Aim An in vitro cultured monolayer system of alveolar epithelial cells was used as a model to
investigate the transport
pathway peptides or proteins, salmon calcitonin (sCT), insulin (INS),
recombinant hirudin (rHAV2), and recombinant human growth hormone (rhGH), in pulmonary epithelium in vivo.
Methods Human lung adenocarcinoma A549 cells formed continuous monolayers with growing polycarbonate
filters of Transwell plate. Transport studies of macromolecules in the monolayer system were carried out 'after 6
days in culture, The transport of peptides or proteins with MW 3 400-22 000 was studied in cultured human
lung adenocarcinoma A549 cell monolayers at different conditions. Results The results showed that the
apparent permeability coefficients (Papp) of these macromolecules across A549 cell monolayers ranged from
2×10~(-6) to 5×10~(-6) cm's~(-1) and exhibited good inverse correlation with molecule weight. No concentration,
direction and temperature dependence were observed in the permeation of sCT, INS and rHAV2. While the Papp
of rhGH in the BA direction (2.25×10~(-6) cm's~(-1)) was significantly less than that in the reverse direction. The
Papp values of rhGH were concentration and temperature independent in the AB direction. Conclusion These
findings suggest that the hydrophilic peptides and proteins, salmon calcitonin, insulin, recombinant hirudin,
and recombinant human growth hormone used in this study, appeared to penetrate the A549 cell monolayers via
a paracellular pathway by passive diffusion mechanism.