On the Influence of Nucleic Acid Backbone Modifications on Lipid Nanoparticle Morphology.

Nucleic acid therapeutics represent a major advance toward treating diseases at their root cause. However, nucleic acids are prone to degradation by serum endonucleases, clearance through the immune system, and rapid degradation in complex medium. To overcome these barriers, nucleic acids frequently include chemical modifications to improve stability or decrease immune responses.

Measuring molecular order for lipid membrane phase studies: Linear relationship between Laurdan generalized polarization and deuterium NMR order parameter.

Two dimensional phase separation in lipid membranes and cell membranes is of interest to biology because of the idea of membrane rafts - compositionally heterogeneous liquid crystal domains with cellular functions. Few quantitative tools exist for characterizing and differentiating coexisting phases on a molecular scale. Lipid acyl chain order can be measured directly using deuterium nuclear magnetic resonance spectroscopy (H NMR), or inferred using fluorescence microscopy along with the environment-sensitive probe Laurdan.

Lamellar Phases Composed of Phospholipid, Cholesterol, and Ceramide, as Studied by H NMR.

Sphingolipids constitute a significant fraction of cellular plasma membrane lipid content. Among sphingolipids, ceramide levels are usually very low. However, in some cell processes like apoptosis, cell membrane ceramide levels increase markedly because of the activation of enzymes like acid sphingomyelinase.

On the Formation and Morphology of Lipid Nanoparticles Containing Ionizable Cationic Lipids and siRNA.

Lipid nanoparticles (LNPs) containing short interfering RNA (LNP-siRNA) and optimized ionizable cationic lipids are now clinically validated systems for silencing disease-causing genes in hepatocytes following intravenous administration. However, the mechanism of formation and certain structural features of LNP-siRNA remain obscure. These systems are formed from lipid mixtures (cationic lipid, distearoylphosphatidylcholine, cholesterol, and PEG-lipid) dissolved in ethanol that is rapidly mixed with siRNA in aqueous buffer at a pH (pH 4) where the ionizable lipid is positively charged.

The Phase Behavior and Organization of Sphingomyelin/Cholesterol Membranes: A Deuterium NMR Study.

We have studied the dependence of the phase and domain characteristics of sphingomyelin (SM)/cholesterol model membranes on sterol content and temperature using deuterium nuclear magnetic resonance. NMR spectra of N-palmitoyl(D31)-D-erythro-sphingosylphosphorylcholine (PSM-d31) were taken for temperatures from 25 to 70°C and cholesterol concentrations of 0-40%. Analogous experiments were performed using 1-palmitoyl,2-palmitoyl(D31)-sn-glycero-3-phosphocholine (DPPC-d31)/cholesterol membranes to carefully compare the data obtained using palmitoyl chains that have similar "kinked" conformations.

Constrained Versus Free Cholesterol in DPPC Membranes: A Comparison of Chain Ordering Ability Using Deuterium NMR.

We report here the first exploration of the nature of the hydrophobic region of bilayer membranes formed from sterol-modified phospholipids [Huang, Z.; Szoka, F. C.

Effect of Sterol Structure on the Physical Properties of 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine Membranes Determined Using (2)H Nuclear Magnetic Resonance.

The effect of a series of phytosterols on lipid chain ordering in 1-palmitoyl((2)H31)-2-oleoyl-sn-glycero-3-phosphocholine (POPC-d31) multibilayer vesicles was examined by (2)H NMR spectroscopy at 25 °C. These results, along with existing data for other sterols, indicate that the ordering power of sterols in POPC-d31 depends on subtle aspects of sterol structure. Cholesterol, 7-dehydrocholesterol (7-DHC), campesterol, β-sitosterol, ergosterol, brassicasterol, and stigmasterol all increase the lipid chain order as sterol concentration is increased.

Interaction of a charged polymer with zwitterionic lipid vesicles.

The interaction between polyethylenimine (PEI) and phospholipid bilayers plays an important role in several biophysical applications such as DNA transfection of target cells. Despite considerable investigation into the nature of the interaction between PEI and phospholipid bilayers, the physical process remains poorly understood. In this paper, we study the impact of PEI on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) vesicles as a function of salt concentration using several techniques including dynamic (DLS) and static (SLS) light scattering, differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR).

Phase diagrams of lipid mixtures relevant to the study of membrane rafts.

The present paper reviews the phase properties of phosphatidylcholine-sphingomyelin-cholesterol mixtures, that are often used as models for membrane "raft" microdomains. The available data based on X-ray, microscopic and spectroscopic observations, surface pressure and calorimetric measurements, and detergent solubilization assays, are critically evaluated and rationalized in terms of triangular phase diagrams. The remaining uncertainties are discussed specifically and separately from the data on which a consensus appears to exist.

Fluorescent probes alter miscibility phase boundaries in ternary vesicles.

We use 2H NMR to study the effects of probes on the miscibility transition in multilamellar vesicles of di(18:1) phosphatidylcholine (PC; DOPC), chain perdeuterated di(16:0)PC (DPPCd62), and cholesterol both with and without 0.5 mol % of the fluorescent probes DiIC12 and DiOC18. Both probes raise the miscibility transition temperature in dispersions of 1:1 DOPC/DPPCd62 + 30% cholesterol but to differing extents.

Interactions of oleic acid and model stratum corneum membranes as seen by 2H NMR.

We have investigated the mechanism through which the penetration enhancer oleic acid acts on stratum corneum (SC) model membranes (bovine brain ceramide:cholesterol:palmitic acid, 1:1:1 molar ratio). We used solid state deuterium nuclear magnetic resonance to monitor such multilamellar SC dispersions containing either cholesterol-d(6), palmitic acid-d(31), or oleic acid-d(2) as a function of both fatty acid concentration (2:2:1:1 and 1:1:1:1 bovine brain ceramide:cholesterol:palmitic acid:oleic acid) and temperature (18-75 degrees C). Our results show that below 40 degrees C, oleic acid (OA) is in an 'isotropic' phase, indicating that it has not incorporated into the lamellar membrane phase.