| 1. |
- Ali, Sajid, et al.
(författare)
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Dual centrifugation as a novel and efficient method for the preparation of lipodisks
- 2024
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Ingår i: International Journal of Pharmaceutics. - : Elsevier. - 0378-5173 .- 1873-3476. ; 653
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Tidskriftsartikel (refereegranskat)abstract
- Polyethylene glycol (PEG)-stabilized lipodisks have emerged as innovatiive, promising nanocarriers for several classes of drugs. Prior research underscores the important role of lipid composition and preparation method in determining the lipodisk size, uniformity, and drug loading capacity. In this study, we investigate dual centrifugation (DC) as a novel technique for the production of PEG-stabilized lipodisks. Moreover, we explore the potential use of DC for the encapsulation of two model drugs, curcumin and doxorubicin, within the disks. Our results show that by a considerate choice of experimental conditions, DC can be used as a fast and straightforward means to produce small and homogenous lipodisks with a hydrodynamic diameter of 20-30 nm. Noteworthy, the technique works well for the production of both cholesterol-free and cholesterol-containing disks and does not require pre-mixing of the lipids in organic solvent. Furthermore, our investigations confirm the efficacy of DC in formulating curcumin and doxorubicin within these lipodisks. For doxorubicin, careful control and optimization of the experimental conditions resulted in formulations displaying an encouraging encapsulation efficiency of 84 % and a favourable drug-to-lipid ratio of 0.13 in the disks.
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| 2. |
- Brunzell, Ellen, et al.
(författare)
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Investigation of supramolecular structures in various aqueous solutions of an amyloid forming peptide using small-angle X-ray scattering
- 2024
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Ingår i: Soft Matter. - : Royal Society of Chemistry. - 1744-683X .- 1744-6848. ; 20:10, s. 2272-2279
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Tidskriftsartikel (refereegranskat)abstract
- Aggregation of peptide molecules into amyloid fibrils is a characteristic feature of several degenerative diseases. However, the details behind amyloid-formation, and other self-assembled peptide aggregates, remain poorly understood. In this study, we have used small-angle X-ray scattering (SAXS), static and dynamic light scattering (SLS and DLS) as well as cryogenic transmission electron microscopy (cryo-TEM) to determine the structural geometry of self-assembled peptide aggregates in various dilute aqueous solutions. Pramlintide was used as a model peptide to assess the aggregation behaviour of an amyloid-forming peptide. The effects of adding sodium chloride (NaCl), sodium thiocyanate (NaSCN), and sodium fluoride (NaF) and the co-solvent dimethyl sulfoxide (DMSO) on the aggregation behaviour were studied. Our scattering data analysis demonstrates that small oligomeric fibrils aggregate to form networks of supramolecular assemblies with fractal dimensions. The choice of anion in small amounts of added salt has a significant impact on the size of the fibrils as well as on the fractal dimensions of supramolecular clusters. In DMSO the fractal dimension decreased with increasing DMSO concentration, indicating the formation of a less compact structure of the supramolecular assemblies. The peptide pramlintide forms oligomeric species in solution, which make up a supramolecular network characterised by fractal dimensions. The fractal dimension of the network depends on solvent additive.
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| 3. |
- Forooqi Motlaq, Vahid, et al.
(författare)
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Investigation of the enhanced ability of bile salt surfactants to solubilize phospholipid bilayers and form mixed micelles.
- 2021
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Ingår i: Soft Matter. - : Royal Society of Chemistry. - 1744-683X .- 1744-6848. ; 17:33, s. 7769-7780
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Tidskriftsartikel (refereegranskat)abstract
- The self-assembly in mixtures of the anionic bile salt surfactant sodium deoxycholate (NaDC) and the zwitterionic phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) in physiological saline solution has been investigated using light scattering, small-angle X-ray scattering and cryo-transmission electron microscopy. Rather small tri-axial ellipsoidal NaDC-DMPC mixed micelles form at a high content of bile salt in the mixture, which increase in size as an increasing amount of DMPC is incorporated into the micelles. Eventually, the micelles begin to grow substantially in length to form long wormlike micelles. At higher mole fractions of DMPC, the samples become turbid and cryo-TEM measurements reveal the existence of large perforated vesicles (stomatosomes), coexisting with geometrically open disks. To our knowledge, stomatosomes have not been observed before for any bile salt-phospholipid system. Mixed micelles are found to be the sole aggregate structure in a very wide regime of bile salt-phospholipid compositions, i.e. up to about 77 mol% phospholipid in the micelles. This is much higher than the corresponding value of 25 mol% observed for the conventional surfactant hexadecyltrimethylammonium bromide (CTAB) mixed with DMPC in the same solvent. The enhanced ability of bile salt surfactants to solubilize phospholipid bilayers and form mixed micelles is rationalized using bending elasticity theory. From our theoretical analysis, we are able to conclude that amphiphilic molecules rank in the following order of increasing spontaneous curvature: phospholipids < conventional surfactants < bile salts. The bending rigidity of the different amphiphilic molecules increases according to the following sequence: bile salts < conventional surfactants < phospholipids.
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| 4. |
- Forooqi Motlaq, Vahid, et al.
(författare)
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Spontaneous Formation of Ultrasmall Unilamellar Vesicles in Mixtures of an Amphiphilic Drug and a Phospholipid
- 2023
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 39:32, s. 11337-11344
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Tidskriftsartikel (refereegranskat)abstract
- We have observed ultrasmall unilamellar vesicles, withdiametersof less than 20 nm, in mixtures of the tricyclic antidepressant drugamitriptyline hydrochloride (AMT) and the unsaturated zwitterionicphospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) in physiologicalsaline solution. The size and shape of spontaneously formed self-assembledaggregates have been characterized using complementary techniques,i.e., small-angle neutron and X-ray scattering (SANS and SAXS) andcryo-transmission electron microscopy (cryo-TEM). We observe rodlikemixed micelles in more concentrated samples that grow considerablyin length upon dilution, and a transition from micelles to vesiclesis observed as the concentration approaches the critical micelle concentrationof AMT. Unlike the micelles, the spontaneously formed vesicles decreasein size with each step of dilution, and ultrasmall unilamellar vesicles,with diameters as small as about 15 nm, were observed at the lowestconcentrations. The spontaneously formed ultrasmall unilamellar vesiclesmaintain their size for as long we have investigated them (i.e., severalmonths). To the best of our knowledge, such small vesicles have neverbefore been reported to form spontaneously in a biocompatible phospholipid-basedsystem. Most interestingly, the size of the vesicles was observedto be strongly dependent on the chemical structure of the phospholipid,and in mixtures of AMT and the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine(DMPC), the vesicles were observed to be considerably larger in size.The self-assembly behavior in the phospholipid-drug surfactantsystem in many ways resembles the formation of equilibrium micellesand vesicles in mixed anionic/cationic surfactant systems.
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| 5. |
- Grad, Philipp, et al.
(författare)
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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
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Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier. - 0005-2736 .- 1879-2642. ; 1866:2
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Grad, Philipp, et al.
(författare)
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Adhesion and Structural Changes of PEGylated LipidNanocarriers on Silica Surfaces
- 2021
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Ingår i: PhysChem. - Basel, Switzerland : MDPI. - 2673-7167. ; 1:2, s. 133-151
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Grad, Philipp, et al.
(författare)
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Avoiding artifacts in liposome leakage measurements via cuvette- and liposome-surface modifications
- 2022
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Ingår i: Journal of liposome research. - : Taylor & Francis Group. - 0898-2104 .- 1532-2394. ; 32:3, s. 237-249
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Grad, Philipp, et al.
(författare)
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Effect of gangliosides on structure and integrity of polyethylene glycol(PEG)-stabilized liposomes
- 2020
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 578, s. 281-289
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Tidskriftsartikel (refereegranskat)abstract
- The in vivo efficacy and tolerance of polyethylene glycol (PEG)-decorated drug nanocarriers, such as liposomes, is compromised by their tendency to induce the generation of PEG-specific immunoglobulin M (IgM) antibodies. Recently, a number of independent studies have reported on an attenuated anti-PEG immune response upon incorporation of gangliosides in the membrane of PEGylated liposomes. In the present study we investigate the effect of gangliosides on the self-assembled structures found in lipid dispersions based on hydrogenated egg phosphatidylcholine (HEPC), cholesterol and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethyleneglycol)-2000] (DSPE-PEG(2000)). Results from cryo-transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS) investigations show that gangliosides promote structural transitions from liposomes to bilayer disks. In case of samples comprising 5 mol% PEG-conjugated lipids (PEG-lipid), inclusion of 2.5 mol% ganglioside (porcine ganglioside extract) results in the presence of a small but significant amount of disks. With increasing ganglioside content the population of disks grows at the expense of the liposomes. Comparative investigations using isolated ganglioside components reveal that disialoganglioside GD1a is more potent than monosialoganglioside GM1 in promoting disk formation. Experiments involving liposome encapsulated carboxyfluorescein confirm that the ganglioside-induced structural transformations have a detrimental effect on the total entrapped aqueous volume of the samples. The reported coexistence of liposomes and bilayer disks may if overlooked have important implications for the therapeutic efficacy and immunogenicity of ganglioside-supplemented liposomal formulations.
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| 9. |
- Grad, Philipp
(författare)
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Effects of gangliosides and PEG-lipids on the structure, properties and interactions of lipid self-assemblies
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When developing or utilizing lipid-based nanocarriers detailed structural characterization of the lipid self-assemblies, as well as in depth knowledge and control of their interaction with solids materials, is necessary to understand the behaviour. Disregarding one of the parameters can lead to misinterpretation of the results due to non-uniform samples or experimental artifacts caused by undesirable interactions with solid surfaces. Work included in this thesis show that gangliosides promote structural transitions of PEGylated liposomes to bilayer disks. The results suggest that the proposed ability of gangliosides to attenuate the anti-PEG immune response could be coupled to their ability to promote disk-formation.The results of this thesis further emphasize the importance of processes taking place at the solution-solid interface between self-assembled lipid particles and solid surfaces. Silica surfaces were here of particular interest, and the results showed that PEGylated lipid nanocarriers, such as liposomes and lipodisks, spontaneously attach to the material. It was further shown that an elevation of the temperature can lead to irreversible structural changes, such as the formation of supported lipid bilayers. Interestingly, the investigations revealed that defect free supported lipid bilayers (SLB) can be formed from liposomes in the gel phase. The processes at the solution-solid interface are of relevance if the solute permeability of lipid membranes are investigated with the help of liposomes in combination with spectroscopic methods. Experimental artifacts resulting from processes at the solution-cuvette interface affect the measurements and impair the reliability of the results. In order to solve this issue we explored two methods to passivated the cuvette interface, and thus prevent, or minimize, the attractive interactions between the lipid particles and the cuvette walls. In the first case a PEG-polymer and in the second a SLB was used. Both methods have their individual advantages and our findings highlight the importance of a conscious selection of the experimental procedure.
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| 10. |
- Grad, Philipp, et al.
(författare)
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Improved accuracy and reproducibility of spontaneous liposome leakage measurements by the use of supported lipid bilayer-modified quartz cuvettes
- 2023
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Ingår i: Colloids and Surfaces B. - : Elsevier. - 0927-7765 .- 1873-4367. ; 221
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Tidskriftsartikel (refereegranskat)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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