Interactions between Starburst Dendrimers and Mixed DMPC/DMPA-Na Vesicles Studied by the Spin Label and the Spin Probe Techniques, Supported by Transmission Electron Microscopy

Abstract

The interactions between polyamidoamine starburst dendrimers (SBDs) and vesicles consisting of dimyristoylphosphatidylcholine (DMPC) and its phosphatidylcholate salt (DMPA-Na) in various relative ratios (from 0% to 40% of DMPA-Na) were studied by electron paramagnetic resonance (EPR) and by transmission electron microscopy (TEM). The EPR spectra were computer-simulated to extract mobility and structural parameters of the probes and labels. The systems were analyzed as a function of the level of protonation of SBDs and generation (G ) 2SBD and G ) 6SBD). Both the hydrophobic 5doxylstearic spin probe (5DSA) and the positively charged nitroxide CAT16, a cationic surfactant with a C16 chain, inserted in the vesicles and monitored the formation of dendrimer-mixed vesicle (DMPC/DMPA-Na) complexes. 5DSA revealed a partial ordering of a double-layer-like structure occurring at the dendrimer surface. The spin labels at the vesicle/dendrimer interface modified the structural and mobility parameters upon complexation with the dendrimer. At high levels of protonation, dendrimers showed a larger interaction with the vesicles, especially for the mixed vesicles, compared to dendrimers at a lower level of protonation. In agreement with EPR results, TEM micrographs showed that the addition of DMPA-Na to DMPC modifies the vesicle shape from spherical to rodlike. The EPR analysis suggested that the vesicles wrap around the large dendrimers whereas the small dendrimer directly interacts with the vesicle surface. The results are very promising for a better understanding of the mechanism of interaction of dendrimers with cell membranes which may be an important feature in the role of SBDs as drug and gene carriers to target cells.

The breakdown of bilayer lipid membranes by dendrimers

“…Under our conditions, the PC molecules forming the BLMs are in the gel phase. The interaction between the positively charged PAMAM G5 dendrimer and the lipid membrane can induce the formation of holes (as was shown for PAMAM G7 dendrimers [17]), the inclusion of dendrimers into the lipid membrane and the disturbance of the bilayer (the formation of hexagonal phases, and so on) [4][5]17], or, in some cases, the exiting of lipid molecules from the bilayer and the formation of dendrimer-lipid vesicles [18]. Furthermore, as polyelectrolytes, PAMAM dendrimers (like proteins and DNA) are able to form domains in a bilayer [19].…”

“…All these reasons explain the 10-to 100-fold differences in dendrimer concentrations. Electrostatic forces are predominant in interactions between dendrimers and lipid bilayers [4,5,17,18], so the neutral PAMAM-OH G5 dendrimer cannot effectively interact with zwitterionic phosphatidylcholine-forming BLMs. One of the possible reasons for the absence of effective interactions between the anionic PAMAM G4.5 dendrimer and BLMs is the formation of different concentrations of LH + and LOH -forms of phosphatidylcholine [22], which can also disturb the effective binding of Ca 2+ ions by the phosphatidylcholine monolayer above pH 6.5 [22,23].…”

“…Their unique properties permit their application in targeting, microarray systems, catalysis and drug delivery systems [3][4][5]. Polyamidoamine (PAMAM) dendrimers are based on an ethylenediamine core and branched units built from methyl acrylate and ethylenediamine.…”

“…The interaction between dendrimers and lipids, liposomes or lipid membranes is an important issue in need of study. Lipid-dendron assemblies and lipid dendrimers are successfully used in medicine for the overall uptake of drugs through membranes [3][4][5]. The technique of voltammetry is extensively used with bilayer lipid membranes (BLMs) to study different interactions [6][7][8][9].…”

Influence of dendrimers on red blood cells

“…3). Interactions between dendrimers and the lipid bilayer have been studied using many methods such as EPR techniques [26][27][28], leakage, lipid mixing and content mixing assays [29][30][31], differential scanning calorimetry [32,33], and atomic force microscopy [34]. Loss of integrity of the RBC membrane which may occur under the influence of dendrimers is accompanied by haemoglobin leakage, which can be measured.…”