Regular Article Effects of oxidation on the physicochemical properties of polyunsaturated lipid membranes Elisa Parra-Ortiz a,⇑ , Kathryn L. Browning a,⇑ , Liv S.E. Damgaard a , Randi Nordström b , Samantha Micciulla c , Saskia Bucciarelli d , Martin Malmsten a,b a Department of Pharmacy, University of Copenhagen, DK-2100 Copenhagen, Denmark b Department of Pharmacy, University of Uppsala, SE-75123 Uppsala, Sweden c Institut Laue-Langevin, 38000 Grenoble, France d Department of Drug Design and Pharmacology, University of Copenhagen, DK-2100 Copenhagen, Denmark graphical abstract article info Article history: Received 5 October 2018 Revised 29 November 2018 Accepted 2 December 2018 Available online 3 December 2018 Keywords: Lipid membrane Neutron reflectometry Oxidative stress Polyunsaturation X-ray scattering abstract The exposure of biological membranes to reactive oxygen species (ROS) plays an important role in many pathological conditions such as inflammation, infection, or sepsis. ROS also modulate signaling processes and produce markers for damaged tissue. Lipid peroxidation, mainly affecting polyunsaturated phospho- lipids, results in a complex mixture of oxidized products, which may dramatically alter membrane prop- erties. Here, we have employed a set of biophysical and surface-chemical techniques, including neutron and X-ray scattering, to study the structural, compositional, and stability changes due to oxidative stress on phospholipid bilayers composed of lipids with different degrees of polyunsaturation. In doing so, we obtained real-time information about bilayer degradation under in situ UV exposure using neutron reflec- tometry. We present a set of interrelated physicochemical effects, including gradual increases in area per molecule, head group and acyl chain hydration, as well as bilayer thinning, lateral phase separation, and defect formation leading to content loss upon membrane oxidation. Such effects were observed to https://doi.org/10.1016/j.jcis.2018.12.007 0021-9797/Ó 2018 Elsevier Inc. All rights reserved. Abbreviations: APM, area per molecule; DLS, dynamic light scattering; FTIR-ATR, Fourier transform infrared spectroscopy with attenuated total reflection; LDL, low- density lipoprotein; LUV, large unilamellar vesicles; OxPL, oxidized phospholipids; MLV, multilamellar vesicles; MS, mass spectrometry; NMR, nuclear magnetic resonance; NR, neutron reflectometry; PAPC, 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine; PC, phosphatidylcholine; PL, phospholipid; POPC, 1-palmitoyl-2-oleoyl-sn- glycero-3-phosphocholine; PUFA, polyunsaturated fatty acid; ROS, reactive oxygen species; SAXS, small-angle X-ray scattering; SUV, small unilamellar vesicles; TBARS, thiobarbituric acid reactive species; UV, ultraviolet light; WAXS, wide-angle X-ray scattering. ⇑ Corresponding authors at: Department of Pharmacy, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark. E-mail addresses: elisa.parra@sund.ku.dk (E. Parra-Ortiz), kathryn.browning@sund.ku.dk (K.L. Browning), liv.damgaard@sund.ku.dk (L.S.E. Damgaard), randi.nordstrom@- farmaci.uu.se (R. Nordström), micciulla@ill.fr (S. Micciulla), saskia.bucciarelli@sund.ku.dk (S. Bucciarelli), martin.malmsten@sund.ku.dk (M. Malmsten). Journal of Colloid and Interface Science 538 (2019) 404–419 Contents lists available at ScienceDirect Journal of Colloid and Interface Science journal homepage: www.elsevier.com/locate/jcis