Effect of tobacco extract on surfactant synthesis and its reversal by retinoic acid—role of cell–cell interactions in vitro

Tobacco induces oxidative stress in the alveolar epithelium and causes its damage. Retinoic acid (RA) has a cardinal role in alveolar cell growth, differentiation, and maturation. The aim of the study was to investigate the role of cell–cell interactions and whether RA could reverse the effect of tobacco extract on epithelial function as expressed by surfactant synthesis. For this, an in vitro model, which provides multiple cell type interactions, as seen in vivo, was used. We had used the major lung cell types, alveolar epithelial and mesenchymal cells represented by the cell lines A549 (human lung adenocarcinoma cell line), and human fetal lung fibroblast-1 (HFL-1) for developing the monoculture and co-culture systems and studied the effect of tobacco extract and retinoic acid. The effect of tobacco and retinoic acid both singly and in combination on proliferation and surfactant synthesis was analyzed. Retinoic acid induced proliferation and upregulated surfactant synthesis in monocultures and co-cultures. Tobacco extract at 100 μg/ml concentration decreased A549 proliferation and upregulated surfactant protein mRNA expression. In co-cultures treated with tobacco extract (100 μg/ml), retinoic acid (1 μM), regulated cell proliferation, and surfactant protein mRNA expression vis-à-vis the monoculture system. This clearly points to the fact that cell–cell interactions modulate the effect of additives or stimulants and help in assessing the in vivo combinatorial responses in vitro and that the retinoic acid effect is regenerative.