Name: assembly of cell mimicking supported and suspended lipid bilayer models for the study of molecular interactions
Uploaded: 2021-08-03T13:00:00
Description: Watch this Scientific Journal Video about Assembly of Cell Mimicking Supported and Suspended Lipid Bilayer Models for the Study of Molecular Interactions at JoVE.com

This material is based upon work supported by the National Science Foundation under Grant No. 1942418 awarded to A.S., and a National Science Foundation Graduate Research Fellowship awarded to C.M.B.H., under Grant No. 1644760. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. The authors thank Dr. Noel Vera-Gonz&#225;lez for lipid vesicle characterization data acquisition. The authors thank Professor Robert Hurt (Brown University) for the use of his Zetasizer. The authors thank the Brown University Mass Spectrometry Facility, in particular, Dr. Tun-Li Shen for assistance with quantifying lipid composition.

1. Developing uni-lipid vesicles
<ol>
	<li>Thin-film hydration method
	<ol>
		<li>Preparation and storage of lipid stock solutions 
		NOTE: All steps using chloroform need to be performed in a chemical fume hood. Chloroform should always be pipetted using solvent safe carbon fiber pipette tips. Solutions containing chloroform should always be stored in glass vials.
		<ol>
			<li>Prepare a 10 mg/mL lipid stock solution by adding the appropriate volume of chloroform into the vial containing the lipid powder and mix ...

This protocol allows for the formation of lipid vesicles, supported lipid bilayers, and suspended lipid bilayers. Here, critical steps are presented to form each of these structures. When forming lipid vesicles, it is important to extrude above the transition temperature of the lipid39. When below the transition temperature, the lipid is physically present in its ordered gel phase39. In this ordered phase the hydrocarbon lipid tails are fully extended allowing for close pac...

The cell membrane, composed primarily of phospholipids, cholesterol, and proteins, is a crucial component of all living cells1. With organization driven by lipid amphiphilicity, the cell membrane functions as a protective barrier and regulates how the cell interacts with its surrounding environment2. Several cellular processes are dependent on the lipid and protein composition of the membrane1,2. For example, cell membrane interactions are important for effective drug delivery3. Pharmaceuticals, biologics, nanomaterials, biological toxins, and environmental toxicants can impact the integrity of a cell membrane, thereby affecting cellular function4. The construction of in vitro cell mimicking membrane models based on the lipid composition of cell membranes has the potential to provide facile tools to greatly enhance the study of the potential impact of these materials on cells.
Model lipid bilayers include lipid vesicles, supported lipid bilayers, and suspended lipid bilayers. Supported lipid bilayers are a model of the phospholipid cell membrane commonly used in biotechnology applications where lipid vesicles are ruptured on a supported substrate material5,6,7,8,9. One common technique used to monitor bilayer formation is quartz crystal microbalance with dissipation monitoring (QCM-D), which examines the adsorption of vesicles in comparison to the bulk liquid properties in situ8,10,11,12,13,14. Previously, QCM-D has been used to demonstrate that under flow conditions, once a critical vesicle coverage of phosphatidylcholine (PC) lipid vesicles is achieved on the surface, they spontaneously rupture into rigid lipid bilayers15. Previous work has also investigated supported lipid bilayer formation with varying lipid compositions16, incorporation of lipid proteins17,18,19, and utilizing polymer cushions20, yielding supported lipid bilayers capable of mimicking various aspects of cell membrane function.
Lipid bilayers have been used to mimic various biological barriers from sub-cellular to organ levels including mitochondrion, red blood cell, and liver cell membranes by altering the phospholipid, cholesterol, and glycolipid components21. These more complex multi-lipid vesicles may require additional methods to achieve vesicle rupture, depending on the lipid composition. For example, previous studies have utilized an &#945;-helical (AH) peptide derived from the hepatitis C virus&#39;s nonstructural protein 5A to induce bilayer formation by destabilizing the adsorbed lipid vesicles22,23. Using this AH peptide, supported lipid bilayers mimicking placental cells have previously been formed24. The great potential of supported lipid bilayers for biomedical applications has been demonstrated with investigations spanning molecular and nanoparticle transport25, 26, environmental toxicant interactions27, protein assembly and function17,18,19, peptide arrangement and insertion28, 29, drug screening30, and microfluidic platforms31.
Suspended lipid bilayers have been used for pharmaceutical screening studies via a parallel artificial membrane permeability assay (PAMPA) where a lipid bilayer is suspended across a porous hydrophobic insert32,33,34,35. PAMPA lipid models have been developed for different biological interfaces including the blood-brain, buccal, intestinal, and transdermal interfaces36. By combining both the supported lipid bilayer and PAMPA techniques, adsorption, permeability, and embedment of compounds within lipid components of a desired tissue or cell type can be thoroughly studied.
This protocol describes the fabrication and application of in vitro cell membrane lipid bilayer models to investigate several molecular interactions. Preparation of both uni-lipid and multi-lipid supported and suspended lipid bilayers is detailed. To form a supported lipid bilayer, lipid vesicles are first developed using thin-film hydration and extrusion methods followed by physicochemical characterization. Formation of a supported lipid bilayer using QCM-D monitoring and fabrication of suspended lipid membranes for use in PAMPA is discussed. Finally, multi-lipid vesicles for the development of more complex cell mimicking membranes are examined. Using both types of fabricated lipid membranes, this protocol demonstrates how this tool can be used to study molecular interactions. Overall, this technique constructs cell mimicking lipid bilayers with high reproducibility and versatility.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1-palmitoyl-2-oleoyl-glycero-3-phosphocholine&#160; (POPC, 16:0-18:1 PC)</td>
			<td>Avanti Polar Lipids</td>
			<td>850457</td>
			<td></td>
		</tr>
		<tr>
			<td>1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (sodium salt) (POPS, 16:0-18:1 PS)</td>
			<td>Avanti Polar Lipids</td>
			<td>840034</td>
			<td></td>
		</tr>
		<tr>
			<td>1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (16:0-18:1 PE)</td>
			<td>Avanti Polar Lipids</td>
			<td>850757</td>
			<td></td>
		</tr>
		<tr>
			<td>1,2-dioleoyl-sn-glycero-2-phospho-L-serine (DOPS, 18:1 PS)</td>
			<td>Avanti Polar Lipids</td>
			<td>840035</td>
			<td></td>
		</tr>
		<tr>
			<td>1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC, 18:1 (&#916;9-Cis) PC)</td>
			<td>Avanti Polar Lipids</td>
			<td>850375</td>
			<td></td>
		</tr>
		<tr>
			<td>1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE, 18:1 (&#916;9-Cis) PE)</td>
			<td>Avanti Polar Lipids</td>
			<td>850725</td>
			<td></td>
		</tr>
		<tr>
			<td>1,2-distearoyl-sn-glycero-3-ethylphosphocholine (chloride salt) (18:0 EPC (Cl Salt))</td>
			<td>Avanti Polar Lipids</td>
			<td>890703</td>
			<td></td>
		</tr>
		<tr>
			<td>3 mL Luer-Loc syringes</td>
			<td>BD</td>
			<td>309657</td>
			<td></td>
		</tr>
		<tr>
			<td>40 mL sample vial, amber with polytetrafluoroethylene (PTFE)/rubber liner</td>
			<td>Duran Wheaton Kimble</td>
			<td>W224605</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetonitrile</td>
			<td>Sigma-Aldrich</td>
			<td>271004</td>
			<td></td>
		</tr>
		<tr>
			<td>Alconox</td>
			<td>Fisher Scientific</td>
			<td>50-821-781</td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonium formate</td>
			<td>Millipore Sigma</td>
			<td>LSAC70221</td>
			<td></td>
		</tr>
		<tr>
			<td>C18, 3.5 um x 50 mm column, SunFire</td>
			<td>Waters</td>
			<td>&#160;186002551</td>
			<td></td>
		</tr>
		<tr>
			<td>Chloroform</td>
			<td>Millipore Sigma</td>
			<td>LSAC288306</td>
			<td></td>
		</tr>
		<tr>
			<td>Cuvette UV Micro LCH 8.5 mm, 50 um, RPK</td>
			<td>Sarstedt</td>
			<td>67.758.001</td>
			<td></td>
		</tr>
		<tr>
			<td>Di(2-ethylhexyl) phthalate (DEHP)</td>
			<td>Millipore Sigma</td>
			<td>36735</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide (DMSO)</td>
			<td>Millipore Sigma</td>
			<td>LSAC472301</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Pharmco</td>
			<td>111000200</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter supports, 10 mm</td>
			<td>Avanti Polar Lipids</td>
			<td>610014</td>
			<td>Size for mini extruder</td>
		</tr>
		<tr>
			<td>Folded capillary zeta cell</td>
			<td>Malvern Panalytical</td>
			<td>DTS1070</td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropanol</td>
			<td>Sigma-Aldrich</td>
			<td>190764-4L</td>
			<td></td>
		</tr>
		<tr>
			<td>Kimwipes</td>
			<td>Kimberly Clark</td>
			<td>34256</td>
			<td></td>
		</tr>
		<tr>
			<td>L-&#945;-phosphatidylinositol (soy) (Soy PI)</td>
			<td>Avanti Polar Lipids</td>
			<td>840044</td>
			<td></td>
		</tr>
		<tr>
			<td>L-&#945;-phosphitidylcholine (Egg, Chicken)</td>
			<td>Avanti Polar Lipids</td>
			<td>840051</td>
			<td></td>
		</tr>
		<tr>
			<td>LiposoFast &#174; LF-50</td>
			<td>Avestin, Inc.</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Sigma-Aldrich</td>
			<td>179337 - 4L</td>
			<td></td>
		</tr>
		<tr>
			<td>Mini-extruder set with holder/heating block</td>
			<td>Avanti Polar Lipids</td>
			<td>610000</td>
			<td></td>
		</tr>
		<tr>
			<td>MultiScreen-IP Filter Plate, 0.45&#160;&#181;m, clear, sterile</td>
			<td>Millipore Sigma</td>
			<td>MAIPS4510</td>
			<td>for PAMPA studies</td>
		</tr>
		<tr>
			<td>Nitrogen gas, ultrapure</td>
			<td>TechAir</td>
			<td>NI T5.0</td>
			<td></td>
		</tr>
		<tr>
			<td>Nuclepore hydrophilic membranes, polycarbonate, 19 mm, 0.1 um</td>
			<td>Whatman</td>
			<td>800309</td>
			<td>Size for mini extruder</td>
		</tr>
		<tr>
			<td>Nuclepore hydrophilic membranes, polycarbonate, 25 mm, 0.1 um</td>
			<td>Whatman</td>
			<td>110605</td>
			<td>Size for large extruder</td>
		</tr>
		<tr>
			<td>Parafilm</td>
			<td>Bemis</td>
			<td>PM999</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate buffer saline (PBS), 10x</td>
			<td>Genesee Scienfitic</td>
			<td>25-507X</td>
			<td>Dilute to 1x</td>
		</tr>
		<tr>
			<td>Qsoft 401 software</td>
			<td>Biolin Scientific</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Quartz Crystal Microbalance with Dissipation Q-Sense Analyzer</td>
			<td>Biolin Scientific</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Scintillation vials, borosilicate glass vials, 20 mL</td>
			<td>Duran Wheaton Kimble</td>
			<td>986561</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicon Dioxide, thin QSensors</td>
			<td>Biolin Scientific</td>
			<td>QSX 303</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride (NaCl)</td>
			<td>Millipore Sigma</td>
			<td>LSACS5886</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium dodecyl sulfate (SDS)</td>
			<td>Fisher Scientific</td>
			<td>BP166-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Solvent Safe pipette tips</td>
			<td>Sigma-Aldrich</td>
			<td>S8064</td>
			<td></td>
		</tr>
		<tr>
			<td>Sphingomyelin (Egg, Chicken)</td>
			<td>Avanti Polar Lipids</td>
			<td>860061</td>
			<td></td>
		</tr>
		<tr>
			<td>Trizma base</td>
			<td>Millipore Sigma</td>
			<td>LSACT1503</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-ethylenediaminetretaacetic acid</td>
			<td>Caisson Labs</td>
			<td>TRL01-6X100ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Whatman drain disc, 25 mm</td>
			<td>Whatman</td>
			<td>230600</td>
			<td>Size for large extruder</td>
		</tr>
		<tr>
			<td>Zetasizer ZS90</td>
			<td>Malvern Panalytical</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Zetasizer 7.01 software</td>
			<td>Malvern Panalytical</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

assembly of cell mimicking supported and suspended lipid bilayer models for the study of molecular interactions

Model cell membranes are a useful screening tool with applications ranging from early drug discovery to toxicity studies. The cell membrane is a crucial protective barrier for all cell types, separating the internal cellular components from the extracellular environment. These membranes are composed largely of a lipid bilayer, which contains outer hydrophilic head groups and inner hydrophobic tail groups, along with various proteins and cholesterol. The composition and structure of the lipids themselves play a crucial role in regulating biological function, including interactions between cells and the cellular microenvironment, which may contain pharmaceuticals, biological toxins, and environmental toxicants. In this study, methods to formulate uni-lipid and multi-lipid supported and suspended cell mimicking lipid bilayers are described. Previously, uni-lipid phosphatidylcholine (PC) lipid bilayers as well as multi-lipid placental trophoblast-inspired lipid bilayers were developed for use in understanding molecular interactions. Here, methods for achieving both types of bilayer models will be presented. For cell mimicking multi-lipid bilayers, the desired lipid composition is first determined via lipid extraction from primary cells or cell lines followed by liquid chromatography-mass spectrometry (LC-MS). Using this composition, lipid vesicles are fabricated using a thin-film hydration and extrusion method and their hydrodynamic diameter and zeta potential are characterized. Supported and suspended lipid bilayers can then be formed using quartz crystal microbalance with dissipation monitoring (QCM-D) and on a porous membrane for use in a parallel artificial membrane permeability assay (PAMPA), respectively. The representative results highlight the reproducibility and versatility of in vitro cell membrane lipid bilayer models. The methods presented can aid in rapid, facile assessment of the interaction mechanisms, such as permeation, adsorption, and embedment, of various molecules and macromolecules with a cell membrane, helping in the screening of drug candidates and prediction of potential cellular toxicity.

This protocol details methods for forming supported and suspended lipid bilayers (Figure 1). The first step to forming a supported lipid bilayer is to develop lipid vesicles. The mini extruder allows for small volumes of lipid vesicles to be prepared (1 mL or less), while the large extruder allows for 5-50 mL of lipid vesicles to be prepared in one batch. Size distributions of uni-lipid vesicles formed by either the mini or large extruder are shown in Figure 2A....

Watch this Scientific Journal Video about Assembly of Cell Mimicking Supported and Suspended Lipid Bilayer Models for the Study of Molecular Interactions at JoVE.com

Assembly of Cell Mimicking Supported and Suspended Lipid Bilayer Models for the Study of Molecular Interactions

This protocol describes the formation of cell mimicking uni-lipid and multi-lipid vesicles, supported lipid bilayers, and suspended lipid bilayers. These in vitro models can be adapted to incorporate a variety of lipid types and can be used to investigate various molecule and macromolecule interactions.

Model cell membranes are a useful screening tool with applications ranging from early drug discovery to toxicity studies. The cell membrane is a crucial ...

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