolar surfactant molecules may concentrate on particulated matter (powders or microbes) with the formation of liposomes. In vitro the spraying of powders on a surfactant film causes the appearance of liposomes and consequent alterations in the tension/area diagram. In animals soon after inhalation of powders fine enough to be deposited in alveoli surfactant liposomes containing powder particles are observed in the alveolar spaces and later on along the airways. The powder content of liposomes collected through a T cannula in the trachea may be demonstrated by chemical or electronic microscopical analysis. Prolonged inhalation of powder may induce surfactant depletion and alveolar bronchiolar instability. In mice exposed for 5 months to silica dust a correlation has been found between surfactant depletion and silica retention in the lung with recruitment of phagocytic cells and increased serum and BAL-lysosomal enzyme activity. In animals treated with ambroxol, the clearance of silica is faster and longer lasting, and the pulmonary alterations are delayed and reduced. The first results of clinical trials with ambroxol in miners seem favorable. Microbes may also be incorporated as powder particles in alveolar surfactant liposomes. Using motile strains, bacteria struggling within a liposome may be observed with a telecamera. Preliminary observations suggest a direct antimicrobial action of ambroxol.