Speaker
Description
The emergence of highly resistant bacterial strains poses a major threat to patients, driven by extensive global use of antibiotics. In pulmonary infections, antibiotics are widely used, making bacterial resistance a serious risk. Cathelicidins (CATH) are antimicrobial peptides of the innate immune system in various organisms, including humans. CATHs act by interacting with negatively charged bacterial membranes, enabled by their positive net charge. We studied the effect of human cathelicidin, LL-37, and three chicken CATHs on the lipid bilayer. The CATHs selected for the study differ in charge at physiological pH (+6 to +9) and in hydrophobic amino acid content in ascending order, LL-37 < CATH-2 < CATH-1 < CATH-3. The therapeutic use of CATHs in respiratory infections has been explored, but their clinical application is limited by difficulties in delivering sufficient amounts to lung tissues. Therefore, exogenous pulmonary surfactant has been proposed as a drug carrier. Pulmonary surfactant (PS) is a lipid-protein mixture that reduces surface tension at the alveolar air–liquid interface, decreasing the work of breathing. PS is essential for gas exchange, and its deficiency or dysfunction can cause respiratory distress syndrome (RDS), which is treated with exogenous PS, such as porcine Curosurf®.
We used neutron membrane diffraction to examine how CATHs affect the structure of the lung surfactant lipid bilayer. A PS model system composed of diC16:0PC/16:0–18:1PC/16:0–18:2PC/16:0–18:1PG in a 50:24:16:10 wt% ratio closely reproduces the functional properties of Curosurf®. The oriented lipid bilayers of CATH/PS were deposited on silica wafers and hydrated from vapor at several relative humidities (80% - 99%). To modulate the contrast between the lipid and aqueous phases, four D2O/H2O mixtures (100%, 70%, 40%, and 8%) were used. The contrast variation technique enables the solution of the phase problem necessary for the Fourier reconstruction of one-dimensional neutron scattering length density (NSLD) profiles. This model-free approach to the structure of the lipid bilayer allows to determine the thickness of the lipid bilayer, the distribution of water across the membrane, and the width of the bilayer–water interface. The data obtained help us to assess the perturbing effect of CATHs on the membrane of PS.
Acknowledgements
Membrane diffraction experiments were performed at the D16 spectrometer at ILL, Grenoble. DOI: 10.5291/ILL-DATA.8-02-1080. Experiments were supported by the VEGA 1/0305/24 project.
