Jan Cocquyt

A successful strategy for the production of cationic magnetoliposomes

Summary The present work describes a strategy and the mechanistic background for synthesizing magnetoliposomes (MLs) in which the bi-layered coating is partly composed of positively charged lipids. In a first step, neutral MLs are prepared from zwitterionic phosphatidylcholine vesicles and magnetite nanocores stabilized with an anionic surfactant, and then incubated with cationic vesicles formed from phosphatidylcholine and dioleoyltrimethylammoniumpropane. During this latter step, spontaneous intermembrane lipid transfer occurs. After reaching an equilibrium state, the desired cationic MLs are captured from the mixture in a high-gradient magnetophoresis setup.

Quantifying wetting and wicking phenomena in cotton terry as affected by fabric conditioner treatment.

To enable the simultaneous determination of both the speed and extent of liquid absorption in cotton fabrics, we have developed a radial, horizontal wicking experiment. The initial part of the absorbed mass versus time profile is linear, which allows us to determine the wicking rate. After a given time, a constant mass is reached, corresponding to the liquid absorption capacity of the fabric. Using the method proposed, we show that a fabric conditioner does not affect the physical characteristics. such as porosity and pore size, and hence the water absorption capacity of cotton terry. On the other hand, there is a pronounced effect on the wicking rate. Based on the experimentally determined values of the contact angle of water on the treated fabrics, the differences in wicking rates as a function of the kind of fabric conditioner can be ascribed to differences in wettability.

Evaluation of the interaction of propranolol with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes: the Langmuir model.

The interaction of the amine containing beta-receptor blocking agent propranolol (Ppn) with dimyristoylphosphatidylcholine (DMPC) vesicles was studied. Using a centrifugation assay, the protonated as well as unprotonated amount of the drug sorbed was verified, whereas the binding of the protonated Ppn was deduced from the surface charge density of the vesicles as calculated from electrophoretic mobility measurements. Assuming a 1:1 binding, a Langmuir model with only two parameters was found to be sufficient to fit all experimental data. Sensitivity analysis revealed that the estimated values of these parameters were reliable and independent from each other. These parameters were truly intrinsic, as electrostatic interactions were accounted for in the model. It was found that the pKa of Ppn shifted from 9.24, when dissolved in water, downward by 1.34 units upon sorption, indicating that the intrinsic partition coefficient of the unprotonated Ppn was about 22 times higher than that of the protonated analog. In addition, a significant increase in the affinity of both Ppn analogs with increasing salt concentration was found. Theoretical analysis revealed that the Langmuir sorption model may be considered as a partitioning model with decreasing partition coefficient as the sorbed amount increases. Thus, the Langmuir model provides a better fit than a simple partition model at conditions that induce a substantial amount of propranolol sorbed, such as high pH and high propranolol concentrations.

Design and Development of Magnetoliposome-Based Theranostics

Magnetoliposomes (MLs) consist of nanometre-sized magnetite cores, enwrapped by a bilayer of phospholipid molecules. In the past we showed that these nanocolloids can be exploited as powerful biocompatible magnetic resonance imaging (MRI) contrast agents. In the present work, we report on the partitioning of the amphiphilic drug, (R/S)-propranolol, within the lipidic envelope of MLs, built up of the zwitterionic dimyristoylphosphatidylcholine. Furthermore, it is also shown that MLs are easily internalized by 3T3 fibroblasts, used in this study as a representative cell model, without damaging cell viability. Overall, the results deliver the proof-of-concept that drug-loaded MLs have great potential as unique intracellular theranostics, i.e., as a nanoscale delivery system with combinatory therapeutic-diagnostic imaging modalities.

PEGylation of phospholipids improves their intermembrane exchange ratePresented at the 17th Conference of the European Colloid & Interface Science Society, Firenze, Italy, September 21?26, 2003.

The polar headgroup of dimyristoylphosphatidylethanolamine (DMPE) was modified by attaching a hydrophilic polymer-amino acid complex and the effects of this modification on the non-protein-mediated transfer features of the lipid determined. The first step in the organic synthesis protocol was the conversion of α,ω-dicarboxy poly(ethylene glycol) into its anhydride form, followed by attachment of the molecule to the amino group of DMPE. In the second step, the remaining free –COOH group on the polymer terminus was activated consecutively with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and sulfo-N-hydroxysuccinimide, and then coupled to tryptophan. The purified conjugate was mixed with dipentadecanoylphosphatidylglycerol (1/9 molar ratio) and sonicated to produce small unilamellar vesicles. These vesicles (donors) were then mixed with dipentadecanoylphosphatidylglycerol magnetoliposomes (acceptors) and the transfer kinetics of the modified lipid followed, using high-gradient magnetophoresis as the fractionation technique. The transfer behavior of non-modified DMPE was also examined. The first-order kinetic plots, corrected for back exchange lipid movement, showed that hydrophilization of DMPE dramatically improved its transfer capacity. These findings are explained by considering the thermodynamical consequences of the exchange process. The possibility of using biomolecule-derivatized phospholipids to trigger physiological effects in biological cells is briefly discussed.