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.

Role of alveolar phospholipids in bleomycin-induced pulmonary fibrosis in the rat.

The events leading to the onset of the experimental bleomycin-induced pulmonary fibrosis are so far unknown, though recent observations emphasize the crucial role played by lung phospholipids and by alveolar macrophages. In an attempt to verify this point, a series of studies were undertaken by treating rats (CD-COBS) with intratracheal instillation of a single dose of bleomycin (1.5 U). At the same time a group of animals was pretreated with ambroxol (which is known to be a powerful inducer of surfactant production both in fetal and adult type II pneumocytes), 4 mg/kg body weight/day per os, 5 days before the treatment with bleomycin and up to the sacrifice of the animals at the 1st, 3rd, 7th, 14th or 28th day from the instillation. In our experimental model, the 14th day from the treatment with bleomycin seems to be a crucial time since it histologically corresponds to the proliferation of type II pneumocytes; furthermore, an increase of total lecithins in the alveolar spaces was observed, together with an increase of macrophage membrane fluidity. In the ambroxol-pretreated group a partial reduction of the rate of interstitial fibrosis was observed. At the 14th day from treatment the alteration of phospholipid levels was much less pronounced and the microviscosity of alveolar macrophages was similar to that of control animals. These data suggest that the onset of bleomycin-induced pulmonary fibrosis in the rat is characterized by an increase of alveolar lecithins and that this fact could modify the physico-chemical peculiarities of alveolar macrophages. Ambroxol shows a partially protective effect, perhaps by modulating the activity of type II pneumocytes.

In vivo studies of rat alveolar macrophage [corrected] microviscosity: influence of pulmonary surfactant synthesis stimulation.

The influence of pharmacological stimulation of pulmonary surfactant synthesis has been studied in rat alveolar spaces. Animals were treated acutely with Ambroxol at a dose of 4 mg/kg b.w./day p.o. and 5 days later the following biochemical and physico-chemical parameters were determined: BAL fluid lecithin content, BAL fluid microviscosity, alveolar macrophage membrane microviscosity, spontaneous generation of superoxide anion by alveolar macrophages, elastase and antielastase activity of BAL fluid. Treatment with Ambroxol significantly increased the lecithin content of BAL fluid and significantly decreased the macrophage plasma membrane microviscosity. A likely consequence of increased lecithin content in alveolar macrophages (an activation of these cells) was suggested by the increase of the spontaneous production of superoxide. Finally, in the BAL fluid of Ambroxol-treated rats the elastase activity was reduced, whereas the elastase inhibitory activity was almost doubled in respect to control rats.

The behaviour of lung surfactant in electrolyte solutions.

Surface and electrokinetic properties of purified calf lung surfactant in various electrolyte solutions were determined. Surface properties were pH dependent in distilled water and the surfactant performed as a good lung surfactant only below pH 4. In more physiological media it was pH insensitive over the range 2-8.5. In distilled water at pH 6 its surface properties improved when NaCl was added up to 20 mM; above this concentration it had the surface properties required to stabilise alveoli. The surface properties of surfactant in distilled water were also restored by certain cations (Ca2+, Mg2+, Mn2+, Cd2+ and Ni2+) but not others (Na+, K+, La3+ and Fe3+) when added to an ionic strength of 5.6 mM. Cations that restored its surface activity also reduced the surface charge density on the surfactant particles. Aggregation of surfactant by various metal chlorides was studied by light scattering measurements and bore no relation to surface activity or the charge on the particles. Aggregation of surfactant particles by Ca2+, Cd2+ and Mn2+ was instantly reversed by addition of excess EGTA. The influence of electrolytes on the surface properties of lung surfactant is explained in terms of the electrostatic forces operating in the system.

Ambroxol and pulmonary toxicity induced by antineoplastic drugs.

The authors describe the potential effects of ambroxol on the pulmonary disorders induced by antineoplastic agents (in particular, bleomycin and the nitrosureas). An experimental stage focussed attention on the early modifications occurring in the alveolar surfactant and in the afflux of inflammatory and immune-effector cells following bleomycin-induced lung fibrosis in the rat (by intratracheal instillation). The ambroxol-protected rats showed a slower drop of alveolar lecithins in the first few hours after bleomycin administration and a lower afflux of neutrophils, macrophages and lymphocytes. In the clinical stage, respiratory function was studied in two groups of cancer patients treated with nitrosureas or bleomycin. Preliminary findings indicate a rapid worsening of some functional parameters--maximal expiratory flow at 25% vital capacity, diffusing capacity for carbon monoxide and diffusing capacity/ventilation--in controls, while no such changes occurred in the ambroxol-protected subjects. The possible pathogenetic implications of these results and perspective for future investigations are discussed.