| 1. |
- Agmo Hernández, Víctor
(author)
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An overview of surface forces and the DLVO theory
- 2023
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In: ChemTexts. - : Springer. - 2199-3793. ; 9:4
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Journal article (peer-reviewed)abstract
- This lecture text focuses on surface forces and interactions in a liquid medium, with particular emphasis on the surface-surface interactions described by the DLVO theory, i.e., van der Waals attraction and electric double-layer repulsion. The text begins by describing the fundamental forces of nature, their connection to intermolecular interactions, and how the latter result in measurable forces between surfaces and macroscopical objects. A step-by-step reasoning on how DLVO forces arise is then presented, accompanied by a simplified description of the mathematical derivations of the main equations within the framework of the theory. The connection between the DLVO theory and the prediction of the stability of colloidal systems is presented. Examples on how the colloidal stability can be controlled or tuned are presented. The shortcomings of the original DLVO theory are discussed, and recent extended models dealing with these issues are briefly described. The text closes with a general overview of some of the most relevant non-DLVO interaction.
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| 2. |
- Agmo Hernández, Víctor, et al.
(author)
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Electrochemistry of Adhesion and Spreading of Lipid Vesicles on Electrodes
- 2013
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In: Applications of Electrochemistry in Medicine. - Boston, MA : Springer US. - 9781461461487 ; , s. 189-247
-
Book chapter (other academic/artistic)abstract
- Biological membranes have developed to separate different compartments of organisms and cells. There is a large number of rather different functions which membranes have to fulfil: (1) they control the material and energy fluxes of metabolic processes, (2) they provide a wrapping protecting the compartments from chemical and physical attacks of the environment, (3) they provide interfaces at which specific biochemical machineries can operate (e.g., membrane bound enzymes), (4) they are equipped for signal transduction, (5) they possess the necessary stability and flexibility to allow cell division, and endo- and exocytosis as well as migration, (6) they present anchoring structures that enable cell-to-cell and cell-to-matrix physical interactions and intercellular communication. These are certainly not all functions of membranes as new functionalities are continuously reported. Since the biological membranes separate essentially aqueous solutions, such separating borders—if they should possess a reasonable stability and also flexibility combined with selective permeability—have to be built up of hydrophobic molecules exposing to both sides a similar interface. It was one of the most crucial and most lucky circumstances for the development and existence of life that certain amphiphilic molecules are able to assemble in bilayer structures (membranes), which—on one side—possess a rather high physical and chemical stability, and—on the other side—are able to incorporate foreign molecules for modifying both the physical properties as well as the permeability of the membranes for defined chemical species. The importance of the chemical function of membranes and all its constituents, e.g., ion channels, pore peptides, transport peptides, etc., is generally accepted. The fluid-mosaic model proposed by Singer and Nicolson [1] is still the basis to understand the biological, chemical, and physical properties of biological membranes. The importance of the purely mechanical properties of membranes came much later into the focus of research. The reasons are probably the dominance of biochemical thinking and biochemical models among biologists and medical researchers, as well as a certain lack of appropriate methods to probe mechanical properties of membranes. The last decades have changed that situation due to the development of techniques like the Atomic Force Microscopy, Fluorescence Microscopy, Micropipette Aspiration, Raman Microspectroscopy, advanced Calorimetry, etc. This chapter is aimed at elucidating how the properties of membranes can be investigated by studying the interaction of vesicles with a very hydrophobic surface, i.e., with the surface of a mercury electrode. This interaction is unique as it results in a complete disintegration of the bilayer membrane of the vesicles and the formation of an island of adsorbed lipid molecules, i.e., a monolayer island. This process can be followed by current-time measurements (chronoamperometry), which allow studying the complete disintegration process in all its details: the different steps of that disintegration can be resolved on the time scale and the activation parameters can be determined. Most interestingly, the kinetics of vesicle disintegration on mercury share important features with the process of vesicle fusion and, thus, sheds light also on mechanisms of endocytosis and exocytosis. Most importantly, not only artificial vesicles (liposomes) can be studied with this approach, but also reconstituted plasma membrane vesicles and even intact mitochondria. Hence, one can expect that the method may provide in future studies also information on the membrane properties of various other vesicles, including exosomes, and may allow investigating various aspects of drug action in relation to membrane properties (transmembrane transport, tissue targeting, bioavailability, etc.), and also the impact of pathophysiological conditions (e.g., oxidative modification) on membrane properties, on a hitherto not or only hardly accessible level.
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| 3. |
- Agmo Hernández, Víctor, et al.
(author)
-
Enhanced interpretation of adsorption data generated by liquid chromatography and by modern biosensors
- 2013
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In: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1317, s. 22-31
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Journal article (peer-reviewed)abstract
- In this study we demonstrate the importance of proper data processing in adsorption isotherm estimations. This was done by investigating and reprocessing data from five cases on two closely related platforms: liquid chromatography (LC) and biosensors. The previously acquired adsorption data were reevaluated and reprocessed using a three-step numerical procedure: (i) preprocessing of adsorption data, (ii) adsorption data analysis and (iii) final rival model fit. For each case, we will discuss what we really measure and what additional information can be obtained by numerical processing of the data. These cases clearly demonstrate that numerical processing of LC and biosensor data can be used to gain deeper understanding of molecular interactions with adsorption media. This is important because adsorption data, especially from biosensors, is often processed using old and simplified methods. (C) 2013 Elsevier B.V. All rights reserved.
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| 4. |
- Agmo Hernández, Víctor, et al.
(author)
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Intrinsic Heterogeneity in Liposome Suspensions Caused by the Dynamic Spontaneous Formation of Hydrophobic Active Sites in Lipid Membranes
- 2011
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:8, s. 4873-4883
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Journal article (peer-reviewed)abstract
- The spontaneous, dynamic formation of hydrophobic active sites in lipid bilayer membranes is studied and characterized. It is shown that the rates of formation and consumption of these active sites control at least two important properties of liposomes: their affinity for hydrophobic surfaces and the rate by which they spontaneously release encapsulated molecules. The adhesion and spreading of liposomes onto hydrophobic polystyrene nanoparticles and the spontaneous leakage of an encapsulated fluorescent dye were monitored for different liposome compositions employing Cryo-TEM, DLS, and fluorescence measurements. It was observed that an apparently homogeneous, monodisperse liposome suspension behaves as if composed by two different populations: a fast leaking population that presents affinity for the hydrophobic substrate employed, and a slow leaking population that does not attach immediately to it. The results reported here suggest that the proportion of liposomes in each population changes over time until a dynamic equilibrium is reached. It is shown that this phenomenom can lead to irreproducibility in, for example, spontaneous leakage experiments, as extruded liposomes leak much faster just after preparation than 24 h afterward. Our findings account for discrepancies in several experimental results reported in the literature. To our knowledge, this is the first systematic study addressing the issue of an existing intrinsic heterogeneity of liposome suspensions.
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| 5. |
- Agmo Hernández, Víctor, et al.
(author)
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Label-Free Characterization of Peptide-Lipid Interactions Using Immobilized Lipodisks
- 2013
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In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 85:15, s. 7377-7384
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Journal article (peer-reviewed)abstract
- Lipodisks, planar lipid bilayer structures stabilized by PEG-ylated lipids, were in the present study covalently bound and immobilized onto sensors for quartz crystal microbalance with dissipation monitoring (QCM-D) studies. It is shown that the modified sensors can be used to characterize the interaction of lipodisks with α-helical amphiphilic peptides with an accuracy similar to that obtained with well established fluorimetric approximations. The method presented has the great advantage that it can be used with peptides in their native form even if no fluorescent residues are present. The potential of the method is illustrated by determining the parameters describing the association of melittin, mastoparan X, and mastoparan with immobilized lipodisks. Both thermodynamic and kinetic analyses are possible. The presented method constitutes a useful tool for fundamental studies of peptide–membrane interactions and can also be applied to optimize the design of lipodisks, for example, for sustained release of antimicrobial peptides in therapeutic applications.
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| 6. |
- Agmo Hernández, Víctor, et al.
(author)
-
Ubiquinone-10 alters mechanical properties and increases stability of phospholipid membranes
- 2015
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In: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 0005-2736 .- 1879-2642. ; 1848:10, s. 2233-2243
-
Journal article (peer-reviewed)abstract
- Abstract Ubiquinone-10 is mostly known for its role as an electron and proton carrier in aerobic cellular respiration and its function as a powerful antioxidant. Accumulating evidence suggest, however, that this well studied membrane component could have several other important functions in living cells. The current study reports on a previously undocumented ability of ubiquinone-10 to modulate the mechanical strength and permeability of lipid membranes. Investigations of DPH fluorescence anisotropy, spontaneous and surfactant induced leakage of carboxyfluorescein, and interactions with hydrophobic and hydrophilic surfaces were used to probe the effects caused by inclusion of ubiquinone-10 in the membrane of phospholipid liposomes. The results show that ubiquinone in concentrations as low as 2 mol.% increases the lipid packing order and condenses the membrane. The altered physicochemical properties result in a slower rate of release of hydrophilic components, and render the membrane more resistant towards rupture. As judged from comparative experiments using the polyisoprenoid alcohol solanesol, the quinone moiety is essential for the membrane stabilizing effects to occur. Our findings imply that the influence of ubiquinone-10 on the permeability and mechanical properties of phospholipid membranes is similar to that of cholesterol. The reported data indicate, however, that the molecular mechanisms are different in the two cases.
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| 7. |
- Agmo Hernandez, Victor, et al.
(author)
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Study of the temporal distribution of the adhesion-spreading events of liposomes on a mercury electrode
- 2009
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In: Journal of Solid State Electrochemistry. - : Springer Science and Business Media LLC. - 1432-8488 .- 1433-0768. ; 13:7, s. 1111-1114
-
Journal article (peer-reviewed)abstract
- The formal analysis of the mechanism of adhesion spreading of liposomes at mercury electrodes shares several characteristics with the mechanism of metal nucleation at electrodes. It is shown that the description of the temporal distribution of the adhesion-spreading events is similar to that of the temporal distribution of metal clusters. Both processes are stochastic in nature and can be described by the Poisson distribution. Using this approach, a previously proposed model for the overall adhesion-spreading mechanism, considering the formation of active sites on the liposome and the actual attachment of the liposomes to the mercury surface, is validated.
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| 8. |
- Agmo Hernández, Víctor, 1980-, et al.
(author)
-
The electrochemistry of liposomes
- 2008
-
In: Israel Journal of Chemistry. - 0021-2148. ; 48, s. 169-184
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Review (peer-reviewed)
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| 9. |
- Agmo Hernández, Víctor, et al.
(author)
-
The lipid composition determines the kinetics of adhesion and spreading of liposomes on mercury electrodes
- 2008
-
In: Bioelectrochemistry. - : Elsevier BV. - 1567-5394 .- 1878-562X. ; 74:1, s. 149-156
-
Journal article (peer-reviewed)abstract
- The dependence of membrane properties on their composition was studied by following the adhesion and spreading of unilamellar and multilamellar liposomes on static mercury electrodes with the help of chronoamperometry. The analysis of the peak-shaped signals allows determining the kinetic parameters of the three-step adhesion-spreading process. The presence of cholesterol in the membrane stabilizes the bilayer in the liquid-crystal line phase, and destabilizes the gel phase. The kinetic parameters also show the effect of superlattice formation in the DMPC-cholesterol system. The detergent triton X-100 is only incorporated in the liquid-crystalline DMPC membranes, and it is expelled to the solution when the membrane is transformed to the gel phase. In the liquid-crystalline membrane, it enhances the adhesion-spreading of liposomes on mercury. The lyric peptides mastoparan X and melittin affect the adhesion-spreading in a similar manner. For the rupture-spreading step, their effect is explained by pore formation. The results obtained with lecithins of different length suggest that the bilayer opening process has much in common with flip-flop translocations. For this process the activation energies were found to be independent of the chain length of the lecithin molecules, while the preexponential factor in the Arthenius equation decreases drastically for longer chains.
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| 10. |
- Agmo Hernandez, Victor, et al.
(author)
-
The overall adhesion-spreading process of liposomes on a mercury electrode is controlled by a mixed diffusion and reaction kinetics mechanism
- 2009
-
In: Journal of Solid State Electrochemistry. - : Springer Science and Business Media LLC. - 1432-8488 .- 1433-0768. ; 13:4, s. 639-649
-
Journal article (peer-reviewed)abstract
- Using high-resolution chronoamperometric measurements, with sampling each 1.333 micro s, the initial step of the adhesion-spreading of liposomes on a mercury electrode was studied. These measurements allow getting a deeper insight into the first interaction of the liposomes with the mercury electrode, and they show that the overall adhesion-spreading process at different potentials is partially controlled by a fast but weak interaction equilibrium resulting in a mixed diffusion- and reaction-kinetics-controlled mechanism of the overall reaction.
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| 11. |
- Agmo Hernández, Víctor
(author)
-
The theory of metal electronucleation applied to the study of fundamental properties of liposomes
- 2013
-
In: Journal of Solid State Electrochemistry. - : Springer. - 1432-8488 .- 1433-0768. ; 17:2 (SI), s. 299-305
-
Research review (peer-reviewed)abstract
- This short review describes how the theory of electrochemical metal nucleation considering non-stationary effects due to the activation of latent nucleation sites has been successfully translated and applied to describe phenomena observed on lipid membranes. This rather unexpected connection is merely formal, but has resulted in a completely new approach in liposome research. It has been proposed that hydrophobic active sites spontaneously and constantly appear and disappear on lipid membranes. These sites control the affinity of liposomes for hydrophobic surfaces and determine the permeability of the lipid membrane to small hydrophilic molecules. Thus, the kinetic models for liposome adhesion on hydrophobic substrates and for the spontaneous leakage of liposomal content are identical to that of non-stationary nucleation mentioned above. Therefore, the broad scope of the available work on metal nucleation has facilitated the interpretation of the data obtained in liposome research. Future applications of the nucleation model in the realm of liposomes are also discussed.
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| 12. |
- Duong-Thi, Minh-Dao, et al.
(author)
-
Lipodisks integrated with weak affinity chromatography enable fragment screening of integral membrane proteins
- 2016
-
In: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; 141:3, s. 981-988
-
Journal article (peer-reviewed)abstract
- Membrane proteins constitute the largest class of drug targets but they present many challenges in drug discovery. Importantly, the discovery of potential drug candidates is hampered by the limited availability of efficient methods for screening drug-protein interactions. In this work we present a novel strategy for rapid identification of molecules capable of binding to a selected membrane protein. An integral membrane protein (human aquaporin-1) was incorporated into planar lipid bilayer disks (lipodisks), which were subsequently covalently coupled to porous derivatized silica and packed into HPLC columns. The obtained affinity columns were used in a typical protocol for fragment screening by weak affinity chromatography (WAC), in which one hit was identified out of a 200 compound collection. The lipodisk-based strategy, which ensures a stable and native-like lipid environment for the protein, is expected to work also with other membrane proteins and screening procedures.
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| 13. |
- Duong-Thi, Minh-Dao, et al.
(author)
-
Lipodisks integrated with weak affinity chromatography enable fragment screening of integral membrane proteins
- 2016
-
In: The Analyst. - 0003-2654 .- 1364-5528. ; 141:3, s. 981-988
-
Journal article (peer-reviewed)abstract
- Membrane proteins constitute the largest class of drug targets but they present many challenges in drug discovery. Importantly, the discovery of potential drug candidates is hampered by the limited availability of efficient methods for screening drug-protein interactions. In this work we present a novel strategy for rapid identification of molecules capable of binding to a selected membrane protein. An integral membrane protein (human aquaporin-1) was incorporated into planar lipid bilayer disks (lipodisks), which were subsequently covalently coupled to porous derivatized silica and packed into HPLC columns. The obtained affinity columns were used in a typical protocol for fragment screening by weak affinity chromatography (WAC), in which one hit was identified out of a 200 compound collection. The lipodisk-based strategy, which ensures a stable and native-like lipid environment for the protein, is expected to work also with other membrane proteins and screening procedures.
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| 14. |
- Eriksson, Anna, et al.
(author)
-
Cooperative adsorption behavior of phosphopeptides on TiO2 leads to biased enrichment, detection and quantification
- 2015
-
In: The Analyst. - : Royal Society of Chemistry. - 0003-2654 .- 1364-5528. ; 140:1, s. 303-312
-
Journal article (peer-reviewed)abstract
- The adsorption behavior of phosphopeptides onto TiO2 surfaces was studied using the quartz crystal microbalance with dissipation monitoring (QCM-D) as the main experimental technique. The main focus is the characterization of the emergence of positive cooperativity under conditions where the peptides have a positively charged C-term. It is shown that when carrying no net charge, small water-soluble peptides as a rule develop positive cooperativity. The impact of the adsorption mechanism on the outcome of TiO2 based enrichment methods was investigated with the help of matrix assisted laser desorption-ionization mass spectrometry (MALDI-MS). The data presented illustrate how the phosphopeptide profile in the enriched material may deviate from that in the native sample, as cooperative phosphopeptides are overrepresented in the former. Furthermore, commonly employed washing and elution solutions may facilitate preferential release of certain peptides, leading to further bias in the recovered sample. Taken together, the results of the present study demonstrate that thorough understanding of the mechanisms behind the adsorption of phosphopeptides on the enrichment material is necessary in order to develop reliable qualitative and quantitative methods for phosphoproteomics.
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| 15. |
- Eriksson, Anna I. K., 1984-
(author)
-
Enrichment and Separation of Phosphorylated Peptides on Titanium Dioxide Surfaces : Applied and Fundamental Studies
- 2013
-
Doctoral thesis (other academic/artistic)abstract
- Protein phosphorylation is a very common posttranslational modification (PTM), which lately has been found to hold the keyrole in the development of many severe diseases, including cancer. Thereby, phosphoprotein analysis tools, generally based on specific enrichment of the phosphoryl group, have been a hot topic during the last decade.In this thesis, two new TiO2-based on-target enrichment methods are developed and presented together with enlightening fundamental results.Evaluation of the developed methods was performed by the analysis of: custom peptides, β-casein, drinking milk, and the viral protein pIIIa. The results show that: i) by optimizing the enrichment protocol (first method), new phosphorylated peptides can be found and ii) by the addition of a separation step after the enrichment (second method), more multi-phosphorylated peptides, which usually are hard to find, could be detected. The fundamental part, on the other hand, shows that the phosphopeptide adsorption is caused by electrostatic interactions, in general follows the Langmuir model, and the affinity increases with the phosphorylation degree. Here, however, the complexity of the system was also discovered, as the adsorption mechanism was found to be affected by the amino acid sequence of the phosphopeptide.
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| 16. |
- Eriksson, Anna, et al.
(author)
-
Mesoporous TiO2-Based Experimental Layout for On-Target Enrichment and Separation of Multi- and Monophosphorylated Peptides Prior to Analysis with Matrix-Assisted Laser Desorption-Ionization Mass Spectrometry
- 2011
-
In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 83:3, s. 761-766
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Journal article (peer-reviewed)abstract
- A simple method for on-target enrichment and subsequent separation and analysis of phosphorylated peptides is presented. The tryptic digest of a phosphorylated protein, in this case beta-casein, is loaded onto a spot on a thin stripe made of mesoporous TiO2 sintered onto a conductive glass surface. After washing with a salicylic buffer in order to remove the nonphosphorylated peptides, the stripe is placed in an elution chamber containing a phosphate solution. In a way analogous to thin layer chromatography (TLC), the phosphate solution acts as an eluent, clearly separating multi- and monophosphorylated peptides. By performing matrix-assisted laser desorption-ionization mass spectrometry (MALDI-MS) along the stripe, the detection of all phosphorylated peptides present in the digest is facilitated, as they are isolated from each other. The method was also tested on commercial drinking milk, achieving successful separation between multi- and monophosphorylated peptides, as well as a detection limit in the femtomole range. As the enrichment, separation, and analysis take place in the same substrate, sample handling and risk of contamination and sample loss is minimized. The results obtained suggest that the method, once optimized, may successfully provide a complete phosphoproteome.
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| 17. |
- Eriksson, Anna, et al.
(author)
-
On-target titanium dioxide-based enrichment for characterization of phosphorylations in the Adenovirus pIIIa protein
- 2013
-
In: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1317:SI, s. 105-109
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Journal article (peer-reviewed)abstract
- A recently developed titanium dioxide (TiO2) based on-target method for phosphopeptide enrichment and matrix assisted laser desorption-ionization mass spectrometry (MALDI MS) analysis was used to investigate phosphorylations in the Adenovirus type 2 structural protein pIIIa. Lysates of purified virus particles were separated on 1-D SDS-PAGE and the band for the pIIIa protein was excised for tryptic digestion into peptides that were enriched with the on-target method. The enrichment provided by the method clearly improved the detectability of phosphorylated peptides and the results show for the first time evidence for multi-phosphorylated peptides in pIIIa. Moreover, three novel phosphorylations were identified in the protein sequence, even though the precise positions could not be determined. These results illustrate the potential of the method for the characterization of novel phosphoproteomes in biological samples of medical relevance.
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| 18. |
- Eriksson, Anna, et al.
(author)
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Optimized Protocol for On-Target Phosphopeptide Enrichment Prior to Matrix-Assisted Laser Desorption-Ionization Mass Spectrometry Using Mesoporous Titanium Dioxide
- 2010
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In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 82:11, s. 4577-4583
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Journal article (peer-reviewed)abstract
- A novel on-target phosphopeptide enrichment method is presented that allows specific enrichment and direct analysis by matrix assisted laser desorption-ionization mass spectrometry (MALDI-MS) of phosphorylated peptides. Spots consisting of a thin film of anatase titanium dioxide are sintered onto a conductive glass surface. Enrichment and analysis can be performed on the modified target with minimal sample handling. The protocol leads to an enrichment efficiency that is superior to what has been reported before for similar methods. The method was tested using beta-casein as a model phosphorylated protein as well as with a custom peptide mixed with its phosphorylated form. A very low detection limit, a significantly improved phosphoprofiling capability, and a simple experimental approach provide a powerful tool for the enrichment, detection, and analysis of phosphopeptides.
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| 19. |
- Eriksson, Anna, et al.
(author)
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Physicochemical Characterization of Phosphopeptide/Titanium Dioxide Interactions Employing the Quartz Crystal Microbalance Technique
- 2013
-
In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 117:7, s. 2019-2025
-
Journal article (peer-reviewed)abstract
- The rapidly growing field of phosphoproteomics has led to a strong demand for procedures enabling fast and reliable isolation and enrichment of phosphorylated proteins and peptides. During the past decade, several novel phosphopeptide enrichment methods based on the affinity of phosphoryl groups for titanium dioxide (TiO2) have been developed and tested. The ultimate goal of obtaining comprehensive phosphoproteomes has, however, been found difficult to achieve and the obtained results often vary, dependent on the enrichment method and protocol used. In the present study, the physical chemistry of the phosphopeptide binding to TiO2 is investigated by means of measurements using a quartz crystal microbalance with dissipation monitoring (QCM-D). Special emphasis is put on the effect of the degree of phosphorylation of the phosphopeptide, the impact of the primary amino acid structure, and the role of electrostatic interactions. The results show that, in general, adsorption of phosphopeptides follows the Langmuir model and that the affinity for the TiO2 surface increases in a nonlinear fashion with increasing degree of phosphorylation. An exception was detected, however, where positive cooperativity between the peptides existed and the Langmuir model no longer applied. The source behind the cooperativity could be traced back to the primary amino acid structure and, more specifically, the presence of positively charged amino acids in positions that enable electrostatic interaction with phosphoryl groups on neighboring peptides. Regardless of the net peptide charge, the TiO2–phosphopeptide interaction was for all phosphopeptides investigated found to be mainly of electrostatic origin. This study highlights and explains some of the most common problems with the TiO2-based enrichment methods used today.
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| 20. |
- Eriksson, Emma K., et al.
(author)
-
Choice of cuvette material can influence spectroscopic leakage and permeability experiments with liposomes.
- 2018
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In: Chemistry and Physics of Lipids. - : Elsevier BV. - 0009-3084 .- 1873-2941. ; 215, s. 63-70
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Journal article (peer-reviewed)abstract
- Liposome solute permeability experiments are widely performed to gain information about lipid membrane characteristics. Spectroscopic methods are often used for this purpose, usually monitoring the leakage of a self-quenching fluorescent dye (e.g., carboxyfluorescein, CF) from the liposomes. Hereby, we investigate the effect of liposome-cuvette interactions, a seldom considered detail, on the results obtained from liposomal permeability experiments. The spontaneous leakage of CF from liposomes with different surface properties and phase states is followed using quartz and polystyrene cuvettes, and the results are compared. It is shown that for most lipid compositions the leakage profiles vary notably between different cuvette materials. Reproducibility of the measurements also varies depending on the cuvettes used, with polystyrene providing with more robust results. To explain these observations, the interaction of liposomes with polystyrene and quartz-like surfaces was characterized with the help of the quartz crystal microbalance with dissipation monitoring (QCM-D). Our results show that, while liposomes seldom interact with polystyrene, quartz-liposome interactions are almost unavoidable and have a large impact on the leakage experiments mainly via two mechanisms: i) the rupturing of liposomes on the cuvette surface causing a fast release of encapsulated CF, and ii) the disruption of adsorbed liposomes caused by magnetic stirring. Depending on their composition, the liposomes interact in different ways with quartz, affecting thus the extent of each proposed mechanism. The experiments demonstrate the importance of considering the cuvette material when planning and conducting spectroscopic experiments with liposomes.
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| 21. |
- Eriksson, Emma K., et al.
(author)
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Effect of ubiquinone-10 on the stability of biomimetic membranes of relevance for the inner mitochondrial membrane.
- 2018
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In: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 0005-2736 .- 1879-2642. ; 1860:5, s. 1205-1215
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Journal article (peer-reviewed)abstract
- Ubiquinone-10 (Q10) plays a pivotal role as electron-carrier in the mitochondrial respiratory chain, and is also well known for its powerful antioxidant properties. Recent findings suggest moreover that Q10 could have an important membrane stabilizing function. In line with this, we showed in a previous study that Q10 decreases the permeability to carboxyfluorescein (CF) and increases the mechanical strength of 1-palmitoyl-2-oleyl-sn-glycero-phosphocholine (POPC) membranes. In the current study we report on the effects exerted by Q10 in membranes having a more complex lipid composition designed to mimic that of the inner mitochondrial membrane (IMM). Results from DPH fluorescence anisotropy and permeability measurements, as well as investigations probing the interaction of liposomes with silica surfaces, corroborate a membrane stabilizing effect of Q10 also in the IMM-mimicking membranes. Comparative investigations examining the effect of Q10 and the polyisoprenoid alcohol solanesol on the IMM model and on membranes composed of individual IMM components suggest, moreover, that Q10 improves the membrane barrier properties via different mechanisms depending on the lipid composition of the membrane. Thus, whereas Q10's inhibitory effect on CF release from pure POPC membranes appears to be directly and solely related to Q10's lipid ordering and condensing effect, a mechanism linked to Q10's ability to amplify intrinsic curvature elastic stress dominates in case of membranes containing high proportions of palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE).
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| 22. |
- Eriksson, Emma K.
(author)
-
Effects of Ubiquinone-10 on the Stability and Mechanical Properties of Lipid Membranes
- 2018
-
Doctoral thesis (other academic/artistic)abstract
- Ubiquinones are a group of fat-soluble molecules present in many biological membranes. The most abundant version in humans, ubiquinone-10 (Q10), plays an important role in the mitochondrial respiration chain and also functions as a powerful antioxidant. Accumulating evidence suggests that Q10 also could have other functions in the membrane. The aim of this thesis has been to explore Q10’s possible role as a membrane stabilizer.To investigate the potential effect of Q10 in membranes, liposomes with compositions of biological relevance were used as models systems. In lipid systems mimicking that of the inner membrane of the mitochondria, Q10 was found to lower the membrane’s permeability to hydrophilic solutes, render the membrane more resistant to rupturing and promote membrane lipid order. In models mimicking the plasma membrane of E.coli, Q10 was observed to decrease the water permeability and increase the elastic resistance against membrane deformation during osmotic shock. All in all, the results suggest a general membrane stabilizing effect of Q10. The results indicate, however, that the extent of, as well as the mechanisms behind, the membrane stabilizing effects of Q10 vary depending on the membrane lipid composition. Part of the reason for this can likely be traced back to differences in the intermembrane location of Q10.Supplementary experiments, which facilitated the investigations of Q10 membrane effects, revealed that the choice of cuvette material was of importance for liposome leakage experiments with fluorescent hydrophilic dyes. The results of these experiments highlight the need to take liposome-cuvette interactions into account when planning and evaluating spectroscopic studies involving liposomes.
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| 23. |
- Eriksson, Emma K., et al.
(author)
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Osmoprotective effect of ubiquinone in lipid vesicles modelling the E. coli plasma membrane
- 2019
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In: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 0005-2736 .- 1879-2642. ; 1861:7, s. 1388-1396
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Journal article (peer-reviewed)abstract
- Bacteria need to be able to adapt to sudden changes in their environment, including drastic changes in the surrounding osmolarity. As part of this adaptation, the cells adjust the composition of their cytoplasmic membrane. Recent studies have shown that ubiquinones, lipid soluble molecules involved in cell respiration, are overproduced by bacteria grown in hyperosmotic conditions and it is thus believed that these molecules can provide with osmoprotection. Hereby we explore the mechanisms behind these observations. Liposomes with a lipid headgroup composition mimicking that of the cytoplasmic membrane of E. coli are used as suitable models. The effect of ubiquinone-10 (Q10) on water transport across the membranes is characterized using a custom developed fluorescence-based experimental approach to simultaneously determine the membrane permeability coefficient and estimate the elastic resistance of the membrane towards deformation. It is shown that both parameters are affected by the presence of ubiquinone-10. Solanesol, a molecule similar to Q10 but lacking the quinone headgroup, also provides with osmoprotection although it only improves the resistance of the membrane against deformation. The fluorescence experiments are complemented by cryogenic transmission electron microscopy studies showing that the E. coli membrane mimics tend to flatten into spheroid oblate structures when osmotically stressed, suggesting the possibility of lipid segregation. In agreement with its proposed osmoprotective role, the flattening process is hindered by the presence of Q10.
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| 24. |
- Forooqi Motlaq, Vahid, et al.
(author)
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Dissolution mechanism of supported phospholipid bilayer in the presence of amphiphilic drug investigated by neutron reflectometry and quartz crystal microbalance with dissipation monitoring
- 2022
-
In: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier. - 0005-2736 .- 1879-2642. ; 1864:10
-
Journal article (peer-reviewed)abstract
- The influence and interaction of the ionizable amphiphilic drug amitriptyline hydrochloride (AMT) on a 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) phospholipid bilayer supported on a silica surface have been investigated using a combination of neutron reflectometry and quartz crystal microbalance with dissipation monitoring. Adding AMT solutions with concentrations 3, 12, and 50 mM leaves the lipid bilayer mainly intact and we observe most of the AMT molecules attached to the head-group region of the outer bilayer leaflet. Virtually no AMT penetrates into the hydrophilic head-group region of the inner leaflet close to the silica surface. By adding 200 mM AMT solution, the lipid bilayer dissolved entirely, indicating a threshold concentration for the solubilization of the bilayer by AMT. The observed threshold concentration is consistent with the observation that various bilayer structures abruptly transform into mixed AMT-DOPC micelles beyond a certain AMT-DOPC composition. Based on our experimental observations, we suggest that the penetration of drug into the phospholipid bilayer, and subsequent solubilization of the membrane, follows a two-step mechanism with the outer leaflet being removed prior to the inner leaflet.
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| 25. |
- Grad, Philipp, et al.
(author)
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A closer look at calcium-induced interactions between phosphatidylserine-(PS) doped liposomes and the structural effects caused by inclusion of gangliosides or polyethylene glycol- (PEG) modified lipids
- 2024
-
In: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier. - 0005-2736 .- 1879-2642. ; 1866:2
-
Journal article (peer-reviewed)abstract
- The effects of polyethylene glycol- (PEG) modified lipids and gangliosides on the Ca2+ induced interaction between liposomes composed of palmitoyl-oleoyl phosphatidylethanolamine (POPE) and palmitoyl-oleoyl phosphatidylserine (POPS) was investigated at physiological ionic strength. Förster resonance energy transfer (FRET) studies complemented with dynamic light scattering (DLS) and cryo-transmission electron microscopy (Cryo-EM) show that naked liposomes tend to adhere, rupture, and collapse on each other's surfaces upon addition of Ca2+, eventually resulting in the formation of large multilamellar aggregates and bilayer sheets. Noteworthy, the presence of gangliosides or PEGylated lipids does not prevent the adhesion-rupture process, but leads to the formation of small, long-lived bilayer fragments/disks. PEGylated lipids seem to be more effective than gangliosides at stabilizing these structures. Attractive interactions arising from ion correlation are proposed to be a driving force for the liposome-liposome adhesion and rupture processes. The results suggest that, in contrast with the conclusions drawn from previous solely FRET-based studies, direct liposome-liposome fusion is not the dominating process triggered by Ca2+ in the systems studied.
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| 26. |
- Grad, Philipp, et al.
(author)
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Adhesion and Structural Changes of PEGylated LipidNanocarriers on Silica Surfaces
- 2021
-
In: PhysChem. - Basel, Switzerland : MDPI. - 2673-7167. ; 1:2, s. 133-151
-
Journal article (peer-reviewed)abstract
- PEGylated lipid nanoparticles have a continuously expanding range of applications,particularly within pharmaceutical areas. Hereby, it is shown with the help of the Quartz CrystalMicrobalance with Dissipation monitoring (QCM-D) and other surface sensitive techniques that, atroom temperature, PEGylated liposomes and lipodisks adhere strongly to silica surfaces resultingin the displacement of the hydration layer of silica and the formation of immobilized nanoparticlefilms. Furthermore, it is shown that drastic changes in the structure of the immobilized films occurif the temperature is increased to >35 ◦C. Thus, intact immobilized PEGylated liposomes ruptureand spread, even in the gel phase state; immobilized lipodisks undergo complete separation of theircomponents (bilayer forming lipids and PEGylated lipids) resulting in a monolayer of adsorbedPEGylated lipids; and PEGylated supported lipid bilayers release part of the water trapped betweenthe lipid membrane and the surface. It is hypothesized that these changes occur mainly due to thechanges in the configuration of PEG chains and a drastic decrease of the affinity of the polymer forwater. The observed phenomena can be applied, e.g., for the production of defect-free supportedlipid bilayers in the gel or liquid ordered phase states.
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| 27. |
- Grad, Philipp, et al.
(author)
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Avoiding artifacts in liposome leakage measurements via cuvette- and liposome-surface modifications
- 2022
-
In: Journal of liposome research. - : Taylor & Francis Group. - 0898-2104 .- 1532-2394. ; 32:3, s. 237-249
-
Journal article (peer-reviewed)abstract
- The barrier properties of lipid membranes are often determined by investigating their solute permeability with the help of spectroscopic methods and the use of liposome-encapsulated self-quenching fluorescent dyes, for example, Carboxyfluorescein (CF). It was shown previously that liposome-surface interactions, and thus the choice of cuvette material, influence the result of such spectroscopic permeability/leakage experiments. In this work, we explore different methods to minimize the artifacts observed in spontaneous leakage measurements performed with cholesterol-containing liposomes. The spontaneous leakage of CF from liposomes with different composition and surface properties is monitored in cuvettes composed of quartz, polystyrene (PS), and Poly(methyl methacrylate) (PMMA). Our results show that significantly different leakage profiles are recorded for the exact same liposome batch depending on the cuvette material used. Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) experiments indicate that these discrepancies likely arise from side processes occurring at the solution-cuvette interface, mainly, the attaching and spreading of liposomes. Further, we show that in some cases it is possible to minimize liposome-cuvette interactions, and reduce the experimental artifacts, by supplementing the liposomes with polyethylene glycol (PEG)-grafted lipids or gangliosides, and/or by pre-adsorbing free PEG to the cuvette walls. The collected data suggest that quartz cuvettes modified by adsorption of PEG8000 are suitable for spontaneous leakage experiments with POPC:cholesterol-based liposomes, while other cuvette materials perform poorly in the same experiments.
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| 28. |
- Grad, Philipp, et al.
(author)
-
Improved accuracy and reproducibility of spontaneous liposome leakage measurements by the use of supported lipid bilayer-modified quartz cuvettes
- 2023
-
In: Colloids and Surfaces B. - : Elsevier. - 0927-7765 .- 1873-4367. ; 221
-
Journal article (peer-reviewed)abstract
- Recent studies have revealed avid interactions between liposomes and several solid materials, such as quartz, polystyrene (PS) and poly(methyl methacrylate) (PMMA), commonly found in cuvettes used for spectroscopic measurements. These interactions risk leading to detrimental changes in liposome structure and integrity that, if overlooked, may compromise the measurements. In case of leakage experiments based on probing the spontaneous release of encapsulated hydrophilic markers, the liposome-cuvette interactions may result in the recording of erroneously high degrees of leakage. In the present study we investigate the possibilities of preventing unwanted liposome-cuvette interactions through the use of quartz cuvettes passivated with supported lipid bilayers (SLBs). The results show that this strategy leads to higher reproducibility and significantly improved accuracy of the leakage measurements. The usefulness of the method is validated in comparative experiments focused on how changes in temperature and lipid phase state, as well as inclusion of poly(ethylene glycol)-conjugated lipids (PEG-lipids), affect the release of liposome encapsulated carboxyfluorescein (CF).
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| 29. |
- Hellberg, D, et al.
(author)
-
Kinetics of liposome adhesion on a mercury electrode
- 2005
-
In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 109, s. 14715-14726
-
Journal article (peer-reviewed)abstract
- The adhesion of liposomes on a mercury electrode leads to capacitive signals due to the formation of islands of lecithin monolayers. Integration of the current-time transients gives charge-time transients that can be fitted by the empirical equation Q(t) = Q(0) + Q(1)(1 - exp(-t/tau(1))) + Q(2)(1 - exp(-t/tau(2))), where the first term on the right side is caused by the docking of the liposome on the mercury surface, the second term is caused by the opening of the liposome, and the third term is caused by the spreading of the lecithin island on the mercury surface. The temperature dependence of the two time constants tau(1) and tau(2) and the temperature dependence of the overall adhesion rate allow determination of the activation energies of the opening, the spreading, and the overall adhesion process both for gel-phase 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and for liquid-crystalline-phase DMPC liposomes. In all cases, the spreading is the rate-determining process. Negative apparent activation energies for the spreading and overall adhesion process of liquid-crystalline-phase DMPC liposomes can be explained by taking into account the weak adsorption equilibria of the intact liposomes and the opened but not yet spread liposomes. A formal kinetic analysis of the reaction scheme supports the empirical equation used for fitting the charge-time transients. The developed kinetic model of liposome adhesion on mercury is similar to kinetic models published earlier to describe the fusion of liposomes. The new approach can be used to probe the stability of liposome membranes.
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| 30. |
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| 31. |
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| 32. |
- Hernandez, Victor Agmo, et al.
(author)
-
Kinetics of the adhesion of DMPC liposomes on a mercury electrode. Effect of lamellarity, phase composition, size and curvature of liposomes, and presence of the pore forming peptide Mastoparan X
- 2006
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 22, s. 10723-10731
-
Journal article (peer-reviewed)abstract
- Liposomes suspended in aqueous electrolyte solutions can adhere at mercury electrodes. The adhesion is a complex process that starts with the docking and opening and leads to a spreading, finally resulting in the formation of islands of adsorbed lecithin molecules. The adhesion process can be followed by chronoamperometry, and a detailed analysis of the macroscopic and microscopic kinetics can be performed yielding rate constants and activation parameters. By using giant unilamellar liposomes and multilamellar liposomes, the effect of lamellarity and liposome size could be elucidated for liposomes in the liquid crystalline, gel, and superlattice phase states. Below the phase transition temperature, the time constant of opening of the liposomes (i.e., the irreversible binding of the lecithin molecules on the preliminary contact interface liposome vertical bar mercury and the therewith associated disintegration of the liposome membrane on that spot) is shown to be strongly size dependent. The activation energy, however, of that process is size independent with the exception of very small liposomes. That size dependence of time constants is a result of the size dependence of the initial contact area. The time constant and the activation energies of the spreading step exhibit a strong size dependence, which could be shown to be due to the size dependence of rate and activation energy of pore formation. Pore formation is necessary to release the solution included in the liposomes. This understanding was corroborated by addition of the pore inducing peptide Mastoparan X to the liposome suspension. The obtained results show that electrochemical studies of liposome adhesion on mercury electrodes can be used as a biomimetic tool to understand the effect of membrane properties on vesicle fusion.
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| 33. |
- Hernandez, Victor Agmo, et al.
(author)
-
One redox probe (dmfc) can drive the transfer of anions and cations across the aqueous electrolyte ionic liquid interface
- 2006
-
In: Electrochemistry communications. - : Elsevier BV. - 1388-2481 .- 1873-1902. ; 8, s. 967-972
-
Journal article (peer-reviewed)abstract
- Three-phase electrodes consisting of droplets of 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate containing decamethylferrocenium (dmfc(+)) cations, immobilized on the surface of graphite electrodes and immersed in aqueous electrolyte solutions have been employed to study the redox driven transfer of anions and cations. Very surprisingly, it has been observed that anions as well as cations can be transferred with one redox probe (dmfc/dmfc(+)) because the Gibbs energies of ion transfer of the different ions are rather similar. (C) 2006 Elsevier B.V. All rights reserved.
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| 34. |
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| 35. |
- Hernandez, Victor Agmo, et al.
(author)
-
The adhesion and spreading of thrombocyte vesicles on electrode surfaces
- 2008
-
In: Bioelectrochemistry. - : Elsevier BV. - 1567-5394 .- 1878-562X. ; 74, s. 210-216
-
Journal article (peer-reviewed)abstract
- The interaction of thrombocyte vesicles with the surface of metal electrodes, i.e., mercury, gold and gold electrodes modified with self assembled monolayers (SAM), was studied with the help of chronoamperometry, atomic force microscopy, and quartz crystal microbalance measurements. The experimental results show that the interaction of the thrombocyte vesicles with the surface of the electrodes depends on the hydrophobicity of the latter: whereas on very hydrophobic surfaces (mercury and gold functionalized with SAM) the thrombocyte vesicles disintegrate and form a monolayer of lipids. on the less hydrophobic gold surface a bilayer is formed. The chronoamperometric measurements indicate the possibility of future applications to probe membrane properties of thrombocytes. (C) 2008 Elsevier B.V. All rights reserved.
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| 36. |
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| 37. |
- Lundsten, Sara, et al.
(author)
-
Tumor-Targeted Delivery of the p53-Activating Peptide VIP116 with PEG-Stabilized Lipodisks
- 2020
-
In: Nanomaterials. - : MDPI AG. - 2079-4991. ; 10:4
-
Journal article (peer-reviewed)abstract
- Stapled peptides targeting the interaction between p53 and its negative regulators MDM2 and MDM4 have exhibited great potential as anti-cancer drugs, albeit with room for improvement in formulation and tumor specificity. Lipid bilayer disks (lipodisks) have emerged as promising drug nanocarriers and can by attachment of targeting moieties be directed selectively towards tumor cells. Tumor-targeted delivery of stapled peptides by use of lipodisks may therefore increase the uptake in the tumors and limit toxicity in healthy tissue. Here, we utilized epidermal growth factor receptor (EGFR)-targeted lipodisks to deliver p53-activating stapled peptide VIP116 to EGFR-expressing tumor cells. We demonstrate that VIP116 can be stably formulated in lipodisks (maximum peptide/lipid molar ratio 0.11). In vitro cell studies verify specific binding of EGF-decorated lipodisks to tumor cells and confirm that targeted delivery of VIP116 significantly decreases tumor cell viability.
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| 38. |
- Meiby, Elinor, et al.
(author)
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Immobilized lipodisks as model membranes in high-throughput HPLC-MS analysis
- 2013
-
In: Analytical and Bioanalytical Chemistry. - : Springer Science and Business Media LLC. - 1618-2642 .- 1618-2650. ; 405:14, s. 4859-4869
-
Journal article (peer-reviewed)abstract
- Lipodisks, also referred to as polyethylene glycol (PEG)-stabilized bilayer disks, have previously been demonstrated to hold great potential as model membranes in drug partition studies. In this study, an HPLC-MS system with stably immobilized lipodisks is presented. Functionalized lipodisks were immobilized on two different HPLC support materials either covalently by reductive amination or by streptavidin-biotin binding. An analytical HPLC column with immobilized lipodisks was evaluated by analysis of mixtures containing 15 different drug compounds. The efficiency, reproducibility, and stability of the system were found to be excellent. In situ incorporation of cyclooxygenase-1 (COX-1) in immobilized lipodisks on a column was also achieved. Specific binding of COX-1 to the immobilized lipodisks was validated by interaction studies with QCM-D. These results, taken together, open up the possibility of studying ligand interactions with membrane proteins by weak affinity chromatography.
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| 39. |
- Morin Zetterberg, Malin, et al.
(author)
-
Optimization of lipodisk properties by modification of the extent and density of the PEG corona
- 2016
-
In: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 484, s. 86-96
-
Journal article (peer-reviewed)abstract
- Lipodisks are nanosized flat, circular, phospholipid bilayers that are edge-stabilized by polyethylene glycol-conjugated lipids (PEG-lipids). Over the last decade, lipodisks stabilized with PEG of molecular weight 2000 or 5000 have been shown to hold high potential as both biomimetic membranes and drug carriers. In this study we investigate the possibilities to optimize the properties of the lipodisks, and widen their applicability, by reducing the PEG molecular weight and/or the density of the PEG corona. Results obtained by cryo-transmission electron microscopy and dynamic light scattering show that stable, well-defined lipodisks can be produced from mixtures of distearoylphosphatidylcholine (DSPC) and distearoylphosphatidylethanolamine conjugated to PEG of molecular weight 1000 (DSPE-PEG(1000)). Preparations based on the use of DSPE-PEG(750) tend, in contrast, to be polydisperse in size and structure. By comparing immobilization of lipodisks stabilized with DSPE-PEG(1000), DSPE-PEG(2000), and DSPE-PEG(5000) to porous and smooth silica surfaces, we show that the amount of surface bound disks can be considerably improved by the use of PEG-lipids with reduced molecular weight. Further, a modified preparation protocol that enables production of lipodisks with very low PEG-lipid content is described. The reduced PEG density, which facilitates the incorporation of externally added ligand-linked PEG-lipids, is shown to be beneficial for the production of targeting lipodisks.
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| 40. |
- Mårtensson, Christoffer, et al.
(author)
-
Ubiquinone-10 in gold-immobilized lipid membrane structures acts as a sensor for acetylcholine and other tetraalkylammonium cations
- 2012
-
In: Bioelectrochemistry. - Amsterdam : Elsevier. - 1567-5394 .- 1878-562X. ; 88, s. 171-180
-
Journal article (peer-reviewed)abstract
- It is reported that the reduction of ubiquinone incorporated into supported lipid bilayers and into immobilized liposome layers on gold electrodes is kinetically and thermodynamically enhanced by the presence of acetylcholine and tetrabutylammonium (TBA+) in solution. The reduction peak and the mid-peak potentials of the redox reactions, determined by cyclic voltammetry, are displaced towards more positive potentials by approximately 500 and 250 mV, respectively, in the case of TBA+; and by approximately 750 and 530 mV, respectively, in the case of acetylcholine. The intensity of the signal varies with the cation concentration, allowing for quantitative determinations in the millimolar range. It is proposed that the enhanced reduction of ubiquinone arises from the formation of tetraalkylammonium cation–ubiquinone radical anion ion-pairs. Electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) measurements confirmed that the potential shift and the intensity of the redox signal are coupled with the adsorption of the tetraalkylammonium cations on the lipid membrane. The Langmuir adsorption equilibrium constant (K) of TBA+ on lipid membranes at physiological pH is determined. In supported lipid bilayers K = 440.7 ± 160 M− 1, while in an immobilized liposome layer K = 35.53 ± 3.53 M− 1.
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| 41. |
- Norling, Karin, 1988, et al.
(author)
-
Gel Phase 1,2-Distearoyl-sn-glycero-3-phosphocholine-Based Liposomes Are Superior to Fluid Phase Liposomes at Augmenting Both Antigen Presentation on Major Histocompatibility Complex Class II and Costimulatory Molecule Display by Dendritic Cells in Vitro
- 2019
-
In: ACS Infectious Diseases. - : American Chemical Society (ACS). - 2373-8227. ; 5:11, s. 1867-1878
-
Journal article (peer-reviewed)abstract
- Lipid-based nanoparticles have in recent years attracted increasing attention as pharmaceutical carriers. In particular, reports of them having inherent adjuvant properties combined with their ability to protect antigen from degradation make them suitable as vaccine vectors. However, the physicochemical profile of an ideal nanoparticle for vaccine delivery is still poorly defined. Here, we used an in vitro dendritic cell assay to assess the immunogenicity of a variety of liposome formulations as vaccine carriers and adjuvants. Using flow cytometry, we investigated liposome-assisted antigen presentation as well as the expression of relevant costimulatory molecules on the cell surface. Cytokine secretion was further evaluated with an enzyme-linked immunosorbent assay (ELISA). We show that liposomes can successfully enhance antigen presentation and maturation of dendritic cells, as compared to vaccine fusion protein (CTA1-3E alpha-DD) administered alone. In particular, the lipid phase state of the membrane was found to greatly influence the vaccine antigen processing by dendritic cells. As compared to their fluid phase counterparts, gel phase liposomes were more efficient at improving antigen presentation. They were also superior at upregulating the costimulatory molecules CD80 and CD86 as well as increasing the release of the cytokines IL-6 and IL-1 beta. Taken together, we demonstrate that gel phase liposomes, while nonimmunogenic on their own, significantly enhance the antigen-presenting ability of dendritic cells and appear to be a promising way forward to improve vaccine immunogenicity.
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| 42. |
- Quentel, Francois, et al.
(author)
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Studying ion transfers across a room temperature ionic liquid vertical bar aqueous electrolyte interface driven by redox reactions of lutetium bis(tetra-tert-butylphthalocyaninato)
- 2007
-
In: JOURNAL OF ELECTROANALYTICAL CHEMISTRY. - 1572-6657. ; 611, s. 192-200
-
Journal article (peer-reviewed)abstract
- Ion transfer reactions across the interface between an aqueous electrolyte solution and the room temperature ionic liquid (RTIL) 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([hmim][fap]) were studied with the help of three-phase electrodes. The electrode assembly comprised an edge plane pyrolytic graphite electrode modified with a thin layer of [hmim][fap] containing lutetium bis(tetra-tert-butylphthalocyaninato) (Lu[tBu(4)Pc](2)) as redox probe. Lu[tBu(4)Pc]2 can be oxidized and reduced to a stable hydrophobic monovalent cation and anion, respectively, hence allowing investigation of the transfer of cations and anions in one and the same voltammetric experiment. In spite of the strong hydrophobicity of the salt [hmim][fap], the electrode reactions of he redox probe studied in contact with various inorganic aqueous electrolytes, were frequently accompanied by expulsion of ions constituting the RTIL into the aqueous phase. Using ion chromatography it was found that the distribution of ions in the aqueous electrolyte/RTIL biphasic system is strongly determined by ion exchange reactions. The affinity of the ions of the RTIL for the aqueous phase was assessed using the water-nitrobenzene (W-NB) system, and the following Gibbs energies of ion transfer were found: Delta(W–>NB) G([hmim]+)(circle minus) = -16.6 +/- 0.9 kJ mol(-1) and Delta(W-NB) G([fap]-)(circle minus) 22.4 +/- 0.3 kJ mol(-1). (C) 2007 Elsevier B.V. All rights reserved.
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| 43. |
- Ravandeh, M., et al.
(author)
-
A combination of electrochemistry and mass spectrometry to monitor the interaction of reactive species with supported lipid bilayers
- 2020
-
In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10
-
Journal article (peer-reviewed)abstract
- Reactive oxygen and nitrogen species (RONS), e.g. generated by cold physical plasma (CPP) or photodynamic therapy, interfere with redox signaling pathways of mammalian cells, inducing downstream consequences spanning from migratory impairment to apoptotic cell death. However, the more austere impact of RONS on cancer cells remains yet to be clarified. In the present study, a combination of electrochemistry and high-resolution mass spectrometry was developed to investigate the resilience of solid-supported lipid bilayers towards plasma-derived reactive species in dependence of their composition. A 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid bilayer was undisturbed by 200 µM H2O2 (control) but showed full permeability after CPP treatment and space-occupying oxidation products such as PoxnoPC, PAzePC, and POPC hydroperoxide were found. Electron paramagnetic resonance spectroscopy demonstrated the presence of hydroxyl radicals and superoxide anion/hydroperoxyl radicals during the treatment. In contrast, small amounts of the intramembrane antioxidant coenzyme Q10 protected the bilayer to 50% and LysoPC was the only POPC derivative found, confirming the membrane protective effect of Q10. Such, the lipid membrane composition including the presence of antioxidants determines the impact of pro-oxidant signals. Given the differences in membrane composition of cancer and healthy cells, this supports the application of cold physical plasma for cancer treatment. In addition, the developed model using the combination of electrochemistry and mass spectrometry could be a promising method to study the effect of reactive species or mixes thereof generated by chemical or physical sources.
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| 44. |
- Reijmar, Karin, et al.
(author)
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Characterizing and controlling the loading and release of cationic amphiphilic peptides onto and from PEG-stabilized lipodisks
- 2016
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 32:46, s. 12091-12099
-
Journal article (peer-reviewed)abstract
- Recent studies have identified PEG-stabilized lipid nanodisks (lipodisks) as promising carriers for cationic amphiphilic peptides with antimicrobial and anticancer activity. Using fluorimetric and nanogravimetric methods, we have in this work characterized the parameters describing and controlling the binding of three selected peptides (melittin, LL37, and magainin 2) onto lipodisks. It was found that the affinity of melittin for lipodisks is independent of the disk size and rim charge. On the other hand, the number of binding sites is strongly dependent on both parameters, with the highest loading being obtained for small disks with a negatively charged rim. An optimized composition of the lipodisks was utilized to study the loading of antimicrobial peptides magainin 2 and human LL37. It was observed that although magainin 2 can be loaded in large amounts, it is released very fast upon dilution, which limits future therapeutic applications. In contrast, LL37 can be loaded at relevant concentrations and the formulation is stable. This opens up for applications of LL37-loaded lipodisks as antibiotics and in anticancer treatments.
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