MECHANISMS OF SURFACTANT INHIBITION

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Key surfactant protein functions, such as lipid mixing, adsorption, and dynamic compression, that are associated with amphipathic domains are probably the most affected by surfactant inhibitors. Based on the known amino acid sequences of the surfactant proteins SP-A, SP-B, and SP-C, we will synthesize a family of peptides for use in characterizing the interactions of synthetic surfactant dispersions with surfactant inhibitors. These peptides will include short length, functional domains (eg. amphipathic and transmembrane sequences) of SP-A, SP-B, SP-C and full-length proteins representing SP-B (78 residues) and SP-C (35 residues). To evaluate the inhibitory actions of serum components such as serum albumin and anti-surfactant protein antibodies, synthetic peptides will be tested for their in vitro surface activity with and without inhibitors. Surfactant inhibitors will also be investigated for their effects on the mixing function of the surfactant dispersions using fluorescence vesicle assays. These studies will allow a better understanding of which surfactant protein functions (i.e., adsorption, spreading, dynamic compression and respreading, lipid mixing) are perturbed by inhibitors. With the information derived from these in vitro tests of surfactant inhibition, we will assess the interactions between surfactant peptides and inhibitors using physical-biochemical techniques, such as circular dichroism (CD), Fourier transform infrared (FTIR) and electron spin resonance (ESR) spectroscopy, to evaluate whether protein inhibitors (e.g., albumin, anti-surfactant protein antibodies) block surfactant activity by interacting with the amphipathic, surface-seeking domains of surfactant proteins. Finally, the effectiveness of synthetic peptide-lipid mixtures, with and without inhibitor proteins, in restoring lung function will be tested in two animal models of surfactant deficiency and inactivation. These experiments should provide information on dose-response relationships of synthetic surfactant preparations in vivo and identify those conditions under which the in vitro findings of the inhibitor studies predict the in vivo function of synthetic surfactants. This information may not only help in determining component(s) of a surfactant dispersion resist inhibitors, but also in designing synthetic surfactants that offer resistance against inhibition in the respiratory distress syndrome.