| 1. |
- Bartholeyns, J, et al.
(författare)
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Cellular vaccines
- 1998
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Ingår i: Research in Immunology. - 0923-2494 .- 1879-1425. ; 149, s. 647-649
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Tidskriftsartikel (refereegranskat)abstract
- This project is devoted to the development of novel cellular vaccines designed to treat cancer patients. These cellular vaccines present and enhance immunogens, which will elicit a potent immune response. The goal is to achieve safe and effective immune reaction against the patient's own tumour. (1) Autologous cellular vaccines are prepared by processing circulating brood mononuclear cells outside of the patient's body (ex vivo) to differentiate them into antigen-presenting cells (APCs). Monocyte-derived APCs (MD-APCs) are then grown in the presence of exogenous target antigens (tumour cell debris, or apoptotic bodies) to become fully mature APCs. (2) Functionality for antigen presentation to T cells of ex vivo MD-APCs is evaluated in vivo. (3) Cellular vaccines are tested in selected rodent animal models. Efficiency and immune response are monitored in pertinent experimental systems for cancer. Pharmacological data are generated for clinical investigation. Tolerance and biologic effects are documented in primates. (4) The first clinical trials on cancer patients are taking place in 1998 on melanoma and prostate cancer to validate the concept. Specialized eel processors with dedicated software and standardized controls are being developed and used for the preparation of cellular vaccines. (5) The evaluation of new non-viral vectors and the validation of new non-viral transfection methods of mononuclear cells with marker genes is in progress and will lead to the ex vivo transfection of genes coding for immunostimulating cytokines or for tumour antigens in MD-APCs. Efficiency will be validated in vitro and in animal models. The ex vivo and animal model studies validate the clinical relevance of this new cellular immunotechnology. Clinical validation of individual autologous cellular vaccines in specific indications for which no treatment is presently available will allow the development of cellular and gene immunotherapy for other types of cancers.
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| 2. |
- Malmsten, M, et al.
(författare)
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Adsorption of apolipoprotein B at phospholipid model surfaces
- 1995
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 172, s. 485-493
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of apolipoprotein B (Apo B) at a series of surfaces was investigated with in situ ellipsometry. For silica and methylated silica, the adsorbed amount (G), the adsorbed layer thickness (del) and the mean adsorbed layer refractive index (nf) were obtained by a procedure involving studies of the bare substrate at two different ambient refractive indices, as well as four-zone averaging. The adsorbed amount of Apo B is much higher at silica than at methylated silica. Despite this, the adsorbed layer thickness is the same at the two surfaces, and the adsorbed layer formation proceeds similarly. In both cases, the adsorbed layer formation occurs through the adsorption of Apo B molecules in an essentially random orientation, the difference between silica and methylated silica being the number of molecules adsorbed per unit area. Furthermore, the adsorption of Apo B at phospholipid surfaces was investigated. It was found that the adsorption at phosphatidylcholine (PC) was quite limited, whereas that at phosphatidic acid (PA) was substantial. Studies with mixed PA/PC layers showed that the Apo B adsorption depends on the mixed phospholipid layer composition in an essentially linear fashion. Finally, mixed phospholipid layers of PC and ganglioside GM1, as well as phosphatidylinositol (PI) layers, showed a dramatic preferential adsorption of Apo B over, e. g. human serum albumin (HSA), IgG, fibronectin and fibrinogen.
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| 3. |
- Scherlund, M, et al.
(författare)
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Stabilization of a thermosetting emulsion system using ionic and nonionic surfactants
- 1998
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Ingår i: International Journal of Pharmaceutics. - 0378-5173 .- 1873-3476. ; 173, s. 103-116
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Tidskriftsartikel (refereegranskat)abstract
- Ways of achieving a suitable local anesthetic formulation for use in the periodontal cavity were investigated in this study. By choosing poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers as excipients, formulations which are low viscosity fluids at room temperature and rigid elastic gels at body temperature are obtained. Despite the solubilizing capacity of these polymers, formulations containing Lutrol(R) F127 (EO99PO65EO99) and the active ingredients lidocaine and prilocaine at the desired concentrations, i.e. approximately 25 mg g(-1) of each component, are unstable. In order to achieve a more stable formulation a second surfactant can be added to the system since it could help both to solubilize the hydrophobic active ingredients and to stabilize the droplets of lidocaine and prilocaine from flocculation and coalescence. Thus, formulations containing local anesthetic compounds comprising the oil phase, a block copolymer giving the system unique rheological properties, and a suitable second surfactant were evaluated with regard to rheological behavior, drug release properties and stability. The system needs to be balanced regarding the concentration of polymer, active ingredients and surfactant in order to achieve a formulation with suitable properties. Stable formulations with appropriate characteristics for the application in focus here were obtained with anionic, cationic and nonionic surfactants.
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| 4. |
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| 5. |
- Schillén, Karin, et al.
(författare)
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Properties of poly(ethylene oxide)-poly(butylene oxide) diblock copolymers at the interface between hydrophobic surfaces and water
- 1997
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 101, s. 4238-4252
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between molecules of a low molecular weight diblock copolymer of poly(ethylene oxide) (E) and poly(butylene oxide) (B), B8E41, at hydrophobic surfaces were investigated experimentally by using two surface force techniques and ellipsometry. Extended mean-field theory was employed to describe the adsorption of EB diblock copolymers at planar surfaces as well as the forces between surfaces with adsorbed diblock copolymers. It is the hydrophobic poly(butylene oxide) block that anchors the diblock copolymer at the hydrophobic surface with the water-soluble poly(ethylene oxide) block protruding in the aqueous solution in a "brushlike" or at least streched structure. The adsorption kinetics demonstrate that two adsorption regimes exist, one which is transport-limited and the other at higher adsorption where a slower branch due to crowding effects at the surface exists. Only monotonic repulsuve steric forces between the diblock copolymer-coated surfaces were observed in the surface force measurements. The range of the steric repulsion increased with increasing bulk copolymer concentration, whereas the concentration of an inert salt (KBr, up to 0.1 M) did not influence the measured steric interaction. Upon dilution the block copolymer slowly dissolved, which resulted in a less long-range steric force, and under a high force the layers were squeezed out from between the surfaces. The adsorbed layer thickness obtained in the experiments varied with solution volume-to-surface area ratio. This is interpreted as being caused by the polydispersity of the diblock copolymer. The interaction parameters entering the mean-field model were fitted to reproduce adsorption isotherms of the diblock copolymer and of two triblock copolymers of different architectures. Calculations were performed for mondisperse and polydisperse diblock copolymers. The agreement between theory and experiment was improved when the molecular polydispersity (Mm/Mn = 1.1) of the sample was taken into account. In particular, polydispersity led to predicted adsorption isotherms that are more of the high affinity type and more sensitive to low volume-to-surface area ratio and to the interaction between surfaces starting at a longer separation. Among the polymer components, it is those with the largest B block that adsorb preferentially, which leads to an increased amount adsorbed and forces the E chains to adopt more extended conformations.
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| 6. |
- Siegel, G, et al.
(författare)
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Anionic biopolymers as blood flow sensors
- 1996
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Ingår i: Biosensors & bioelectronics. - 0956-5663 .- 1873-4235. ; 11, s. 281-294
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Tidskriftsartikel (refereegranskat)abstract
- The finding of flow-dependent vasodilatation rests on the basic observation that with an increase in blood flow the vessels become wider, with a decrease the vascular smooth muscle cells contract. Proteoheparan sulphate could be the sensor macromolecule at the endothelial cell membrane-blood interface, that reacts on the shear stress generated by the flowing blood, and that informs and regulates the vascular smooth muscle cells via a signal transduction chain. This anionic biopolyelectrolyte possesses viscoelastic and specific ion binding properties which allow a change of its configuration in dependence on shear stress and electrostatic charge density. The blood flow sensor undergoes a conformational transition from a random coil to an extended filamentous state with increasing flow, whereby Na+ ions from the blood are bound. Owing to the intramolecular elastic recoil forces of proteoheparan sulphate the slowing of a flow rate causes an entropic coiling the expulsion of Na+ ions and thus an interruption of the signal chain. Under physiological conditions, the conformation and Na+ binding proved to be extremely Ca2+-sensitive while K+ and Mg2+ ions play a minor role for the susceptibility of the sensor. Via counterion migration of the bound Na+ ions along the sensor glycosaminoglycan side chains and following Na+ passage through an unspecific ion channel in the endothelial cell membrane, the signal transduction chain leads to a membrane depolarization with Ca2+ influx into the cells. This stimulates the EDRF/NO production and release from the endothelial cells. The consequence is vasodilatation.
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| 7. |
- Claesson, PM, et al.
(författare)
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Adsorption and interaction of a graft copolymer of poly(ethylene imine) and poly(ethylene oxide)
- 1996
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 112, s. 131-139
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of proteins and particles onto surfaces carrying firmly adsorbed or covalently bound chains of poly(ethylene oxide) (PEO) is generally very low. This makes it of fundamental and practical interest to learn about the structure of PEO-coatings and how PEO-coated surfaces interact with each other and e.g. proteins. A prerequisite for such studies is, of course, that stable PEO-coated surfaces can be obtained. For this purpose we employed a two-step method to coat negatively charged surfaces, such as mica or silica, with PEO. In the first reaction step, cationic poly(ethylene irnine) is adsorbed onto the negatively charged surface. In the next step, the adsorbed polyelectrolyte is reacted with a functionalized poly(ethylene oxide) chain. Both reaction steps were followed both by ellipsometry and by direct measurement of surface forces. From these measurements we obtained inforrnation of the adsorbed amount, the layer thickness, as well as the range and distance dependence of the interaction between two PEO-coated surfaces.
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| 8. |
- Claesson, Per M, et al.
(författare)
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Surfaces coated with ethyl(hydroxyethyl) cellulose : Temperature effects on adsorption and interaction
- 1995
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Ingår i: Cellulose and Cellulose Derivatives. - : Woodhead Publishing Limited. ; , s. 425-433
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Bokkapitel (refereegranskat)abstract
- The temperature dependence of the forces acting between hydrophobic surfaces coated by a layer of ethyl(hydroxyethyl) cellulose, (EHEC), has been studied as a function of separation and temperature. Both the situation where the adsorbed amount is kept constant and where the adsorbed amount is allowed to vary with temperature have been explored. In both cases the surface interaction is very temperature sensitive due to the temperature dependent interactions between ethylene oxide groups and water. The results are discussed in terms protein repellency of EHEC coated surfaces and in terms of EHEC as a steric stabilizer.
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| 9. |
- Delgado, C, et al.
(författare)
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Analytical partitioning of poly(ethyleneglycol)-modified proteins
- 1997
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Ingår i: Journal of chromatography. B. - 1570-0232 .- 1873-376X. ; 692, s. 263-272
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Tidskriftsartikel (refereegranskat)abstract
- Covalently grafting proteins with varying numbers (n) of poly(ethylene glycol) molecules (PEGs) often enhances their biomedical and industrial usefulness. Partition between the phases in aqueous polymer two-phase systems can be used to rapidly characterize polymer-protein conjugates in a manner related to various enhancements. The logarithm of the partition coefficient (K) approximates linearity over the range 0
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| 10. |
- Griffiths, PC, et al.
(författare)
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Role of copolymer architecture on adsorption at the solid/liquid interface
- 1998
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 14, s. 1779-1785
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of monodisperse block copolymers comprising poly(ethylene oxide)-poly(butylene oxide) onto polystyrene latex from aqueous solution has been investigated by small-angle neutron scattering and photon correlation spectroscopy with particular reference to the role of molecular architecture. It appears that chain architecture is (i) a weak factor in the adsorption behavior when the hydrophobic block is located in the center of the polymer, since the triblock E100B15E100 behaved very similarly to the cyclic c-E200B15, but (ii) a significant factor when the hydrophobic block is located at the end of the copolymer chain, as shown by the more dense and thicker layer formed by E200B15 compared to the triblock E100B15E100. The hydrodynamic thickness of the layer formed by the small diblock E100B15 was approximately half that exhibited by the larger diblock E200B15. Good agreement was observed between depletion and SANS-derived adsorbed amounts. Theoretical predictions and self-consistent mean-field calculations of the adsorption also show excellent qualitative agreement with experiment.
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| 11. |
- Hansen, PHF, et al.
(författare)
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Orthokinetic aggregation in two dimensions of monodisperse and bidisperse colloidal systems
- 1999
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 220, s. 269-280
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Tidskriftsartikel (refereegranskat)abstract
- Orthokinetic aggregation of colloids trapped at the air-liquid interface was studied by direct imaging in a couette cell. This method allowed us to follow the temporal evolution of both the cluster-mass distribution and the cluster structure at a shear rate where Brownian aggregation is suppressed. The interactions between the monodisperse latex particles floating at the air-water interface were controlled either by varying the electrolyte concentration or by creating a bidisperse system through addition of small particles. The results show that the clusters in all the systems are characterized by a high fractal dimension; indicating that the clusters are rearranged and densified by the shear. Kinetic analysis suggests that aggregation of the monodisperse systems mainly proceeds through homogeneous aggregation, i.e. large clusters sticking to other large clusters. The weakly aggregated monodisperse system displayed a transition from heterogeneous to homogenous aggregation of clusters with time which could be related to an incubation time. The bidisperse system, finally, with a size ratio around 10, favored a more heterogeneous aggregation between small and large clusters throughout the aggregation process; a slightly lower fractal dimension was observed compared to the strongly aggregated monodisperse system.
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| 12. |
- Holmberg, K, et al.
(författare)
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Grafting with hydrophilic polymer chains to prepare protein-resistant surfaces
- 1997
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 123-124, s. 297-306
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Tidskriftsartikel (refereegranskat)abstract
- Different ways of grafting poly(ethylene glycol) (PEG) chains to solid polyethylene were compared with respect to grafting density and efficiency in preventing fibrinogen adsorption. Covalent grafting of PEG was performed by attaching a nucleophilic PEG derivative to electrophilic surface groups or by binding electrophilic PEG to nucleophilic groups at the solid surface. Two adsorption procedures were also used. In the first of these an ethylene oxide - propylene oxide (EO-PO) block copolymer was adsorbed at unmodified, hydrophobic polyethylene. In the second procedure the surface was made carboxyl-functional by free radical grafting of tiglic acid and then exposed to a solution of a positively charged copolymer consisting of PEG chains grafted to poly(ethylene imine) (PEI). According to ESCA measurements, all four routes gave proper PEG grafting densities and the difference in the ratio of C–C–O carbon (from PEG) to C-C-C carbon (from the underlying surface) was relatively small. There was a substantial difference in efficiency in fibrinogen rejection, however. Whereas surface modification with the PEG-PEI graft copolymer gave the lowest, treatment with the EO-PO block copolymer gave the highest amount of protein adsorption. The good effect of the PEG-PEI layer is believed to be related to the large entropy loss associated with protein adsorption on top of this copolymer which is known to be loosely bound in a loops-and-trains configuration. The limited effect of the EO-PO block copolymer may be due to the fact that this polymer is not entirely hydrophilic at the temperature used. Another contributing factor may be that the EO-PO block copolymer, unlike the PEG-PEI graft copolymer, is not irreversibly bound to the surface and may therefore be exchanged by fibrinogen.
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| 13. |
- Lassen, Bo, et al.
(författare)
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Competitive protein adsorption at plasma polymer surfaces
- 1997
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 186, s. 9-16
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Tidskriftsartikel (refereegranskat)abstract
- Competetive adsorption from a ternary mixture of human serum albumin (HSA), human IgG, and human fibrinogen (FGN) at concentrations corresponding to blood plasma diluted 1/100 was investigated with the combination of Total Internal Reflection Fluorescence spectroscopy (TIRF) and ellipsometry. As substrates, three different plasma polymer surfaces, representing different surface charge and surface energy, were prepared from hexamethyldisiloxane (PP-HMDSO), acrylic acid (PP-AA), and 1,2-diaminocyclohexane (PP-DACH). In addition, adsorption from single and binary protein systems was investigated with ellipsometry. At the hydrophobic PP-HMDSO little or no displacement of any of the proteins was observed. The adsorbed layer was dominated by HSA and IgG, although Fgn was also present to a smaller extent. On PP-DACH and PP-AA, representing positively and negatively charged hydrophilic surfaces, respectively, Fgn completely dominated the adsorbed layer while HSA was almost absent and IgG was present only at a very low level.
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| 14. |
- Lassen, Bo, et al.
(författare)
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Competitive protein adsorption studied with TIRF and ellipsometry
- 1996
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 179, s. 470-477
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Tidskriftsartikel (refereegranskat)abstract
- Total internal reflection fluorescence (TIRF) and ellipsometry have been used to study competitive protein adsorption to a hydrophobic model surface prepared by radio frequency plasma deposition of hexamethyl disiloxane on silicon. Single, binary, and ternary protein solutions of human serum albumin (HSA), IgG, and fibrogen (Fgn) at concentrations corresponding to 1/100 of those in blood plasma were investigated. It is shown that by employing the combination of ellipsometry and TIRF, information on both the total adsorbed amount and the composition of the adsorbed protein layer can be obtained. It was found that adsorbed HSA is not displaced by IgG and/or Fgn to any large extent. IgG and HSA dominate the adsorption from the ternary protein mixture, although fibrinogen is also present in the adsorbed layer to a smaller extent.
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| 15. |
- Lassen, Bo, et al.
(författare)
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Structure of protein layers during competitive adsorption
- 1996
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 180, s. 339-349
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Tidskriftsartikel (refereegranskat)abstract
- The formation of protein layers during competitive adsorption was studied with ellipsometry. Single, binary, and ternary protein solutions of human serum albumin (HSA), IgG, and fibrinogen (Fgn) were investigated at concerntrations corresponding to blood plasma diluted 1/100. As a model surface, hydrophobic hexamethyldisiloxane (HMDSO) plasma polymer modified silica was used. By using multiambient media measurements of the bare substrate prior to protein adsorption the adsorbed amount as well as the thickness and refractive index of the adsorbed protein layer could be followed in situ and in real time. Under conditions used in these experiments neither IgG nor fibrinogen could fullydisplace serum albumin from the interface. The buildup of the protein layer occured via different mechanisms for the different protein systems. Fgn adsorbed in a rather flat orientation at low adsorbed amounts, while at higher surface coverage the protein reoriented to a more upright orientation in order to accommodate more molecules in the adsorbed layer. IgG adsorption proceeded mainly end on with little reorientation or conformational change on adsorption. Finally, for HSA an adsorbed layer thickness greater than the molecular dimensions was observed at high concentrations ( although not at low ), indicating that aggregates or multilayers formed on HMDSO plasma polymer surfaces. For all protein mixtures the adsorbed layer structure and buildup indicated that Fgn was the protein dominating the adsorbed layer, although HSA partially blocked the adsorption of this protein. At high surface concentration, HSA/Fgn mixtures show an abrupt change in both adsorbed layer thickness and refractive index suggesting, e.g., an interfacial phase transition of the mixed protein layer. A similar but less pronounced behavior was observed for HSA/IgG. For IgG/Fgn and HSA/Fgn a buildup of the adsorbed layer similar to that displayed by Fgn alone was observed.
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| 16. |
- Lee, L-T, et al.
(författare)
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Lipase-surfactant interactions studied by neutron reflectivity and ellipsometry
- 1999
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Ingår i: Journal of Physical Chemistry B. - 1520-6106 .- 1520-5207. ; 103, s. 7489-7494
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between a microbial lipase and an anionic and a cationic surfactant at the air-water interface has been studied by neutron reflectivity. Sodium dodecyl sulfate (SDS) and tetradecyltrimethylammonium bromide (TTAB) were used as anionic and cationic surfactant, respectively. The same enzyme-surfactant systems were also studied at the interface between a hydrophobic solid surface and water by ellipsometry, and the results from the two techniques were compared. Surface tension measurements were also performed in order to monitor complex formation in bulk. The data obtained from neutron reflectivity and from ellipsometry were in very good agreement with each other. Both techniques show that lipase adsorbs readily at the interfaces and that SDS at low concentration does not interact strongly with this protein layer. At higher SDS concentration, the protein is displaced from the surface. On the other hand, when TTAB is added at low concentration, a thick lipase-surfactant layer is formed at the surfaces. This compact layer is solubilized by further addition of the cationic surfactant.
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| 17. |
- Lindström, A, et al.
(författare)
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Interactions in phospholipid stabilized emulsion system
- 1999
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Ingår i: Journal of Dispersion Science and Technology. - 0193-2691 .- 1532-2351. ; 20, s. 247-256
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between a phospholipid stabilized triglyceride emulsion and a hydrophilic silica surface has been studied at varying pH and electrolyte content using ellipsometry. The adsorbed amount decreases with pH and increases with increasing electrolyte content in the emulsion, and this can be rationalized on the basis of the electrostatic interaction between the emulsion droplet and the surface. The layer thickness, however, is essentially independent of these parameters. In addition, the emulsion has been studied during turbulent shear conditions (applied mechanical stress), with the same variation of pH and electrolyte as in the adsorption experiments. A decrease in pH and an increase in electrolyte content, decreasing the repulsive interaction between the droplets, leads to a deterioration in emulsion stability with time.
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| 18. |
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| 19. |
- Malmsten, M, et al.
(författare)
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Adsorption of complement protein C3 at polymer surfaces
- 1996
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 179, s. 163-172
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of C3 at poly(methyl methacrylate) (PMMA) and poly(styrene) (PS) surfaces was investigated with in situ ellipsometry and compared to that at (hydrophilic and negatively charged) silica and (hydrophobic) methylated silica. The adsorption of C3 at PMMA was higher than that at PS, while the adsorbed layer thickness was the same for the two surfaces. For both PMMA and PS the adsorbed layer thickness (10±2 nm) corresponds rather closely to that of end-on oriented C3 molecules. The adsorption of C3 at PMMA and PS was found to be intermediate between that at silica and methylated silica, although the adsorbed layer thickness was similar for all surfaces. The competitive adsorption between C3, human serum albumin (HSA), and factor B was investigated with ellipsometry and total internal reflection fluorescence spectroscopy (TIRF). Addition of HSA after C3 preadsorption resulted in fractional C3 desorption for both PMMA and PS. Factor B deposition at PS after preadsorption of C3 and blocking with HSA was found to be largely due to specific binding to C3/C3b, while in the case of PMMA, factor B was largely accumulated through passive (displacement) adsorption.
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| 20. |
- Malmsten, M, et al.
(författare)
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Adsorption of complement proteins C3 and C1q
- 1996
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 178, s. 123-134
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Tidskriftsartikel (refereegranskat)abstract
- Surface localization plays a key but ill defined role in activation of the Serum Complement System with or without related "opsonic" proteins. The adsorption of key complement components C3 and C1q and various opsonins, e. g., IgG, were therefore studied on different surfaces using in situ ellipsometry. The affinities of C3 and C1q for silica, methylated silica, and various phospholipid surfaces were shown to be largely reciprocal. While C3 adsorbed more extensively at (hydrophilic and negatively charged) silica than at (hydrophobic) methylated silica (3.1 versus 0.4 mg/m2, respectively) the opposite trend was observed for C1q (1.9 versus 2.6 mg/m2). C3 and C1q adsorbed in 10 to 15 nm thick layers on both silica and methylated silica. Each protein appeared to adsorb with consistent conformation and orientation on either surface. Adsorbed layer formation involves increased protein packing density, and molecular extension normal to the surface. Phospholipid head group properties strongly affect the adsorption of C3 and C1q at phospholipid coated surfaces. The saturation adsorption of C3 at phosphatidic acid was almost as significant as at silica, whereas the amount adsorbed at phosphatidylcholine was three times lower. C3 adsorption at phosphatidylinositol and various poly(ethylene glycol) modified surfaces was virtually absent, as was the adsorption of various opsonins. C1q adsorption was relatively low at all phospholipid and poly(ethylene glycol) coated surfaces investigated, more in the manner of IgG than C3. Preadsorption of IgG increased C1q deposition at phospholipid surfaces strongly. C3 and human serum albumin, but not C1q, showed appreciable hydrophobic affinity for a poly(ethylene glycol)-fatty acid ester of oleic acid. These results are discussed in relation to complement interaction with various surfaces and colloidal drug carriers.
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| 21. |
- Malmsten, M, et al.
(författare)
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Adsorption of poly(ethylene glycol) amphiphiles to form coatings which inhibit protein adsorption
- 1996
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 177, s. 502-512
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of poly(ethylene glycol) (PEG)-esterified fatty acids at methylated silica, phosphatidic acid and phosphatidylcholine surfaces was investigated with in situ ellipsometry. For a series of PEG-fatty acid esters of ethoxy groups and acyl tails of the type Ci:j-EO151 (16≤i≤18, 0≤j≤2) adsorption at methylated silica was independent of bulk micellization, and plateau was reached below the critical micellization concentration (CMC). The plateau adsorbed amount for the investigated fatty acid esters was only weakly dependent on the nature of the hydrophobic moiety. Instead, saturation adsorption was largely determined by the interactions between PEG chains. Adsorption isotherms were therfore essentially identical on all three of the quite different surfaces. At saturation adsorption, the adsorbed layer thickness was 10-15 nm, while the average adsorbed layer concentration was 0.07 g/cm3. Formation of the PEG-surfactant coatings thus appeared to involve significant molecular alterations of PEG from a random coil. The ability of the PEG-ester coatings to inhibit protein adsorption was also investigated. At adsorption plateau, all coatings investigated displayed quite good ability to inhibit adsorption by a number of serum proteins. For all three surfaces studied this ability decreased below 0.2·CMC. These findings are discussed in relation to the ability of PEG-derivatized lipids to control the in vivo fate of colloidal drug carriers.
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| 22. |
- Malmsten, M, et al.
(författare)
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Competitive protein adsorption at phospholipid surfaces
- 1995
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Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 4, s. 173-184
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Tidskriftsartikel (refereegranskat)abstract
- The interfacial exchange processes between human serum albumin (HSA) and fibrinogen at different surfaces was investigated with in situ ellipsometry and TIRF. With ellipsometry, it was found that the total adsorbed amount at silica on addition of fibrinogen after preadsorption of HSA was quite similar to that obtained without HSA preadsorption. From TIRF, it is concluded that the preadsorbed HSA is displaced, although not completely, on addition of fibrinogen. On the other hand, preadsorbed HSA effectively blocked further adsorption of fibrinogen and IgG at hydrophobic surfaces such as methylated silica. Furthermore, the competitive adsorption of HSA and fibrinogen at two phospholipid surfaces, i e, phosphatidylcholine (PC) and phosphatidic acid (PA), was investigated. It was found that at PA, fibrinogen adsorbs extensively even after preadsorption of HSA. This, however, is achieved with essentially no displacement of the preadsorbed HSA. For PC, finally, the fibrinogen adsorption is much lower than that of HSA, and fibrinogen is able neither to coadsorb with HSA nor to displace the preadsorbed protein.
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| 23. |
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| 24. |
- Malmsten, M, et al.
(författare)
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Effect of chain density on inhibition of protein adsorption by poly(ethylene glycol) based coatings
- 1998
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 202, s. 507-517
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Tidskriftsartikel (refereegranskat)abstract
- The effect of interfacial chain density of poly( ethylene glycol) (PEG) on the adsorption of serum proteins was investigated by in situ ellipsometry. For terminal covalently grafted PEG of molecular weight 5000 an increased grafting density results in serum protein adsorption. At high interfacial chain density ( É 0.1 chain/nm2) , efficient protein rejection was observed, irrespective of the coupling chemistry used. Strongly adsorbed PEG-containing polymers behaved similarly to covalently attached PEG regarding inhibition of protein adsorption, independent of the nature of the underlying surface. The results are discussed in relation to the importance of the protein size in protein rejection by PEG coatings.
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| 25. |
- Malmsten, M, et al.
(författare)
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Effects of amino acid composition on protein adsorption
- 1996
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 178, s. 160-167
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption at silica and methylated silica of genetically engineered derivatives of Z and its dimer ZZ, where Z is a hydrophilic synthetic IgG binding domain derived from staphylococcal protein A, was studied with in situ ellipsometry. The protein modifications consisted of introducing short peptide stretches near the C-terminus of the protein. Using this approach, oligopeptide stretches containing hydrophobic tryptophan (Trp) or isoleucine (Ile) [(AlaTrpTrpPro)n or (AlaIleIlePro)n (0≤n≤2), denoted Tn and In, respectively] were introduced in the protein. For comparison, the adsorption of the inserted peptide stretches (Tn and In), as well as of Trp and Ile oligomers, was investigated as well. Increasing the number of Trp residues resulted in an increased adsorption for both ZZTn, ZTn, Tn, and Trpn. At a given number of Trp residues, the adsorbed amount of the ZZ derivatives is larger than that of the peptides, but about the same as that of the Z proteins. Analogous although somewhat smaller effects were obtained for the Ile-derivatized proteins. These results are discussed in terms of the "block copolymer" nature of the proteins. Theoretical calculations using a mean-field lattice model for block copolymer adsorption gave a qualitative agreement with the experimentally obtained results.
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| 26. |
- Malmsten, M, et al.
(författare)
-
Effects of hydrophilization and immobilization on the interfacial behaviour of immunoglobulins
- 1996
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 177, s. 70-78
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption and immobilization of rabbit anti-human immunoglobulin (rabbit IgG), as well as the effects on the amount and reactivity of bound rabbit IgG of rinsing with buffer and addition of bovine serum albumin (BSA) or human IgG, were investigated with ellipsometry, TIRF and enzyme immuno assay (EIA). It was found that although rabbit IgG readily adsorbs at hydrophobic hexamethyldisiloxane (HMDSO) plasma polymer surfaces, a substantial fraction of the adsorbed protein molecules are desorbed on rinsing with buffer. BSA was found to adsorb readily at the surfaces obtained after rinsing, although also this protein desorbed to a large extent on further rinsing with buffer. The adsorption of BSA causes a further reduction in the amount of rabbit IgG adsorbed. Immobilization of rabbit IgG to acrylic acid (AA) plasma polymer surfaces, achieved by covalent coupling via a strongly adsorbed PEG-PEI copolymer, was found to overcome the problem of desorption of rabbit IgG on rinsing with buffer or addition of BSA. Furthermore, non-specific adsorption was virtually absent after immobilization. However, covalently bound rabbit IgG reacted strongly with human IgG, as observed by ellipsometry, TIRF and EIA. The immobilization of rabbit IgG to hydrophilized surfaces was found to facilitate the interpretation of EIA results.
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| 27. |
- Malmsten, M, et al.
(författare)
-
Electrostatic and hydrophobic effects of oligopeptide insertions on protein adsorption
- 1998
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 204, s. 104-111
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of oligopeptide insertions on the adsorption of the protein ZZ, where Z is the IgG binding domain of staphylococcal Protein A, was investigated by in situ ellipsometry. In particular, the interplay between hydrophobic and electrostatic interactions as driving force for adsorption was investigated by studying the effects of oligopeptide insertions of the type Tn(AlaTrpTrpPro), Na ((AlaTrpTrpLysPro)n), and Pn((AlaTrpTrpLysPro)n) on the adsorption at silica, methylated silica , and diaminocyclohexane (DACH) plasma polymer surfaces. For comparison, the adsorption of the inserted peptide stretches was also investigated. It was found that the adsorption of all the peptides increases with the molecular weight at methylated silica. At silica, only the Pn peptides were found to adsorb. The net negatively charged proteins modified through peptide insertions did not adsorb at the hydrophilic and negatively charged silica, irrespective of the peptide insertion, whereas an extensive adsorption was found for the posetively charged DACH surface for all the proteins investigated. For hydrophobic and negatively charged methylated silica, on the other hand, the peptide insertions were found to have a major influence on the protein interfacial behavior, and the adsorption followed the peptide stretch charge, thus increasing in the order ZZNn< ZZTn < ZZPn. These effects are discussed in terms of the relative importance of hydrophobic and electrostatic interactions as driving force for the adsorption.
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| 28. |
- Malmsten, M, et al.
(författare)
-
Electrostatic and ion-binding effects on the adsorption of proteoglycans
- 1995
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 170, s. 120-127
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of proteoheparan sulphate, a strongly negatively charged proteoglycan, at (hydrophobic) methylated silica surfaces was investigated with in situ ellipsometry. In particular, the effects of electrolytes in the physiological concentration ranges were studied. Both general electrostatic and cation-specific ion-binding effects were shown to be important for the interfacial behaviour of this macromolecule. While Ca2+ causes an increase in the adsorbed amount of proteoheparan sulphate at hydrophobic surfaces at physiological conditions, the effects of Mg2+ were the reverse, and of a much smaller magnitude. Similar finding were obtained for proteodermatan/-chondroitin sulphate, as well as for the heparan sulphate side-chains of proteoheparan sulphate. Furthermore, both Na+ and K+ cause an increase in the adsorption in certain concentration ranges, due to electrostatic reasons. However, Na+ and K+ were also found to oppose the effects of Ca2+. Moreover, the effects of K+ are of a smaller magnitude than those of Na+ and occur over a longer time-scale. Thus, general electrostatic effects, as well as cation-specific ion-binding effects are of importance for the biological performance of proteoglycans, e g, in the endothelial cell membrane.
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| 29. |
- Malmsten, M, et al.
(författare)
-
Electrostatic effects on interfacial film formation in emulsion systems
- 1996
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 179, s. 537-543
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption at silica from dilute emulsion systems was studied with in situ ellipsometry. In particular, the effects of electrostatic interactions on the adsorption rate and the adsorbed layer structure and formation was investigated by varying the emulsion droplet and surface charge, as well as the electrostatic screening, accomplished by varying pH and the excess electrolyte concentration. Electrostatic interactions were found to markedly affect the adsorption rate, but not the adsorbed layer structure or the mechanism for the adsorbed layer formation. For all cases investigated, the adsorbed layer thickness corresponds to emulsion droplets or multilamellar liposomes, and the adsorbed layer formation proceeds through attachment of emulsion droplets and/or multilamellar liposomes at the surface without extensive droplet spreading or liposome collapse. When the droplets and the surface are similarly charged, the adsorption is facilitated by increasing the electrostatic screening or by decreasing the emulsion droplet and surface charge, accomplished by increasing the excess electrolyte concentration and decreasing pH, respectively. When the droplets and the surface are oppositely charged, the adsorption rate is much higher than that observed when the droplets and the surface are similarly charged, although the adsorbed layer structure and the mechanism for the adsorbed layer formation are similar. Qualitatively, these effects may be understood by considering only electrostatic and van der Waals interactions.
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| 30. |
- Malmsten, M
(författare)
-
Ellipsometry and TIRF studies of adsorption processes in parenteral drug delivery
- 1997
-
Ingår i: Interface science. - 0927-7056 .- 1573-2746. ; 5, s. 159-167
-
Tidskriftsartikel (refereegranskat)abstract
- Ellipsometry and total internal reflection fluorescence spectroscopy (TIRF) were used for investigating adsorption processes of relevance for parenteral administration of colloidal drug carriers. Emphasis is put on discussing the effects of both protein and surface properties on the adsorption of serum proteins at phospholipid and other surfaces. Furthermore, the adsorption from multicomponent protein systems, such as blood, is addressed, and both competitive and associative adsorption phenomena discussed. The correlation between effects of the drug carrier surface properties on the serum protein adsorption and the circulation time and tissue distribution of colloidal drug carriers is also addressed. Finally, the potential of ellipsometry in another adsorption process of major importance for phagocytosis, i.e., the adsorption of colloidal particles to macroscopic or mesoscopic surfaces, is indicated by investigations of the adsorption of oil-in-water emulsion droplets at silica.
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| 31. |
- Malmsten, M
(författare)
-
Ellipsometry studies of fibronectin adsorption
- 1995
-
Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 3, s. 371-381
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of fibronectin at a series of different surfaces was investigated with in situ ellipsometry. For silica and methylated silica, the adsorbed amount (G), the adsorbed layer thickness (del) and the mean adsorbed layer refractive index (nf) were obtained by a procedure involving studies of the bare substrate at two different ambient refractive indices, as well as four-zone averaging. It was found that the adsorbed amount of fibronectin was the same (1.9±0.1 mg/m2) at silica and methylated silica. However, the adsorbed layers formed at methylated silica were more extended and had a lower average protein concentration than those formed at silica. Furthermore, at both silica and methylated silica, an increasing adsorbed amount is achieved both by a denser packing of the fibronectin molecules and by a growth of the adsorbed layer normal to the surface. Furthermore, the adsorption of fibronectin at lipid surfaces was investigated. It was found that the adsorption of fibronectin to phosphatidic acid was quite significant (2.2±0.2 mg/m2), while that at phosphatidylcholine, phosphatidylinositol and phosphatidylserine was much smaller (all 0.1±0.05 mg/m2). These results are correlated to findings on the adsorption of fibrinogen at these surface, as well as on the opsonization of lipid-stabilized colloidal particles.
|
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| 32. |
- Malmsten, M, et al.
(författare)
-
Ellipsometry studies of interfacial film formation in emulsion systems
- 1995
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 173, s. 297-303
-
Tidskriftsartikel (refereegranskat)abstract
- The possibility of using in situ ellipsometry for studies of the formation of interfacial films in emulsion systems was investigated. It was found that ellipsometry studies on dilute emulsion can provide information on both the adsorption kinetics, the adsorbed layer structure and the mechanisms for the adsorbed layer formation. At high electrolyte concentrations, the adsorption from a model o/w emulsion stabilized by egg lecithin was found to be more pronounced at hydrophilic and negatively charged silica than at hydrophobic methylated silica. Furthermore, the adsorbed layer thickness at both surfaces is smaller than the average droplet size, corresponding to either small or ”flattened” droplets or liposomes. The adsorbed layer thickness is smaller at methylated silica than at silica, presumably due to a larger degree of emulsion droplet or liposome spreading at this surface. In both cases, the adsorbed layer thickness is independent of the adsorbed amount, i. e. the adsorbed layer formation proceeds by attachment of droplets, which pack more densly with an increasing adsorbed amount.
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| 33. |
- Malmsten, M
(författare)
-
Ellipsometry studies of the effect of surface hydrophobicity on protein adsorption
- 1995
-
Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 3, s. 297-308
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of some model proteins, human serum albumin (HSA), IgG, fibrinogen and lysozyme at silica surfaces was investigated with in situ ellipsometry and compared to previous results obtained for methylated silica surfaces. The adsorbed amount (G), the adsorbed layer thickness (del) and the mean adsorbed layer refractive index (nf) were obtained by a procedure involving studies of the bare substrate at two different ambient refractive indices, as well as four-zone averaging. The surface hydrophobicity strongly influenced the adsorption properties of all the proteins studied. For HSA, IgG and fibrinogen, the adsorbed amount was significantly lower at the hydrophilic surface than at the hydrophobic one, whereas the reverse was found for lysozyme. For fibrinogen, the adsorbed layer thickness at silica was smaller than that at methylated silica, whereas the adsorbed layer was more concentrated. For IgG, on the other hand, end-on adsorption was observed at both silica and methylated silica. For lysozyme, side-on adsorption in a dense monolayer was observed at silica, whereas at methylated silica, the adsorption occurs in 2-3 rather dilute molecular layers. Furthermore, the build-up of the adsorbed layers was studied. For fibrinogen, qualitatively the same behaviour was observed for silica and methylated silica, i e, as the adsorbed amount increases, both del and nf increase initially, while closer to adsorption saturation, nf levels off. However, at a given G, del was lower and nf higher at silica than at methylated silica. A similar finding was obtained for lysozyme. These findings are discussed in terms of the adsorbed layer structure and formation.
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| 34. |
|
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| 35. |
- Malmsten, M, et al.
(författare)
-
Interfacial behaviour of 'new' poly(ethylene oxide)-containing copolymers
- 1999
-
Ingår i: Journal of Biomaterials Science. Polymer Edition. - 0920-5063 .- 1568-5624. ; 10, s. 1075-1087
-
Tidskriftsartikel (refereegranskat)abstract
- Block copolymers containing poly(ethylene oxide) (PEO) have a wide applicability within biomedical applications, not the least due to anti-fouling properties of surface coatings based on these copolymers. We have investigated a number of these, and results for PEO/poly(butylene oxide) (PEO/PBO), PEO/poly(lactide) (PEO/PL), and PEO/poly(ethylene imine) (PEO/PEI) copolymers, as well as for PEO-esterified fatty acids, are presented and discussed. For the former class of polymers, the effects of molecular architecture on the adsorption properties are adressed, and experimental results obtained with ellipsometry and small-angle neutron scattering presented. For the PEO/PL block copolymers, the effects of the PEO and PL lengths for the polymer adsorption are adressed, as are the effects of degradation of the PL moiety on both adsorption and protein rejection. For the PEO-esterified fatty acids, the effects of PEO chain length and interfacial density on the protein rejection capacity of such coatings are discussed.
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| 36. |
- Malmsten, M, et al.
(författare)
-
Protein adsorption at n-butane plasma polymer surfaces
- 1996
-
Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 6, s. 191-199
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of human serum albumin (HSA) and fibrinogen at n-butane plasma polymer surfaces prepared by low temperature plasma polymerization at different energy inputs have been investigated with in situ ellipsometry. Within experimental uncertainty, the adsorption of both fibrinogen and HSA is constant over the power range used for the preparation of the n-butane surfaces and corresponds to that found for other hydrophobic surfaces at similar conditions. Furthermore, novel copolymer surfaces of n-butane and nitrogen at different ratios were prepared and investigated. Increasing the nitrogen content in the gas mixture during deposition resulted in an increased density of interfacial amine groups, as evidenced by an increased wettability, an increased interfacial nitrogen content, and an increased surface positive charge. This, in turn, was found to result in an increased fibrinogen adsorption, but in a weak decrease in the HSA adsorption.
|
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| 37. |
- Malmsten, M
(författare)
-
Protein adsorption at phospholipid surfaces
- 1995
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 172, s. 106-115
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of human serum albumin (HSA), IgG, fibronectin and fibrinogen at phospholipid surfaces was studied with in situ ellipsometry. For comparison, a model hydrophobic surface (methylated silica) and a model hydrophilic surface (silica) were also included in the study, as was a surface coated with an ethylene oxide/propylene oxide (EO/PO) block copolymer. The phospholipid head group composition was found to have a major effect on the serum protein adsorption. Surfaces with either no net charge or shielded charges, e. g. phosphatidylcholine (PC), phosphatidylethanolamine (PE), sphingomyelin (SM) and phosphatidylinositol (PI) or ganglioside GM1, generally give a low adsorption of serum proteins of importance for opsonization, in analogy to the performance of adsorbed water-soluble polymers (e. g. EO/PO block copolymers), while those containing either unprotected charges, e. g. phosphatidic acid (PA), diphosphatidylglycerol (DPG), phosphatidylserine (PS) and silica, or hydrophobic domains (methylated silica), result in a high opsonin protein adsorption. However, the effects studied are complex, and different serum proteins generally behave quite differently at a given surface.
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| 38. |
- Malmsten, M, et al.
(författare)
-
Sequential adsorption of human serum albumin (HSA), immunoglobulin G (IgG), and fibrinogen (Fgn) at HMDSO plasma polymer surfaces
- 1997
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 193, s. 88-95
-
Tidskriftsartikel (refereegranskat)abstract
- The sequential adsorption of human serum albumin (HSA), immunoglobulin G (IgG), and fibrinogen (Fgn) at hexamethyldisiloxane (HMDSO) plasma polymer surfaces was investigated with ellipsometry and total internal reflectance fluorescence spectroscopy (TIRF) as a function of adsorption time, pH, and excess electrolyte concentration. HSA was found to self-exchange very slowly (≈hours) at pH 7.2, irrespective of adsorption time in the range 90 seconds to 90 minutes. Preadsorbed HSA was exchanged by Fgn and IgG only to a limited extent irrespectively of pH (5≤pH≤8) and excess electrolyte concentration (5 mM≤Cs≤150 mM). At an excess electrolyte concentration of 150 mM, the sequential adsorption of Fgn and IgG was dramatically reduced by HSA preadsorption, irrespective of pH. At an excess electrolyte concentration of 5 mM, on the other hand, there were indications of second layer adsorption of Fgn and IgG.
|
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| 39. |
- Malmsten, M
(författare)
-
Studies of serum protein adsorption at phospholipid surfaces in relation to intravenous drug delivery
- 1999
-
Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 159, s. 77-87
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of serum proteins at phospholipid surfaces was investigated in relation to uptake of intravenously administered colloidal drug carriers. In particular, an approach based on the use of surface-modified flat substrates for investigations of the adsorption pattern by in situ ellipsometry and surface plasmon resonance is discussed. Similar results regarding protein adsorption were obtained for phosphiolipid layers prepared through spin-coating, Langmuir-Blodgett deposition, and liposome adsorption. Furthermore, a good agreement was found between the adsorption at the model surfaces, on one hand, and at oil-in-water emulsion droplets, on the other, suggesting that curvature effects on the adsorption are minor. By the use of this approach, the adsorption of a number of proteins at a range of surfaces was investigated. Also mixed (phospho)lipid layers were studied, as was the adsorption from diluted serum and plasma. The results obtained are discussed in relation to the effects of the surface properties on the performance of colloidal drug carriers.
|
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| 40. |
- Millqvist-Fureby, Anna, et al.
(författare)
-
Spray-drying of trypsin – Surface characterisation and activity preservation
- 1999
-
Ingår i: International Journal of Pharmaceutics. - 0378-5173 .- 1873-3476. ; 188, s. 243-253
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study trypsin mixed with various carbohydrates, i.e. lactose, sucrose, mannitol, a-cyclodextrin and dextrin, was spray-dried in order to investigate the effects of spray-drying on this enzyme, with particular emphasis on the effects of interactions between trypsin and the surface formed during spray-drying. The protein was strongly over-represented at the surface of the powder particles, the surface coverage ranging from 10 to 65%, depending on the amount of trypsin in the solids (0.2-5%). This indicates that the protein adsorbs at the air/liquid interface of the spray-droplets, and that this surface is largely preserved also after drying. The surface concentration of protein in the spray-dried powders could be controlled by adding a surfactant to the mixture before drying, since the surfactant adsorbs preferentially at the air/liquid interface of the spray droplets, thus expelling protein from the surface. In general, the residual activity of trypsin in these non-optimised formulations was 90% or higher, and in no case less than 82%. It was found that the loss of activity could partly be explained by inactivation of the protein adsorbed at the surface. For mannitol and sucrose, however, the level of inactivation was higher than could be explained by surface inactivation alone, and additional mechanisms must also be considered.
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| 41. |
- Millqvist-Fureby, Anna, et al.
(författare)
-
Surface characterisation of freeze-dried protein/carbohydrate mixtures
- 1999
-
Ingår i: International Journal of Pharmaceutics. - 0378-5173 .- 1873-3476. ; 191, s. 103-114
-
Tidskriftsartikel (refereegranskat)abstract
- In the present investigation freeze-drying of proteins (BSA or trypsin) together with various carbohydrates, i.e. lactose, sucrose, mannitol, a-cyclodextrin and dextrin, has been studied with particular emphasis on the surface composition of the freeze-dried powders. The proteins were found to be over-represented on the powder surface as compared to the bulk concentration of protein. The mechanism behind the surface accumulation is believed to be that proteins adsorb preferentially over carbohydrates to the ice/liquid interface in the frozen sample. The degree of surface accumulation depended on the carbohydrate used, and was increased in annealed samples compared to reference samples. The activity of trypsin was fairly preserved well (58-90%) in the freeze-dried powders, but depended on the carbohydrate excipient, whilst the surface composition had little effect on the activity. The activity preservation was improved when the protein concentration was raised from 1% to 10% in the solids. The surface composition of powders containing mixtures of mannitol and dextrin as excipients depended on the ratio between the two carbohydrates, with the lowest surface coverage of protein obtained in 50/50 mixtures.
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| 42. |
- Muller, D, et al.
(författare)
-
Competitive adsorption of gelatin and sodium dodecylbenzenesulfonate at hydrophobic surfaces
- 1998
-
Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 14, s. 3107-3114
-
Tidskriftsartikel (refereegranskat)abstract
- The competitive adsorption of gelatin and sodium dodecylbenzenesulfonate (SDBS) at hydrophobic surfaces was investigated with surface and interfacial tension measurements, ellipsometry, surface plasmon resonance spectroscopy (SPR), and total internal reflectance fluorescence spectroscopy (TIRF). From both ellipsometry and SPR, initial additions of SDBS after gelatin preadsorption were found to result in a total adsorbed amount increase, as well as in a swelling of the adsorbed layer. At higher SDBS concentrations, both the total adsorbed amount and the amount of gelatin adsorbed decrease, which was observed from ellipsometry, SPR, and TIRF. From surface and interfacial tension measurements, it was found that the critical aggregation concentration (cac) for the SDBS-gelatin system decreases with decreasing pH. Analogous to this, ellipsometry, SPR, and TIRF indicate that the SDBS concentration required to cause a significant decrease in the gelatin adsorbed amount decreases with decreasing pH. The desorption therefore seems to be correlated to the SDBS binding to the adsorbed gelatin molecules rather than to purely competitive adsorption.
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| 43. |
- Muller, D, et al.
(författare)
-
Interaction of gelatin and sodium dodecyl benzene sulphonate at oil and water interfaces
- 1997
-
Ingår i: Imaging Science Journal. - 1368-2199 .- 1743-131X. ; 45, s. 229-235
-
Tidskriftsartikel (refereegranskat)abstract
- Interaction between sodium dodecyl benzene sulphonate (SDBS) and gelatin was studied in relation to emulsification behaviour and emulsion stability. We chose two different oils to study influences of oil phase characteristics, namely, tricresyl phosphate (TCP) as an oil with polar and slightly hydrophilic nature, and n-docedane (nC12) as its apolar contrast. Our interfacial tension measurements showed that both TCP and n-C12 give critical values (i.e., cac and cmc) very close to those of surface tension measurement. This result indicates that the complexation behaviour in bulk solution is independent of the presence or the nature of the oil phase. Absolute tension values above the cmc and slope values at the cmc in gelatin free systems, however, imply SDBC's weaker adsorption to TCP than to n-C12. Our emulsification results for the TCP system revealed the existence of an optiomal point for emulsion stability in the SDBS concentration region between the cac and the cmc. Above this point, emulsion stability deteriorates remarkably. The behaviour is in line with our findings from the dynamic sorption expriments (ellipsometry, TIRF, and SPR) reported elsewhere, which showed a rapid desorption of gelatin from the hydrophobic surfaces above the cac. The results suggest that the adsorption of gelatin/ surfactant complexes at the interface is a key factor for stability of the polar oil emulsion system. Contrary to that , the n-c12 system did not show any deterioration, even above the cmc, which is presumably due to a strong double layer effect from the firmly adsorbed layer of SDBS at the interface.
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| 44. |
- Siegel, G, et al.
(författare)
-
Flow sensing at the endothelium-blood interface
- 1998
-
Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 138, s. 345-351
-
Tidskriftsartikel (refereegranskat)abstract
- Viscoelastic and polyelectrolytic heparan sulfate proteoglycan (syndecan) integrated into the membrane of vascular endothelial cells may serve as a flow sensor.This biosensor macromolecule responds to shear stress by a conformational change. Cations function as a first messenger in the signal transduction chain for a dilatory vessel reaction with increasing blood flow. Application of 23Na + NMR techniques proved useful in the characterization of shear stress-dependent conformational changes and reversible Na+ binding of proteoheparan sulfate, a strongly negatively charged proteoglycan. Ca2+ ions interfere with Na+ uptake and release in a competitive or cooperative manner. The adsorption of heparan sulfate proteoglycan at hydrophobic silica surfaces, as measured by in situ ellipsometry, was shown to be dependent on both general electrostatic and cation-specific ion binding actions. The interfacial behaviour of this macromolecule is characterized by an increase in the adsorbed amount upon addition of Ca2+, while Mg2+ induces the opposite effect of much smaller magnitude.
|
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| 45. |
- Siegel, G, et al.
(författare)
-
Physicochemical binding properties of the proteoglycan receptor for serum lipoproteins
- 1999
-
Ingår i: Atherosclerosis. - 0021-9150 .- 1879-1484. ; 144, s. 59-67
-
Tidskriftsartikel (refereegranskat)abstract
- Proteoheparan sulfate can be adsorbed to a methylated silica surface in a monomolecular layer via its transmembrane hydrophobic protein core domain. Due to electrostatic repulsion, its anionic polysugar side chains are stretched out into the blood substitute solution representing a co-receptor for specific lipoprotein binding through basic amino acid-rich residues within their apolipoproteins. The binding process was studied by ellipsometric techniques showing that oxLDL had a deleterious effect on heparan sulfate proteoglycan binding and conformation. Ca2+ binding to and storage on the proteoheparan sulfate/LDL compound formed a 'heterotrimeric' HS-PG/LDL/Ca2+ complex of high stability, aggregability and deposit coating. On the other hand, HDL bound to heparan sulfate proteoglycan protected against LDL docking and completely suppressed calcification of the proteoglycan/lipoprotein complex.
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| 46. |
|
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| 47. |
- Siegel, G, et al.
(författare)
-
The role of the endothelium in inflammation and tumor metastasis
- 1997
-
Ingår i: Int J Microcirc. - 0167-6865. ; 17, s. 257-272
-
Tidskriftsartikel (refereegranskat)abstract
- In inflammation, cells interact with extracellular matrices or neighboring cells by a spatiotemporal intervention pattern of specific cell surface receptors and adhesion molecules. Resident cells of the injured tissue communicate with circulating effector cells by cytokines and direct cell-cell contact. These cytokines stimulate expression of the adhesion molecules ICAM-1, VCAM-1, and E- and P-selectin on endothelial cell surfaces and up regulate beta(2)-integrins and ICAM-1 on luminal leukocytes. White blood cells then adhere to the activated endothelial cells, migrate through the vessel wall, and penetrate areas of infection or tissue damage. The basis for a cellular immune response is formed by the interaction between T lymphocytes and antigen-presenting cells amplified by adhesion molecule LFA-1,2,3 to ICAM-1 binding. Proteins, glycoconjugates, and carbohydrate polymers are implicated in extracellular matrix formation and express multifunctionality as well as high versatility in both physiological and pathological processes, as for instance cytokine sequestration, basement membrane scaffolding, and tumor invasion and metastasis. The supramolecular architecture of basement membranes is largely dominated by self-assembly processes and specific heterophilic interactions between type IV collagen, perlecan, laminin, and entactin. These flexible thin mats are the strategic sites at which cells traverse this surface, subbase, and interfacial structure in inflammation and tumor invasion. Growth factors and other cytokines stored and cross-complexed at syndecan/perlecan low-affinity as well as PTKR-SF high-affinity binding sites interfere into these pathological scenarios. The three-step development of the invasive phenotype of cancer cells comprises cell attachment, local proteolysis, and cell migration. Adhesion is mediated by a contribution pattern of several classes of cell adhesion molecules such as vitronectin and laminin receptors amplified and ispersed over the entire cell surface. In addition, cytokine-inducible members of the immunoglobulin superfamily and the cell surface hyaluronan receptor facilitate the metastatic process in serving as tumor cell attachment sites to the vascular or lymphatic endothelium. Molecules of the cadherin family, however, suppress tumor invasion. Overexpression of E-cadherin in highly invasive clones resulted in a loss of invasive potency. Matrix metalloproteinases, constitutively overexpressed or induced by cytokines in tumor cell invasion, promote the extracellular matrix proteolysis. Growth factors such as EGF, TGF alpha, and PDGF up-regulate the transcription of interstitial collagenase and stromelysin. Moreover, the balance of active enzymes and their inhibitors (TIMPs) has shifted in favor of proteolysis. Tumor cell motility and metastatic spread are dominated by chemokinesis, chemotaxis, and haptotaxis. Matrix proteolysis and directional migration are prerequisites for intravasation, extravasation, and propagation into the target tissue. While the initial stages of metastasis encompass haptotactic migration over insoluble matrix proteins, chemotactic responses to partially degraded matrix components characterize the migratory phenotype later. Cell locomotion in eukaryotic cells resides in the cortical actin cytoskeleton which is interwoven with the cytoplasmic syndecan as well as the cell-and matrix-binding perlecan domains. Therefore, the actin-based cytoskeletal proteins a-actinin, filamin, and desmin were adsorbed as monomolecular layers to a hydrophobic silica surface in order to investigate the effect of Ca2+ ions by ellipsometry. Ca2+ ions in a concentration of 10(-4), 10(-3) and 2.52 mmol/l had no effect on the adsorbed amount, refractive index and molecular length of these individual intermediate filament proteins. Cross-linked filamin-desmin, however, reacted drastically upon calcium addition with a change in refractive index and molecular length. The 92.5 nm long filamin-desmin complex contracted by 2.5, 6.7, and 6.5 nm, respectively. The maximum shortening occurred already at 1 mu mol/l Ca2+. The Ca2+-dependent contraction of cross-linked filamin-desmin supports the contractile mechanisms in muscular tissues, and forms the basis for migration and motility in nonmuscular cells. These motional events are crucially involved in peripheral organ perfusion, inflammation, and tumor invasion and metastasis.
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| 48. |
- Siegel, G, et al.
(författare)
-
Tumor cell locomotion and metastatic spread
- 1998
-
Ingår i: Microscopy research and technique (Print). - 1059-910X .- 1097-0029. ; 43, s. 276-282
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Tidskriftsartikel (refereegranskat)abstract
- The cytoskeletal filament proteins cu-actinin, filamin, desmin, and filamin-desmin aggregates were adsorbed to a hydrophobic silica surface. The adsorbed amount as measured by ellipsometric methods after rinsing and equilibration was 2.7 mg/m(2) for alpha-actinin and 0.4 mg/m(2) for filamin plus desmin, respectively. Adsorbed layer thicknesses in physiological salt solution were about 107 nm, 89 nm, 108 nm and 93 nm for alpha-actinin, filamin, desmin, and cross-linked filamin-desmin, respectively. Ca2+ ions in a concentration of 10(-4), 10(-3), and 2.52 mmol/l had no effect on the adsorbed amount, refractive index, and adsorbed layer thickness of the individual intermediate filament proteins. Cross-linked filamin-desmin, however, reacted markedly upon the addition of these Ca2+ concentrations with a change in refractive index and adsorbed layer thickness. The layer formed by the filamin- desmin complex contracted by 2-3, 6-7, and 6-7 nm, respectively. The maximum shortening occurred at 1 mu mol/l Ca2+. The Ca2+-dependent adsorbed layer changes of cross-linked filamin-desmin supports the contractile mechanisms in muscular tissues and forms the basis for migration and motility in nonmuscular cells. These motional events are crucially involved in peripheral organ perfusion, inflammation, and tumor invasion and metastasis.
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| 49. |
- Siegel, G, et al.
(författare)
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Vascular smooth muscle, a multiply feedback-coupled system of high versatility, modulation and cell-signaling variability
- 1997
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Ingår i: Int J Microcirc. - 0167-6865. ; 17, s. 360-373
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Tidskriftsartikel (refereegranskat)abstract
- Under normal conditions, the various vascular regulatory effector influences are interwoven in a dynamic, and not a static, circulatory system. The reaction of a smooth muscle cell is thus reflected only incompletely by the stationary activation curve `developed tension versus membrane potential'. The missing time domain in this relationship is a reflection of our as yet limited understanding of the system´s behavior in space and time. It should be emphasized that rythmogenic properties of vascular smooth muscle are closely coupled to a functioning circulation.The electrical and mechanical oscillations, which can be traced back to rhythmic activity of the active electrogenic Na+K+ pump, could originate in the allosteric qualities of the enzyme phosphofructokinase (PFK).Thus, PFK represents a rhythmogenic enzyme which may serve as an example of the connection between the biological properties on a molecular level and the spatiotemporal system`s behavior.The cardiovascular system and its rhythmicity may be dominated by only a few control points, one of which is distinguished by the viscoelastic properties of a blood flow sensor macromolecule.Therefore, the three prominent control points PFK, (Na++K+)-ATPase and flow sensor conformation -acting as negatively feedback-couple nonlinear synergetic order papameter are sufficient to initiate the periodic events in the cardiovascular system and to provide a plausible explanation for their causal origin.
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| 50. |
- Stemme, S, et al.
(författare)
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Effect of colloidal silica and electrolyte on the structure of an adsorbed cationic polyelectrolyte layer
- 1999
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 155, s. 145-154
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between an adsorbed high molecular weight cationic polyacrylamide (C-PAM) and anionic components have been investigated by ellipsometry. The anionic components used were non-aggregated and microaggregated anionic colloidal silica particles (ACS) and an anionic polyacrylamide (A-PAM). The C-PAM was adsorbed to a silica surface and the different anionic components were then added to the system. The effect of adding an electrolyte (NaCl) to some of these systems was also investigated. The thickness of the adsorbed layer, the adsorbed amount and some kinetic aspects of the adsorption and desorption processes were studied. A three-fold expansion was observed for the C-PAM layer when non-aggregated and microaggregated ACS was added. When large amounts of NaCl are added there is a great decrease in layer thickness for a system with non-aggregated ACS. A system with microaggregated ACS particles is less affected by an increase in the electrolyte concentration. More ACS is adsorbed to a C-PAM layer in the presence of NaCl than in its absence. When A-PAM is added to the C-PAM layer, the thickness and adsorbed amount is much less influenced than if ACS is added. A small increase in adsorption and in layer thickness is first observed and then a desorption process starts. Information about the conformation of the adsorbed cationic polyacrylamide has also been obtained. The ellipsometry measurements indicate that the structure of the adsorbed layer changes as the adsorption process proceeds. The polymers adsorbed first to the surface give a more dense layer than the polymers adsorbed last.
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