Biomedical subjects

Björn Lindman

Publications and source records attributed to Björn Lindman.

28 records · Page 2Linked to original sources

PubMed2005

Electrophoretic properties of complexes between DNA and the cationic surfactant cetyltrimethylammonium bromide.

We use agarose gel electrophoresis to characterize how the monovalent catioinic surfactant cetyltrimethylammonium bromide (CTAB) compacts double-stranded DNA, which is detected as a reduction in electrophoretic DNA velocity. The velocity reaches a plateau at a ratio R = 1.8 of CTAB to DNA-phosphate charges, i.e., above the neutralization point, and the complexes retain a net negative charge at least up to R = 200. Condensation experiments on a mixture of two DNA sizes show that the complexes formed contain only one condensed DNA molecule each. These CTAB-DNA globules were further characterized by time-resolved measurements of their velocity inside the gel, which showed that CTAB does not dissociate during the migration but possibly upon entry into the gel. Using the Ogston-model for electrophoresis of spherical particles, the measured in-gel velocity of the globule is quantitatively consistent with CTAB having two opposite effects, reduction of both the electrophoretic charge and DNA coil size. In the case of CTAB the two effects nearly cancel, which can explain why opposite velocity shifts (globule faster than uncomplexed DNA) have been observed with some catioinic condensation agents. Dissociation of the complexes by addition of anionic surfactants was also studied. The DNA release from the globule was complete at a mixing ratio between anionic and cationic surfactants equal to 1, in agreement with equilibrium studies. Circular DNA retained its supercoiling, and this demonstrates a lack of DNA nicking in the compaction-release cycle which is important in DNA transfection and purification applications.

Cetrimonium↗

PubMed2005

Prevention of postoperative peritoneal adhesions: effects of lysozyme, polylysine and polyglutamate versus hyaluronic acid.

OBJECTIVE: Intraperitoneal adhesions are an important cause of postoperative intestinal obstruction, abdominal discomfort and infertility. In the present study we hypothesized that a combination of polypeptides with different surface properties, resulting in fine disperse low-soluble complexes, could be of benefit in the prevention of abdominal adhesions. MATERIAL AND METHODS: Various polypeptides including lysozyme, polyglutamate, polylysine and combinations of all three were evaluated as compared to hyaluronic acid. A standard wound on the parietal peritoneum in mice was used and the evaluated agents were administered immediately postoperatively. The extent of peritoneal adhesions to the injured area was measured and expressed as a percentage of the wound length as evaluated after 7 days. Flow cytometry was performed to evaluate the effect on peritoneal macrophage survival and phagocytic function and the Pick test was used to determine peroxide production in order to estimate toxicity and potential impairment of macrophage function caused by the chemicals. RESULTS: Significant differences were seen among the treatment groups (p<0.001). Both polyglutamate and lysozyme, and polyglutamate together with polylysine significantly decreased adhesion formation as compared to hyaluronic acid. The polylysine-polyglutamate combination was still visible macroscopically on the peritoneal surface after 1 week, though not after 1 month. The polyglutamate-lysozyme mixture was less effective than these individual components alone. The chemicals did not show any toxic effects or altered function in macrophage cell culture. CONCLUSIONS: Lysozyme, polyglutamate and, most effectively, a polyglutamate-polylysine combination significantly decreased experimental abdominal adhesion formation. A strong mechanical connection to the wound and prolonged attendance in the surface were noted. Peritoneal phagocyte function did not seem to be influenced by the chemicals.

Adjuvants, Immunologic↗

PubMed2004

DNA and cationic surfactant complexes at hydrophilic surfaces. An ellipsometry and surface force study.

The adsorption and formation of DNA and cationic surfactant complexes at the silica-aqueous interface have been studied by ellipsometry. The interaction between the DNA-surfactant complexes at the mica-aqueous interface has been determined by the interferometric surface force apparatus. Adsorption was as expected not observed on negatively charged hydrophilic surfaces for DNA and when DNA-cationic surfactant complexes were negatively charged. However, adsorption was observed when there is an excess of cationic surfactant, just below the point of phase separation. The adsorption process requires hours to reach steady state. The adsorbed layer thickness is large at low surface coverage but becomes more compact and thinner at high coverage. A long-range repulsive force was observed between adsorbed layers of DNA-cationic surfactant complexes, which was suggested to be of both electrostatic and steric origin. The forces were found to be dependent on the equilibration time and the experimental pathway.

Adsorption↗

PubMed2004

Adsorption of cationic cellulose derivative/anionic surfactant complexes onto solid surfaces. II. Hydrophobized silica surfaces.

The effect of the anionic surfactant SDS (sodium dodecyl sulfate) on the adsorption behavior of cationic hydroxyethyl cellulose (Polymer JR-400) and hydrophobically modified cationic cellulose (Quatrisoft LM-200) at hydrophobized silica has been investigated by null ellipsometry and compared with the previous data for adsorption onto hydrophilic silica surfaces. The adsorbed amount of LM-200 is found to be considerably larger than the adsorbed amount of JR-400 at both surfaces. Both polymers had higher affinity toward hydrophobized silica than to silica. The effect of SDS on polymer adsorption was studied under two different conditions: adsorption of polymer/SDS complexes from premixed solutions and addition of SDS to preadsorbed polymer layers. Association of the surfactant to the polymer seems to control the interfacial behavior, which depends on the surfactant concentration. For the JR-400/SDS complex, the adsorbed amount on hydrophobized silica started to increase progressively from much lower SDS concentrations, while the adsorbed amount on silica increased sharply only slightly below the phase separation region. For the LM-200/SDS complex, the adsorbed amounts increased progressively from very low SDS concentrations at both surfaces, and no large difference in the adsorption behavior was observed between two surfaces below the phase separation region. The complex desorbed from the surface at high SDS concentrations above the critical micelle concentration. The reversibility of the adsorption of polymer/SDS complexes upon rinsing was also investigated. When the premixed polymer/SDS solutions at high SDS concentrations (>5 mM) were diluted by adding water, the adsorbed amount increased due to the precipitation of the complex. The effect of the rinsing process on the adsorbed layer was determined by the hydrophobicity of the polymer and the surface.

Adsorption↗

PubMed2004

Influence of DNA adsorption and DNA/cationic surfactant coadsorption on the interaction forces between hydrophobic surfaces.

The forces between hydrophobic surfaces with physisorbed DNA are markedly and irreversibly altered by exposure to DNA/cetyltrimethylammonium bromide (CTAB) mixtures. In this colloidal probe atomic force microscopy study of the interactions between a hydrophobic polystyrene particle and an octadecyltrimethylethoxysilane-modified mica surface in sodium bromide solutions, we measure distinct changes in colloidal forces depending on the existence and state of an adsorbed layer of DNA or CTAB-DNA complexes. For bare hydrophobic surfaces, a monotonically attractive approach curve and very large adhesion are observed. When DNA is adsorbed at low bulk concentrations, a long-range repulsive force dominates the approach, but on retraction some adhesion persists and DNA bridging is clearly observed. When the DNA solution is replaced with a CTAB-DNA mixture at relative low CTAB concentration, the length scale of the repulsive force decreases, the adhesion due to hydrophobic interactions greatly decreases, and bridging events disappear. Finally, when the surface is rinsed with NaBr solution, the length scale of the repulsive interaction increases modestly, and only a very tiny adhesion remains. These pronounced changes in the force behavior are consistent with CTAB-induced DNA compaction accompanied by increased DNA adsorption, both of which are partially irreversible.

Adsorption↗

PubMed2004

Network formation of catanionic vesicles and oppositely charged polyelectrolytes. Effect of polymer charge density and hydrophobic modification.

In nonequimolar solutions of a cationic and an anionic surfactant, vesicles bearing a net charge can be spontaneously formed and apparently exist as thermodynamically stable aggregates. These vesicles can associate strongly with polymers in solution by means of hydrophobic and/or electrostatic interactions. In the current work, we have investigated the rheological and microstructural properties of mixtures of cationic polyelectrolytes and net anionic sodium dodecyl sulfate/didodecyldimethylammonium bromide vesicles. The polyelectrolytes consist of two cationic cellulose derivatives with different charge densities; the lowest charge density polymer contains also hydrophobic grafts, with the number of charges equal to the number of grafts. For both systems, polymer-vesicle association leads to a major increase in viscosity and to gel-like behavior, but the viscosity effects are more pronounced for the less charged, hydrophobically modified polymer. Evaluation of the frequency dependence of the storage and loss moduli for the two systems shows further differences in behavior: while the more long-lived cross-links occur for the more highly charged hydrophilic polymer, the number of cross-links is higher for the hydrophobically modified polymer. Microstructure studies by cryogenic transmission electron microscopy indicate that the two polymers affect the vesicle stability in different ways. With the hydrophobically modified polymer, the aggregates remain largely in the form of globular vesicles and faceted vesicles (polygon-shaped vesicles with largely planar regions). For the hydrophilic polycation, on the other hand, the surfactant aggregate structure is more extensively modified: first, the vesicles change from a globular to a faceted shape; second, there is opening of the bilayers leading to holey vesicles and ultimately to considerable vesicle disruption leading to planar bilayer, disklike aggregates. The faceted shape is tentatively attributed to a crystallization of the surfactant film in the vesicles. It is inferred that a hydrophobically modified polyion with relatively low charge density can better stabilize vesicles due to formation of molecularly mixed aggregates, while a hydrophilic polyion with relatively high charge density associates so strongly to the surfactant films, due to strong electrostatic interactions, that the vesicles are more perturbed and even disrupted.

Journal Article↗

PubMed2003

Mechanism of formation of DNA-cationic vesicle complexes.

Cationic vesicles and DNA form complexes that are promising gene delivery systems. Despite the increasing number of publications on their morphology and structure, the mechanism leading to their formation is not yet understood due to a lack of kinetic data. In the present study the kinetics of the interaction between DNA and cationic vesicles were followed using stopped-flow turbidity and small-angle neutron scattering techniques. The neutron real-time experiments were performed on a high-flux diffractometer, the D22 at the ILL, using a stopped-flow set-up. Extruded mixed vesicles of dimethyldioctadecylammonium bromide (DODAB) with various amounts of dioleoylphosphatidylethanolamine (DOPE) were investigated at 25 degrees C. The results show that the transition from unilamellar vesicles to a multilamellar structure upon DNA addition occurs in three steps. The first step, on the millisecond time scale, is currently not accessible to neutron scattering but was observed by stopped-flow turbidity and fluorescence experiments. The second step, on a time scale of seconds, corresponds to the formation of an intermediate with a locally cylindrical structure. As time progresses this unstable intermediate evolves to a multilamellar structure, on a time scale of minutes. An understanding of the mechanisms behind the DNA-cationic vesicle complex formation event will allow the production of more homogeneous, efficient delivery systems in pharmaceutically acceptable forms.

DNA↗

PubMed2002

Effect of pharmaceutically acceptable glycols on the stability of the liquid crystalline gels formed by Poloxamer 407 in water.

The ability of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers (Poloxamers) to form "gels" (lyotropic liquid crystalline structures) in water is of interest to pharmaceutical applications. In such applications the presence of polar organic solvents is often desirable or required. The effect of such solvents on the stability of lyotropic liquid crystalline gels formed by PEO-PPO-PEO block copolymers was assessed by studying the phase behavior and structure in ternary isothermal (25 degrees C) systems of pharmaceutical interest consisting of Poloxamer 407 (EO(100)PO(70)EO(100)), water, and one of the following solvents (referred to here collectively as "glycols"): glycerol, propylene glycol, ethanol, polyethylene glycol 400, and glucose. Small-angle X-ray scattering was employed to establish the structure of the liquid crystals obtained and to determine their characteristic length scales. The stability range of the liquid crystalline gel phases in the systems studied was found to vary with the glycol type. For example, the micellar cubic structure can accommodate about 0.85:1 parts glucose per part water (in terms of weight) and up to as much as 5.5:1 parts propylene glycol per part water. A correlation between the glycol effects on the stability of the liquid crystalline phases and glycol physiochemical characteristics such as octanol/water partition coefficient or solubility parameter is proposed.

Gels↗

PubMedDate not supplied

Interaction between DNA and charged colloids could be hydrophobically driven.

The interaction of DNA with amino-functionalized polystyrene particles has been studied by using a dynamic light scattering (DLS) technique. In 10 mM NaBr solution the particles have a hydrodynamic radius of 76 nm and the DNA macromolecule investigated (double stranded) has a hydrodynamic radius of 107 nm. At very low DNA concentrations, DNA adopts a flat conformation on the particle surface. If the DNA concentration is increased above 0.1 microg/mL, the thickness of the DNA layer increases, suggesting the presence of large loops and tails. Although the particles contain primary amino groups, they have a negative net charge under the conditions used in this work. Thus, the driving force for DNA adsorption is not of electrostatic origin but rather due to a hydrophobic effect. Addition of cationic surfactant to the DNA-precoated amino-functionalized particles induces changes in the adsorbed layer conformation, in agreement with the coadsorption of cationic surfactant.

Adsorption↗

PubMedDate not supplied

DNA-cationic surfactant interactions are different for double- and single-stranded DNA.

The stability of DNA in solution and the phase behavior in mixtures with dodecyltrimethylammonium bromide (DTAB) were investigated. By means of circular dichroism, UV absorption, and differential scanning calorimetry, we found that for dilute solutions of DNA with no addition of salt the DNA molecules are in the single-stranded conformation, whereas the addition of a small amount of NaBr, 1 mM, is sufficient to stabilize the DNA double-helix. Furthermore, at higher DNA concentrations, native DNA becomes the most stable structure, which is due to a self-screening effect. By phase diagram determinations of the DNA-surfactant system, we found that the effect of salt on phase behavior mainly relates to a difference in interaction of the amphiphile between single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). The difference in association between ss and dsDNA with surfactants of different chain lengths can be interpreted in terms of an interplay between hydrophobic and electrostatic interactions, the latter being influenced by polymer flexibility. In this way, a nonmonotonic variation can be rationalized. A crossing of the phase separation lines with DNA concentration can be rationalized in terms of a change in relative stability of ss and dsDNA. The fact that ssDNA phase separates earlier than dsDNA in association with DTAB, may serve as a basis for a method of easily separating dsDNA from ssDNA by the addition of surfactant; this is verified as monitored by circular dichroism measurements.

Calorimetry, Differential Scanning↗