Submitted on February 19, 2004
Accepted on July 15, 2004
Distinct effects of SP-B and SP-C on the uptake of surfactant-like liposomes by alveolar cells in vivo and in vitro
D. L.H. Poelma1, L. J. Zimmermann2, W. A. van Cappellen3, J. J. Haitsma1, B. Lachmann1, and J. F. van Iwaarden2*
1 Department of Anesthesiology, Erasmus MC, Rotterdam, The Netherlands
2 Department of Neonatology, Academic Hospital, Maastricht, The Netherlands
3 Department of Reproduction & Development, Erasmus MC, Rotterdam, The Netherlands
* To whom correspondence should be addressed. E-mail: fviw{at}paed.azm.nl.
The effects of SP-B and SP-C on the uptake of surfactant like liposomes by alveolar type II cells and alveolar macrophages were studied both in vivo and in vitro. In vivo,
mechanically ventilated rats were intra tracheally instilled with fluorescent labeled liposomes that had SP-B and/or SP-C incorporated in different concentrations.
Consequently the alveolar cells were isolated and cell-associated fluorescence was determined using flow cytometry. The results show that the incorporation of SP-B
does not influence the uptake, nor in the presence of essential co-factors. The inclusion of SP-C in the liposomes enhanced the by alveolar type II cells at a SP-C to lipid ratio of 2:100. If divalent cations (calcium and magnesium) were present at physiological concentrations in the liposomes suspension, uptake of liposomes by
alveolar macrophages was also enhanced. In vitro, the incorporation of SP-B affected uptake only at a protein to lipid ratio of 8:100, whereas the inclusion of SP-C in the
liposomes leads to an increased uptake at a protein to lipid ratio of 1:100. From these results it can be concluded that SP-B is unlikely to affect uptake of surfactant, whereas SP-C in combination with divalent cations and other solutes are capable of increasing the uptake.
