Biomedical subjects

B Wetzer

Publications and source records attributed to B Wetzer.

3 recordsLinked to original sources

PubMed2000

Reduction-sensitive lipopolyamines as a novel nonviral gene delivery system for modulated release of DNA with improved transgene expression.

We have designed and synthesized original cationic lipids for modulated release of DNA from cationic lipid/DNA complexes. Our rationale was that modulated degradation of the lipids during or after penetration into the cell could improve the trafficking of DNA to the nucleus resulting in increased transgene expression. The new reduction-sensitive lipopolyamines (RSL) harbor a disulfide bridge within different positions in the backbone of the lipids as biosensitive function. A useful synthetic method was developed to obtain, with very good yields and reproducibility, unsymmetrical disulfide-bridged molecules, starting from symmetrical disulfides and thiols. The new lipopolyamines are good candidates as carriers of therapeutic genes for in vivo gene delivery. To optimize the transfection efficiency in these novel series, we have carried out structure-activity relationship studies by placing the disulfide bridge at different positions in the backbone of the cationic lipid and by systematic variation of lipid chain length. Results indicate that the transfection level can be modulated as a function of the location of the disulfide bridge in the molecule. We suggest that an early release of DNA during or after penetration into the cell, probably promoted by reduction of a disulfide bridge placed between the polyamine and the lipid, implies a total loss of transfection efficiency. On the other hand, proper modulation of DNA release by inserting the disulfide bridge between one lipid chain and the rest of the molecule brings about increased transfection efficiency as compared to previously described nondegradable lipopolyamine analogues. Finally, preliminary physicochemical characterization of the complexes demonstrates that DNA release from complexes can be modulated as a function of the surrounding reducing conditions of the complexes and of the localization of the disulfide bridge within the lipopolyamine. Our results suggest that RSL is a promising new approach for gene delivery.

Animals↗

PubMed1999

Bacterial S-layer protein coupling to lipids: x-ray reflectivity and grazing incidence diffraction studies.

The coupling of bacterial surface (S)-layer proteins to lipid membranes is studied in molecular detail for proteins from Bacillus sphaericus CCM2177 and B. coagulans E38-66 recrystallized at dipalmitoylphosphatidylethanolamine (DPPE) monolayers on aqueous buffer. A comparison of the monolayer structure before and after protein recrystallization shows minimal reorganization of the lipid chains. By contrast, the lipid headgroups show major rearrangements. For the B. sphaericus CCM2177 protein underneath DPPE monolayers, x-ray reflectivity data suggest that amino acid side chains intercalate the lipid headgroups at least to the phosphate moieties, and probably further beyond. The number of electrons in the headgroup region increases by more than four per lipid. Analysis of the changes of the deduced electron density profiles in terms of a molecular interpretation shows that the phosphatidylethanolamine headgroups must reorient toward the surface normal to accommodate such changes. In terms of the protein structure (which is as yet unknown in three dimensions), the electron density profile reveals a thickness lz approximately 90 A of the recrystallized S-layer and shows water-filled cavities near its center. The protein volume fraction reaches maxima of >60% in two horizontal sections of the S-layer, close to the lipid monolayer and close to the free subphase. In between it drops to approximately 20%. Four S-layer protein monomers are located within the unit cell of a square lattice with a spacing of approximately 131 A.

Amino Acids↗

PubMed1997

S-layer stabilized solid support lipid bilayers.

This work describes composite structures composed of lipid bilayer or tetraetherlipid monolayer films attached to solid supports with associated crystalline bacterial cell surface layers (S-layers). The bilayer system was established by making use of the strong chemisorption of a first monolayer of thiolipids (1-octadecanethiol or 1,2-dimyristoyl-sn-glycero-3-phosphothioethanol) on gold and attaching a second monolayer of 1,2-dipalmitoyl-sn-3-phosphatidylethanolamine by the Langmuir Schaefer technique. The tetraetherlipid monolayer was composed of Glycerol-dialkyl-nonitol tetraetherlipid (GDNT). The monolayer of GDNT exhibits the thickness of a bilayer with hydrophilic headgroups on both sides and a hydrophobic inner part. Isolated S-layer protein from Bacillus sphaericus (CCM2177, which was injected into the subphase of an LB-trough, recrystallized into a coherent monolayer at the solid supported phospholipid bilayer and at the tetraehtherlipid monolayer. The composite lipid/S-layer structures were stable enough to allow lifting from the air-water interface, rinsing in water, and transfer into a scanning force microscope.

Bacillus↗