Phase transformation of a liposomal dispersion into a micellar solution induced by drug-loading

Cytotoxic effect and mechanism inducing cell death of α-mangostin liposomes in various human carcinoma and normal cells

The aims of this study were to develop α-mangostin liposomes as well as to evaluate their physicochemical properties and cytotoxic activity. α-Mangostin liposomes were prepared using the reverse-phase evaporation method with lipid composition of phosphatidylcholine to cholesterol at 7 : 3 molar ratios; their physicochemical properties and antiproliferative activity were assessed using an MTT assay in four human carcinoma cells [that is, human lung epithelial carcinoma (Calu-3), human colon carcinoma (HT-29), human breast carcinoma (MCF-7), and human colon carcinoma (Caco-2) cells], and two human normal cells [that is, human dermal fibroblasts (HDF) and human adult low-calcium elevated temperature (HaCaT) keratinocytes]. Determinations of morphological changes and oligonucleosomal DNA fragments were also carried out. The liposomal dispersions obtained were unilamellar vesicles as confirmed by cryotransmission and freeze-fracture electron microscopy with a particle size of 114 nm and a ζ potential of -2.56 mV. The P-NMR spectra showed that α-mangostin molecules orientated in the phospholipid bilayer membrane. The α-mangostin could appreciably be entrapped with an efficiency and loading of 81 and 4%, respectively. The antiproliferative activity of α-mangostin liposomes in various cancer and normal cells showed a dose-dependent inhibition in all treated cell lines. The antiproliferative effect of α-mangostin liposomes was found to be associated with apoptosis, with differences in sensitivity among the cell lines treated.

Applications of X-ray scattering in pharmaceutical science

The use of X-ray scattering techniques in pharmaceutical science is increasing, in part through increased collaborations with the materials science community, and through increased availability of instrumentation, particularly synchrotron sources. The ability to understand not only the biopharmaceutical outcome, but also arguably, more importantly, the structural aspects of drugs and drug delivery systems, is essential to progressing pharmaceutical science; this review serves as an introduction to the major techniques and the wide range of areas in which X-ray scattering may be applied in understanding and controlling structure in pharmaceutical systems.

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.

Studies on the encapsulation of diclofenac in small unilamellar liposomes of soya phosphatidylcholine

The encapsulation of acid (AD) and sodium diclofenac (SD) in small unilamellar liposomes (SUV) as well as the interactions of the drug with the bilayer was studied. SUV was prepared by sonication from multilamellar liposomes containing soya phosphatidylcholine and diclofenac at various proportions. The size distribution obtained from dynamic light scattering showed that the incorporation of SD decreases significantly the size of the liposomes suggesting that the drug interacts with the bilayer of the liposomes. This size decrease is related with the phase transition of liposomes to mixed micelar solution. The encapsulation of the hydrophilic dye indocyanine green in the aqueous compartment of liposomes showed that the rate of captured dye decreases with SD concentration suggesting the transition of liposomes to mixed micelles. The (31)P NMR analysis indicates that SD interacts with the phosphate of phosphatidylcholine head groups. A schematic model for interaction of SD with phosphatidylcholine of the liposomes in which the diclofenac anion interacts with the ammonium group of the phospholipid and the dichlorophenyl ring occupies a more internal site of bilayer near phosphate group was proposed.

Study of the diclofenac/phospholipid interactions with liposomes and monolayers

The interaction of diclofenac sodium (SD) with soya phosphatidylcholine (SPC) has been studied with floating Langmuir monolayers and liposomes. SD was either introduced into the subphase of SPC monolayers or co-spread with SPC on an aqueous subphase. In both cases, SD caused the surface pressure isotherm to become more expanded, thus demonstrating the affinity between SD and SPC. The incorporation of SD caused SPC liposomes to have a decreased diameter according to light scattering experiments. When SPC liposomes were injected into an aqueous subphase, their destruction yielding surface-active monomers could be monitored by changes in surface pressure. SD-loaded liposomes displayed a much faster kinetics when the surface density of surface-active monomers was plotted against time, with rate constants increasing significantly with the SD concentration. The kinetic profile can be quantitatively analyzed by plotting ln[1 - (gamma/gamma infinity)] versus t1/2.

Physicochemical characterisation of liposomes with encapsulated local anaesthetics

Local anaesthetics may be added to intravenous o/w emulsions of propofol to reduce the initial pain of injection. Due to incompatibility problems of the emulsion on the addition of a local anaesthetic solution, prior encapsulation of the drug within liposomes is suggested. The liposomes were prepared with the sonication method and loaded with either lidocaine hydrochloride (LiHCl) or prilocaine hydrochloride (PrHCl). The liposomal systems were characterised with photon correlation spectroscopy (PCS) in terms of mean particle size and polydispersity. Lamellarity and lamellar thickness were determined by small angle X-ray scattering (SAXS). Visualisation of drug-loaded liposomes was performed with transmission electron microscopy (TEM) after freeze fracture replication of the samples. Depending on the manufacturing procedure mean particle sizes of the drug-free liposomes varied from 150 +/- 9 nm to 102 +/- 2 nm. Drug-loaded liposomes manufactured the same way showed reduced particle sizes of 125 +/- 1 nm and 85 +/- 7 nm, respectively. Determination of bilayer thickness by SAXS yielded 6.2 +/- 0.2 nm in the case of full hydration whereas the bilayer thickness without the hydration shell was just 4.4 +/- 0.2 nm. The small particle sizes achieved are appropriate for intravenous administration.

Surface active drugs: self-association and interaction with membranes and surfactants. Physicochemical and biological aspects

Many pharmacologically active compounds are of amphiphilic (or hydrophobic) nature. As a result, they tend to self-associate and to interact with biological membranes. This review focuses on the self-aggregation properties of drugs, as well as on their interaction with membranes. It is seen that drug-membrane interactions are analogous to the interactions between membranes and classical detergents. Phenomena such as shape changes, vesiculation, membrane disruption, and solubilization have been observed. At the molecular level, these events seem to be modulated by lipid flip-flop and formation of non-bilayer phases. The modulation of physicochemical properties of drugs by self-association and membrane binding is discussed. Pathological consequences of drug-membrane interaction are described. The mechanisms of drug solubilization by surfactants are reviewed from the physicochemical point of view and in relation to drug carrying and absorption by the organism.