Cholesterol solubility limit in lipid membranes probed by small angle neutron scattering and MD simulations

Garg, Sumit; Castro-Roman, Francisco; Porcar, Lionel; Butler, Paul; Bautista, Pedro Jesus; Krzyzanowski, Natalie; Perez-Salas, Ursula

doi:10.1039/c4sm01219d

Cited by 23 publications

(22 citation statements)

References 26 publications

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“…Excess cholesterol can induce severe coronary pathology with the narrowing of the inner blood vessel walls through the deposition of plaques containing cholesterol crystals, which is due to the solubility limit of cholesterol into lipids. A recent SANS study performed on lipid contrast matched conditions to isolate the scattering coming from the cholesterol [ 64 ] inserted in a POPC or POPS liposome, has revealed a molar fraction solubility limit of 61% and 73% of cholesterol in POPC and POPS, respectively. Further, no evidence of stable nanodomains of cholesterol in POPS membranes was found, as suggested in other reports.…”

Section: Sans For the Characterization Of Liposome Nanocarriersmentioning

confidence: 99%

Small Angle X-ray and Neutron Scattering: Powerful Tools for Studying the Structure of Drug-Loaded Liposomes

2016

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Nanovectors, such as liposomes, micelles and lipid nanoparticles, are recognized as efficient platforms for delivering therapeutic agents, especially those with low solubility in water. Besides being safe and non-toxic, drug carriers with improved performance should meet the requirements of (i) appropriate size and shape and (ii) cargo upload/release with unmodified properties. Structural issues are of primary importance to control the mechanism of action of loaded vectors. Overall properties, such as mean diameter and surface charge, can be obtained using bench instruments (Dynamic Light Scattering and Zeta potential). However, techniques with higher space and time resolution are needed for in-depth structural characterization. Small-angle X-ray (SAXS) and neutron (SANS) scattering techniques provide information at the nanoscale and have therefore been largely used to investigate nanovectors loaded with drugs or other biologically relevant molecules. Here we revise recent applications of these complementary scattering techniques in the field of drug delivery in pharmaceutics and medicine with a focus to liposomal carriers. In particular, we highlight those aspects that can be more commonly accessed by the interested users.

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Section: Sans For the Characterization Of Liposome Nanocarriersmentioning

confidence: 99%

Small Angle X-ray and Neutron Scattering: Powerful Tools for Studying the Structure of Drug-Loaded Liposomes

2016

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“…More recently, we found how defects in membrane packing induced by a supporting surface facilitate lipid flip-flop too and methodologies that can potentially have this effect on membranes result in inaccurate measured rates ( 39 ). From the MD side, we have also suggested that the tendency of the simulations to accumulate cholesterol in the bilayer center suggests that the energy barrier to flip is too low ( 46 , 47 ). Further, with TR-SANS, we have demonstrated that although exchange and flip-flop are coupled, it is their interdependence in the movement of lipids between and within membranes that allows for their distinction, even when the most significant contribution in TR-SANS comes from the exchange process as supported by the AIC test.…”

Section: Discussionmentioning

confidence: 94%

Influence of the membrane environment on cholesterol transfer

Breidigan

Krzyzanowski

Liu

et al. 2017

Journal of Lipid Research

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Cholesterol, an essential component in biological membranes, is highly unevenly distributed within the cell, with most localized in the plasma membrane while only a small fraction is found in the endoplasmic reticulum, where it is synthesized. Cellular membranes differ in lipid composition and protein content, and these differences can exist across their leaflets too. This thermodynamic landscape that cellular membranes impose on cholesterol is expected to modulate its transport. To uncover the role the membrane environment has on cholesterol inter- and intra-membrane movement, we used time-resolved small angle neutron scattering to study the passive movement of cholesterol between and within membranes with varying degrees of saturation content. We found that cholesterol moves systematically slower as the degree of saturation in the membranes increases, from a palmitoyl oleyl phosphotidylcholine membrane, which is unsaturated, to a dipalmitoylphosphatidylcholine (DPPC) membrane, which is fully saturated. Additionally, we found that the energetic barrier to move cholesterol in these phosphatidylcholine membranes is independent of their relative lipid composition and remains constant for both flip-flop and exchange at ∼100 kJ/mol. Further, by replacing DPPC with the saturated lipid palmitoylsphingomyelin, an abundant saturated lipid of the outer leaflet of the plasma membrane, we found the rates decreased by a factor of two. This finding is in stark contrast with recent molecular dynamic simulations that predict a dramatic slow-down of seven orders of magnitude for cholesterol flipping in membranes with a similar phosphocholine and SM lipid composition.

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“…To conclude, we reiterate that the proposed hypothesis has already been tested in its basic sense. The published experimental results show that (1) formation of CBDs in liposomal membranes precedes formation of Chol crystals (e.g., [ 17 , 18 , 20 , 30 , 31 ]), and (2) Chol crystals can be formed from membrane Chol (without the external addition of Chol) when the Chol solubility threshold in the membrane is decreased, for example, by lipid peroxidation [ 21 – 23 ]. Based on the saturation recovery EPR technique, we are planning to design an experimental procedure to quantitatively estimate the average amount of Chol in a CBD at the saturation threshold in bilayers made of polyunsaturated phospholipids (before peroxidation).…”

Section: Discussionmentioning

confidence: 99%

“…When the amount of Chol in a membrane exceeds the saturation limit, Chol bilayer domains (CBD) form in the membrane [17]. A further increase of Chol content above the Chol solubility threshold induces formation of Chol crystals [17][18][19][20]. The peroxidation of phospholipids in a membrane containing a large amount of Chol does not change the relative proportion of Chol and phospholipids; however, it lowers the amount of Chol needed for CBDs to start to form [21][22][23].…”

Section: A New Hypothetical Pathway Leading To the Formation Of Cholementioning

confidence: 99%

“…The phase of such a system is classified as a structured liquid-ordered [ 28 ] or dispersed [ 29 ]. When the Chol content in the phospholipid bilayer further increases and exceeds the Chol solubility threshold [ 17 , 18 , 20 , 30 , 31 ], Chol crystals form, presumably outside the membrane [ 31 – 33 ]. Thus, the formation of CBDs precedes the formation of Chol crystals.…”

Section: Evaluation Of the Hypothesismentioning

confidence: 99%

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Hypothetical Pathway for Formation of Cholesterol Microcrystals Initiating the Atherosclerotic Process

Subczynski

Pasenkiewicz-Gierula

2020

Cell Biochem Biophys

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Major factors leading to the development of atherosclerosis are a high cholesterol (Chol) level in the blood and oxidative stress. Both promote the formation of Chol microcrystals in blood vessel walls. Deposition of Chol microcrystals in arterial intima causes inflammation, which initiates and accompanies the atherosclerotic process in all its phases. One of the possible sources of Chol in the blood vessel walls is oxidized low-density lipoproteins—this atherosclerotic plaque formation pathway has already been described in the literature. Here, we hypothesize that initiation of the atherosclerotic process may involve Chol domains in the plasma membranes of arterial cells. Increased Chol content and the presence of polyunsaturated phospholipids in these membranes together with oxidative stress (phospholipid peroxidation) may lead to the formation of pure Chol bilayer domains that, with further peroxidation and increased Chol content, may collapse in the form of Chol seed crystals. Independent of their origin, Chol microcrystals activate inflammasomes, thereby stimulate immune responses, and initiate inflammation that may lead to the development of atherosclerosis. This new, hypothetical pathway has not yet been investigated in depth; however, data from the literature and our own results support its feasibility.

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Cholesterol solubility limit in lipid membranes probed by small angle neutron scattering and MD simulations

Cited by 23 publications

References 26 publications

Small Angle X-ray and Neutron Scattering: Powerful Tools for Studying the Structure of Drug-Loaded Liposomes

Small Angle X-ray and Neutron Scattering: Powerful Tools for Studying the Structure of Drug-Loaded Liposomes

Influence of the membrane environment on cholesterol transfer

Hypothetical Pathway for Formation of Cholesterol Microcrystals Initiating the Atherosclerotic Process

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