Biophysical Modulation of Endothelial Membranes: Molecular-Scale Effects of Oxidized Phospholipids

Biologically active oxidized phospholipids (oxPCs) such as 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC) and 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphocholine (PGPC) are known to exert multiple pathophysiological effects. At elevated oxPC concentrations, disruption of the endothelial barrier and induction of monocyte adhesion to endothelial cells results. The specific mechanisms by which oxPCs modulate membrane barrier function are poorly understood. These effects are further implicated in a range of disorders, including certain cardiovascular, metabolic, and immunological diseases.

We investigated the influence of these two bioactive oxidized phospholipids on model bilayer properties, membrane packing, and endothelial cell biomechanics both computationally and experimentally. Using a combination of coarse-grained molecular dynamics simulations, Laurdan multi-photon imaging, and atomic force microscopy (AFM) microindentation experiments, the impacts of the analogous truncated tail phospholipids, POVPC (aldehyde-terminated) and PGPC (carboxyl-terminated), on the structure of a multicomponent phospholipid bilayer was determined, and the consequences of their incorporation on membrane packing and endothelial cell stiffness was assessed.

Our molecular simulations predicted differential bilayer perturbation effects of the two oxidized phospholipids based on the chemical identities of their truncated tails. We showed that for the analogous oxPCs incorporated in a phosphatidylcholine bilayer containing sphingomyelin, the carboxylic analog, PGPC, experienced more significant reorientation of the truncated tail and displacement of the oxidized lipid from the plane of the bilayer. These phenomena induced greater perturbation in the structure of the lipid bilayer than the aldehyde analog, POVPC. Decreased bilayer packing and increased water permeation was observed, which was consistent with Laurdan imaging results. Computational predictions of larger membrane perturbation by PGPC corresponded with greater stiffness observed for PGPC-treated endothelial cells measured by cellular elastic moduli using AFM.