| 1. |
- Dias, R, et al.
(författare)
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DNA-lipid systems. A physical chemistry study
- 2002
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Ingår i: Brazilian Journal of Medical and Biological Research. - 0100-879X. ; 35:5, s. 509-522
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that the interaction of polyelectrolytes with oppositely charged surfactants leads to an associative phase separation; however, the phase behavior of DNA and oppositely charged surfactants is more strongly associative than observed in other systems. A precipitate is formed with very low amounts of surfactant and DNA. DNA compaction is a general phenomenon in the presence of multivalent ions and positively charged surfaces; because of the high charge density there are strong attractive ion correlation effects. Techniques like phase diagram determinations, fluorescence microscopy, and ellipsometry were used to study these systems. The interaction between DNA and catanionic mixtures (i.e., mixtures of cationic and anionic surfactants) was also investigated. We observed that DNA compacts and adsorbs onto the surface of positively charged vesicles, and that the addition of an anionic surfactant can release DNA back into solution from a compact globular complex between DNA and the cationic surfactant. Finally, DNA interactions with polycations, chitosans with different chain lengths, were studied by fluorescence microscopy, in vivo transfection assays and cryogenic transmission electron microscopy. The general conclusion is that a chitosan effective in promoting compaction is also efficient in transfection.
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| 2. |
- Antunes, Filipe, et al.
(författare)
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A rheological investigation of the association between a non-ionic microemulsion and hydrophobically modified PEG. Influence of polymer architecture
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 215:1-3, s. 87-100
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Tidskriftsartikel (refereegranskat)abstract
- ydrophobically modified polymers (HM-P) typically behave as thickeners in a wide range of systems. The thickening effect in an aqueous solution of this kind of polymer depends on intermolecular hydrophobic associations and also on chain entanglements if the polymer concentration is significantly above the overlap concentration. In the present investigation a rather short end-capped polymer has been investigated at concentrations that are significantly below the overlap concentration. Despite the rather low polymer concentration, polymer chains were connected into a three-dimensional network by using microemulsion droplets as cross-linking points. The simple structure of the solution simplifies interpretations of results since chain entanglements can be expected to be of low importance and only intermolecular hydrophobic associations have to be considered. In particular the rheological response is in most cases well characterized by one single relaxation time and, then, the solution can be rationalized withi the framework of the Maxwell model. We have found that the length of the polymer chain's hydrophobic end-groups, as well as the temperature, have a large influence on dynamics of the system, while the length of the hydrophilic mid-block has a relatively small significance. On the other hand, the connectivity in the system depends critically on the microemulsion concentration. Thus, a maximum was found in viscosity as a function of volume fraction, interpreted as being due to a decrease in crosslink lifetime. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 3. |
- Antunes, Filipe, et al.
(författare)
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Network formation of catanionic vesicles and oppositely charged polyelectrolytes. Effect of polymer charge density and hydrophobic modification
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:11, s. 4647-4656
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Barreleiro, Paula, et al.
(författare)
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Mechanism of formation of DNA-cationic vesicle complexes
- 2003
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1364-5498. ; 122, s. 191-201
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Tidskriftsartikel (refereegranskat)abstract
- 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 25degreesC. 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.
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| 5. |
- Barreleiro, Paula, et al.
(författare)
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The kinetics of DNA-cationic vesicle complex formation
- 2003
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 107:25, s. 6208-6213
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Tidskriftsartikel (refereegranskat)abstract
- Stopped-flow fluorescence studies were performed to investigate the kinetics of formation of complexes between DNA and cationic vesicles. We followed the kinetics as a function of charge ratio and lipid vesicle composition. Binary mixtures of a saturated cationic lipid, dioctadecyldimethlammonium bromide (DODAB), and a zwitterionic lipid, dioleoylphosphatidylethanolamine (DOPE), were used to prepare small unilamellar vesicles at 25 degreesC. The binding followed first-order reactions and occurred stepwise. The results presented indicate the existence of a three-step mechanism for cationic vesicle "binding" to DNA: first DNA rapidly ads rbs onto the oppositely charged membrane surface (milliseconds), and thereafter, on a longer time scale (seconds), the formed DNA-lipid complex continues to aggregate and grow; a third step is also observed, which seems to be due to rearrangement of the complex with a further change of the DNA conformation. The time constant of each step was determined by the relative amounts of DNA and cationic vesicles and the composition of the lipid bilayer of the vesicles.
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| 6. |
- Bergh, Jonas, et al.
(författare)
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Tailored fluorouracil, epirubicin, and cyclophosphamide compared with marrow-supported high-dose chemotherapy as adjuvant treatment for high-risk breast cancer : A randomised trial
- 2000
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Ingår i: The Lancet. - 0140-6736 .- 1474-547X. ; 356:9239, s. 1384-1391
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Tidskriftsartikel (refereegranskat)abstract
- Background: Chemotherapy drug distribution varies greatly among individual patients. Therefore, we developed an individualised fluorouracil, epirubicin, cyclophosphamide (FEC) regimen to improve outcomes in patients with high-risk early breast cancer. We then did a randomised trial to compare this individually tailored FEC regimen with conventional adjuvant chemotherapy followed by consolidation with high-dose chemotherapy with stem-cell support. Methods: 525 women younger than 60 years of age with high-risk primary breast cancer were randomised after surgery to receive nine cycles of tailored FEC to haematological equitoxicity with granulocyte colony-stimulating factor (G-CSF) support (n=251), or three cycles of FEC at standard doses followed by high-dose chemotherapy with cyclophosphamide, thiotepa, and carboplatin (CTCb), and peripheral-blood stem-cell or bone-marrow support (n=274). Both groups received locoregional radiation therapy and tamoxifen for 5 years. The primary outcome measure was relapse-free survival, and analysis was by intention to treat. Findings: At a median follow-up of 34.3 months, there were 81 breast-cancer relapses in the tailored FEC group versus 113 in the CTCb group (double triangular method p=0.04). 60 deaths occurred in the tailored FEC group and 82 in the CTCb group (log-rank p=0.12). Patients in the CTCb group experienced more grade 3 or 4 acute toxicity compared with the tailored FEC group (p<0.0001). Two treatment-related deaths (0.7%) occurred in the CTCb group. Six patients in the tailored FEC group developed acute myeloid leukaemia and three developed myelodysplastic syndrome. Interpretation: Tailored FEC with G-CSF support resulted in a significantly improved relapse-free survival and fewer grade 3 and 4 toxicities compared with marrow-supported high-dose chemotherapy with CTCb as adjuvant therapy of women with high-risk primary breast cancer.
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| 7. |
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| 8. |
- Bilalov, Azat, et al.
(författare)
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Mixing oil and water by a DNA-based surfactant
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:39, s. 15408-15414
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Tidskriftsartikel (refereegranskat)abstract
- The self-assembly behavior of a cationic surfactant (dodecyltrimethylammonium) with DNA as counterion in mixtures of water and decanol was investigated. The phase diagram was established and the different regions of the phase diagram characterized with respect to microstructure by H-2 NMR (D2O), small-angle X-ray scattering (SAXS), and other techniques. The DNA-cationic surfactant aggregate is virtually insoluble in water but shows a high solubility in decanol; in decanol, highly viscous solutions/rubberlike solid material is found. In the presence of both solvents, there is a formation of liquid crystalline phases. Both lamellar and reversed hexagonal phases are found, the former favored by higher water contents, the latter by higher concentrations of decanol. The liquid crystalline phases are in equilibrium, via two-phase and three-phase regions, with the essentially pure components.
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| 9. |
- Braem, Alan, et al.
(författare)
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Influence of DNA adsorption and DNA/cationic surfactant coadsorption on the interaction forces between hydrophobic surfaces
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:15, s. 6407-6413
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Tidskriftsartikel (refereegranskat)abstract
- 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 octadecyl-trimethylethoxysilane-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.
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| 10. |
- Cárdenas, Marité, et al.
(författare)
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DNA and cationic surfactant complexes at hydrophilic surfaces. An ellipsometry and surface force study
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:20, s. 8597-8603
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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