Speaker
Description
When inhaled general anaesthetics are administered, pulmonary surfactant represents the first biological barrier they interact with. We investigated effects of primary aliphatic n-alcohols (CnOH, n = 8 – 18, 0.4 mol/mol), as simple models of inhaled general anaesthetics, incorporated into synthetic pulmonary surfactant models. Two lipid mixtures were used as model systems: S-model, consisting of dipalmitoylphosphatidylcholine : palmitoyloleoylphosphatidylcholine : palmitoyllinoleoylphosphatidylcholine : palmitoyloleoylphosphatidylglycerol (DPPC : POPC : PLPC : POPG = 50 : 24 : 16 : 10 wt%), and a simpler P-model, containing POPC : POPG = 9:1 wt%. Each mixture was enriched with 0 – 20 wt% polymyxin B (PxB), mimicking the properties of the surfactant protein SP-B.
Structural properties of bilayers were characterised by small- and wide-angle X-ray scattering (SAXS/WAXS) at 20 – 50 °C. Diffraction peaks were fitted using Lorentzian functions. Lattice parameter of the lamellar phase (bilayer repeat distance, d), including the thickness of the lipid bilayer and the water layer, was calculated from the position of the first SAXS reflection. The structural organisation of lipid acyl chains was evaluated from WAXS.
For both models, diffractograms showed lamellar phase with equidistant low-resolution reflections superimposed on a wide diffuse reflection from uni- or oligolamellar liposomes. Negatively charged POPG disrupted the regularity of the lamellar arrangement, resulting in higher d-values. C12OH reversed this effect most. Adding PxB (>5 wt%) into the P model + C12OH system markedly stabilized the lamellar structure, whereas in S-model + C12OH, PxB led to phase separation, especially at 20 °C. WAXS diffractograms at 20 °C showed a diffuse signal for P model, but a peak at q ~ 15 nm^-1, corresponding to acyl chains in gel phase, for S model. At 50 °C, this peak became less pronounced and with PxB <5 wt% disappeared. In homologous series of CnOHs at 20 °C systems showed gel-phase chain organization for C14OH – C18OH in the P-model and for C8OH – C18OH in the S-model, at 50 °C only for C16OH – C18OH.
These results suggest that positively charged PxB (>5 wt%) increases the gel to liquid-crystalline phase transition in the complex S-model and stabilizes negatively charged bilayers via electrostatic interactions with PG headgroups, despite leading to laterally separated domains. In the two-lipid P-model, prevalent unsaturated chains grant the liquid-crystalline phase across 20 – 50 °C, facilitating even PxB distribution. Alcohols increase the lipid order chain-length dependently; d increases with CnOH chain length linearly, reaching values of pure mixtures at C16OH – C18OH, i.e. when CnOH matches the lipid chain length. At 50°C, d is systematically lower due to reduced bilayer thickness.
Research was supported by VEGA 1/0305/24 project. SAXS experiments were performed on the BL11-NCD beamline at ALBA Synchrotron with the collaboration of ALBA staff.
