Polyunsaturated Phospholipid Modified Membrane Degradation Catalyzed by a Secreted Phospholipase A2

Abstract

To optimize the compositions of the lipid-based nanomedicine and to advance understanding of the roles of polyunsaturated phospholipids in biological membranes, this study examined the effects of polyunsaturated phospholipids on the degradation of giant unilamellar vesicles catalyzed by a secreted phospholipase A2 (sPLA 2 ) using fluorescence microscopy. Molecular interfacial packing, interaction, and degradation of the films containing various mixing ratios of saturated and polyunsaturated phospholipids were quantified using a Langmuir trough integrated with synchrotron X-ray surface scattering techniques. It was found that a high molar fraction (0.63 and above) of polyunsaturated phospholipids not only enhanced the rate of sPLA 2 -catalyzed vesicle degradation but also changed the vesicle deformation process and degradation product morphology. Hydrolysis of the saturated phospholipids generated highly ordered liquid crystal domains, which was reduced or prohibited by the presence of the polyunsaturated phospholipids in the reactant film.

Impeded Molecular Reorganization by Polyethylene Glycol Conjugation Revealed by X-ray Reflectivity and Diffraction Measurements

“…All the films were exposed to sPLA 2 for 2 h before the XR and GIXD measurements on the degraded films. Our previous studies showed that after DPPC degradation, the interface was covered by monolayer liquid-phase domains of lysoPC accompanied by highly ordered inverted bilayer and trilayer domains of PA-Ca 2+ complexes with oblique packing structures. − The degraded films of DPPC with different amounts of DPPE-PEG5k also contained monolayer domains mixed with inverted bilayer domains of PA-Ca 2+ complexes; however, trilayer domains were not detectable, and a remarkable amount of PA molecules maintained hexagonal packing in the monolayer domains (Figure ).…”

“…Sustained release of encapsulated drugs from PEGylated lipid vesicles, compared to the vesicles without PEG conjugation, has been reported. , Enzyme-catalyzed degradation of the lipids results in the formation of the heterogeneous structures of loosely packed lysoPC and highly organized multilayer domains of PA–Ca 2+ complexes, which induces the holes on the vesicles and thus causes leakage of the encapsulated drug. ,, The impeding effects of PEG conjugation on lysoPC and PA microphase separation and thus the formation of the heterogeneous structures provide a possible mechanistic explanation of the sustained drug release from PEGylated lipid vesicles.…”

“…The positions and intensity ratios of the five Bragg peaks obtained from the degraded DPPC film were similar to those of peaks obtained from a PA film on the same Ca buffer. 32,33 When including 5% or 10% DPPE-PEG5k in the films, an additional in-plane peak emerged at 1.5 Å −1 (Figure 4B and C). Further increasing the molar fraction of DPPE-PEG5k to 15% resulted in more pronounced intensity of this single in-plane peak (Figure 4B and C).…”

“…XR and GIXD experiments were conducted using a Langmuir trough integrated with the synchrotron X-ray beamline at the National Science Foundation’s (NSF’s) ChemMatCARS (sector 15C of Advanced Photon Sources) at Argonne National Laboratory. Details of the experimental setup were described in our previous studies. − The X-ray wavelength was 1.24 Å, and all experiments were conducted at about 22.7 °C.…”

Knowledge-Based Design of 5-Fluororacil Prodrug Liposomal Formulation: Molecular Packing and Interaction Revealed by Interfacial Isotherms and X-ray Scattering Techniques

“…The X-ray wavelength was 1.24 Å. Details of the experimental setup were described in our previous publications. − Briefly, a custom-made Langmuir trough (78 mm × 177.6 mm) with a single barrier was filled with 60 mL of PBS buffer. The trough is placed inside a gastight box.…”