Liposomes in chromatography.

The newest achievements in the application of liposomes in different chromatographic technologies such as high-performance liquid chromatography and electrically driven separation methods was compiled and critically evaluated. The employment of chromatographic methodologies for the determination of molecular parameters of biological importance is also discussed in detail. The future trends of the use of liposomes is also shortly discussed.

Studies on molecular interactions between nalidixic acid and liposomes.

The interaction between nalidixic acid sodium salt (NANa) and liposomes prepared from alpha-L-dipalmitoyl-phosphatidylcholine (DPPC) or from its binary mixture with dioleoyl-phosphatidylcholine (DOPC) was studied with differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) spectroscopy. We evaluated the role of broadband ultraviolet-B (UV-B) irradiation on the molecular interactions between the lipids and the NANa, and determined the decay-kinetics of the incorporated spin labeled fatty-acid free radicals. Multilamellar and unilamellar vesicles were prepared by sonication and extrusion. The entrapment efficiencies were determined spectrophotometrically. The size-distribution of the liposomes and its change in time was checked by dynamic light scattering (DLS). Our results indicate that NANa mainly interacts with lipid head groups. However, its effect and presumably the formation of the free radicals, induced by broadband ultraviolet-B, is not localized only to the head group region of the lipid molecules. Depending on DOPC content, interaction between the NANa and the lipids modifies the phase-transition parameters of the liposome dispersions.

Molecular interactions between DPPC and morphine derivatives: a DSC and EPR study.

The interaction between different morphine derivatives (morphine, codeine, N-methyl-morphine, N-methyl-codeine) and alpha-L-dipalmitoyl phosphatidylcholine (DPPC) liposomes was studied with differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) spectroscopy. Small unilamellar DPPC-liposomes with the given morphine-derivative were prepared by sonication. The size distribution of liposomes was checked by dynamic light scattering (DLS). The amount of entrapped morphine was determined spectrophotometrically. Our results indicate that the morphine and its derivatives principally interact with the lipid head groups, and this interaction leads to a decrease in the mobility of the polar head groups, especially in case of codeine and N-methyl-codeine.

[Preparations of liposomal morphine. Investigation of the interaction of morphine and its derivatives with the dipalmitoyl phosphatidylcholine membrane]. / Morfin liposzómába zárása. Morfinszármazékok dipalmitoil-foszfatidilkolin membránnal kialakuló kölcsönhatásának vizsgálata.

Liposomes composed of the lipids of biological membranes are suitable for drug delivery. To reach a better therapeutical effect it is important to know the properties of interactions between the drug and lipid molecules. From dipalmitoyl phosphatidylcholine (DPPC) using ultrasound small liposomes containing morphine were prepared. The amount of entrapped morphine was determined with spectrophotometry and luminescence spectroscopy. The interaction between the molecules of morphine and its derivates (codeine, N-methyl-morphine, N-methyl-codeine) and the DPPC lipid was studied with differential scanning calorimetry (DSC) and electron spin resonance (ESR) methods. Our studies indicated that the molecules of morphine and its derivates principally interact with the environment of DPPC lipid head groups. Due to the interaction the mobility of head groups decreases especially in case of codeine and N-methylcodeine.

[Liposomes as drug carrier systems. Preparation, classification and therapeutic advantages of liposomes]. / A liposzóma mint gyógyszerszállító rendszer. A liposzómák elóállítása, alapvetó típusaik és terápiás alkalmazásuk elónyei.

Bangham et al. (1965) created first the concept of the liposome as a microparticulate lipoidal vesicle separated from its aqueous environment by one or more lipid bilayers. Later Gregoriadis and Ryman (1972) suggested to use liposomes as drug carrier systems. Nowadays liposomes are under extensive investigation for improving the delivery of therapeutic agents, enzymes, vaccines and genetic materials. Liposomes offer an excellent opportunity to selective targeting of drugs which is expected to optimize the pharmacokinetical parameters, the pharmacological effect and to reduce the toxicity of the encapsulated drugs. To understand the system it is important to know the basic properties of these lipoidal vesicles. Our aim was to focus on the lipid composition and the method of liposome preparation what determine the liposomal membrane fluidity, permeability, vesicle size, charge density, steric hindrance and stability of the liposomes as principle factors those influence the fate of liposomes, their interactions with the blood components and other tissues after systemic administration or local use.

[Interaction of lipid membranes and neutral polymers by differential scanning calorimetry (DSC)]. / Lipidmembránok és neutrális polimerek kölcsönhatásának differenciál "scanning" kalorimetriás (DSC) vizsgálata.

Polymer-free and polymer-bearing liposomes from dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphatidylglycerol (DMPG) and cholesterol (Ch) 10:1:1 (w/w/w) were prepared. Polymer-bearing liposomes were formed by incorporating an uncharged polymer [poly(vinyl alcohol) (PVA), poly(vinyl alcohol-co-vinylacetal) (PVA-Al), poly(vinyl alcohol-co-vinyl propional) (PVA-Prol) poly(vinyl alcohol-co-vinyl butiral) (PVA-Bul) copolymer, polyvinyl pyrrolidone (PVP) or polyethylene glycol (PEG) respectively]. The effect of some polymers on the phase transition parameter of phospholipids (DMPC and DMPG) has been studied by differential scanning calorimetry (DSC). DSC has become a standard technique for studying the thermally induced transition of phospholipid molecules from an ordered crystalline-like state at low temperature (gel phase) to a liquid crystalline-like state at higher temperature. The interaction between phospholipids and polymers was characterized by the alteration of the phase transition parameters (Tp, Tm, delta T1/2, delta Hp, delta Hm) measured by DSC. It was observed that some phase transition parameters were affected by all polymers but in different extent. PVA-Prol copolymer exhibited a prominent effect in increasing the membrane cooperativity. The influence of PVA-Bul was unique; it decreased the cooperativity of phospholipid molecules. It was also shown that the lipid membranepolymer interaction considerably depends on both the chemical structure and the molecular mass of the polymers.

[Kinetics stability of liposomes]. / Liposzómák kinetikai állandóságának jellemzése.

Liposomes find extensive use as drug carriers. The surface characteristics of vesicles (particle size, charge, composition, hydrophobicity etc.) and also, the kinetic stability of liposomes are all key factors for controlling fundamental carrier properties, such as the encapsulation or adsorption efficiency, the organ distribution of the carrier or the RES clearance etc. Small unilamellar (SUV) vesicles of dimyristoyl-phosphatidylcholine (DMPC) were prepared under standardized conditions. The liposomes were prepared both in the absence and the presence of an uncharged polymer [polyvinyl alcohol (PVA), polyvinyl acetal (PVA1) and polyvinyl pyrrolidone (PVP) respectively] and simultaneously, the long-term (kinetic) stability of the aqueous lipid dispersions were studied. The aggregation behavior of colloidal dispersions of DMPC liposomes were tested in physiological salt solution and polymer solutions, respectively. Particle aggregation, which may take place on storage or when the stability is lowered, are well reflected in the shift of the mean size and the distribution function towards higher values. The particle sizes, the size distribution and their change in time were measured by photon correlation spectroscopy using a Malvern ZETASIZER 4 apparatus (Malvern Instruments, UK).

Role of hydrophobic and hydrophilic forces in peptide-protein interaction: new advances.

A considerable part of important biological processes is governed by the noncovalent association of peptides and proteins. Various types of intermolecular forces may be involved in the formation of these molecular assemblies. This review gives a brief account of the physicochemical bases of interactive forces, with special emphasis on their impact on various peptide-protein interactions; summarizes the newest biochemical and biophysical methods for the study of such interactions; and discusses the role of various hydrophilic and hydrophobic forces in peptide-protein interactions in various fields of life sciences, such as immunology, enzymology, receptor binding, and toxicology.

Interaction of phospholipids with proteins and peptides. New advances IV.

1. The review deals with the newest achievements in the field of the various interactions between phospholipids and proteins and peptides. 2. Interactions are classified according to the hydrophobic, hydrophilic or mixed character of the interactive forces. 3. The effect of the interaction on the structure and biological activity of the interacting molecular assemblies is also discussed.

Effect of some potassium selective crown ethers on the permeability and structure of a phospholipid membrane.

The effect of some new crown ethers on the cation efflux and phase transition parameters of dipalmitoyl phosphatidylcholine liposomes was studied. The effects were correlated with the lipophilicity of the crown ethers. The results indicate that the presence of two crown ring structures in one crown either molecule is a prerequisite for the increase of ion permeability of liposomes. The effective crown ethers decrease the temperature, enthalpy and cooperativity of the gel-to-liquid crystalline phase transition. The crown ethers increase membrane permeability for potassium and, to a lesser extent, for rubidium and sodium. The ratio of permeability increase for potassium/rubidium significantly correlates with the lipophilicity of the crown ethers.

Interaction of monoamine oxidase inhibitory drugs with some phospholipids.

The effect of 17 monoamine oxidase inhibitory drugs (propargylamine derivatives) on the phase transition parameters of some synthetic phospholipids has been studied by differential scanning calorimetry. The drugs modified the thermal behaviour of phospholipids proving the existence of phospholipid-drug interactions. Phosphatidylethanolamine, phosphatidylcholine and phosphatidic acid equally interact with the monoamine oxidase inhibitory drugs. Significant correlations were found between the change of the phase transition parameters of phospholipids and the hydrophilic and hydrophobic molecular parameters of drugs. Calculations suggest that both hydrophilic (between the head group of phospholipids and the polar propargylamine group of drugs) and hydrophobic (between the apolar fatty acid chains of phospholipids and the lipophilic substructures of drugs) forces are involved in the phospholipid-drug interaction. Chloro substitution in the hydrophobic moiety of drugs enhances considerably the strength of interaction.

Interaction of phospholipids with proteins and peptides. New advances III.

1. The review deals with the recent achievements in the study of the various interactions of phospholipids with proteins and peptides. 2. The interactions are classified according to the hydrophobic, hydrophilic or mixed character of the interactive forces. 3. The effect of the interaction on the structure and biological activity of the interacting molecules is also discussed.

Interaction of phospholipids with proteins and peptides. New advances 1990.

1. The review deals with the recent achievements in the study of the various interactions of phospholipids with proteins and peptides. 2. The interactions are classified according to the hydrophobic, hydrophilic or mixed character of the interactive forces. 3. The effect of the interaction on the structure and biological activity of the interacting molecules is also discussed.

Interaction of membrane phospholipids with some DNA substructures studied by means of differential scanning calorimetry.

The interaction of dipalmitoylphosphatidylcholine, dipalmitoylphosphatidic acid and dipalmitoylphosphatidylethanolamine with some DNA substructures such as cytidine, uridine, adenosine 5'di- and triphosphate, guanosine 5'mono- and diphosphate, cytidine 5'mono- and triphosphate, uridine 5'mono- and triphosphate and inosine 5'monophosphate was studied with differential scanning calorimetry. The dependence of pretransition and main transition temperatures and the enthalpy of main transition on the molecular characteristics of the interacting molecular species was calculated by stepwise regression analysis. Nucleosides and nucleotides increased the main transition temperature and peak half width of phospholipids and they decreased the enthalpy of main transition proving the existence of interaction between phospholipids and DNA substructures. Calculation proved that the interaction is mainly of hydrophilic character but the involvement of hydrophobic forces or steric conditions cannot be ruled out.

Differential scanning calorimetry to study the possible ternary complex formation between chlorhexidine, phosphatidylcholine and some nonionic tenzides.

The effect of chlorhexidine and its molecular complexes with some nonionic tenzides (Tween and Myrj series) on the phase transfer parameters of dipalmitoylphosphatidylcholine has been studied by differential scanning calorimetry. The application of principal component analysis facilitated the evaluation of the experimental data matrix. It was found that both the lipophilicity of the tenzide and the strength of interaction between chlorhexidine and nonionic tenzide had a considerable impact on some of the phase transition parameters of dipalmitoylphosphatidylcholine. These findings indicate the possible existence of ternary complexes. This ternary complex formation may cause a decrease of chlorhexidine activity in the presence of nonionic tenzides.

Hydrophobic interaction between tryptophan and some synthetic nucleosides.

The interaction of 29 synthetic nucleosides with tryptophan was studied by charge-transfer reversed-phase thin-layer chromatography and the relative strength of interaction was calculated. In the majority of cases Trp significantly decreased the lipophilicity of the nucleosides. This effect may be due to the interaction between the more hydrophilic Trp and the more lipophilic nucleosides, resulting in charge-transfer complexes of moderate lipophilicity. Stepwise regression analysis proved that the length of the alkyl substituent of nucleosides significantly influences the strength of interaction. Our findings supports the hypothesis that the nucleosides turn toward Trp with their alkyl substituent and the binding is of hydrophobic character.

Interaction of phospholipids with proteins, peptides and amino acids. New advances 1987-1989.

1. The review deals with the recent achievements in the study of the various interactions of phospholipids with proteins, peptides and amino acids. The interactions are classified according to the hydrophobic, hydrophilic or mixed character of the interactive forces. The effect of the interaction on the structure and biological activity of the interacting biomolecules is discussed.

Determination of the lipophilicity of some peptides. Effect of surface pH of silica.

The lipophilicities of 22 peptides were determined by reversed-phase thin-layer chromatography using methanol as organic modifier in the concentration range 0-90 vol.-% on silica supports with surface pH values of 2.0,4.5,6.0,7.5 and 9.0. Only one of the 22 peptides (Trp-Ala-Ile) followed the general rule, i.e., its RM value decreased linearly with increasing proportion of organic modifier over the whole concentration range. Most peptides exhibited typical silanophilic retention behaviour, the RM value decreasing with increasing organic phase concentration in the lower concentration range and then increasing with further increase in the proportion of organic modifier. In some instances the lipophilicity increased linearly with increasing proportion of methanol. The silanophilic effect depended not only on the structure of the peptide, but also on the surface pH of the silica support. The retention behaviour of peptides can be well described by a polynomial function, the linear and quadratic forms of methanol concentration and surface pH being the independent variables. Principal component analysis showed that the presence of a ring structure in the peptides has the greatest impact on their retention behaviour, the overall polarity (basic, neutral or acidic) being of secondary importance. The number of amino acids in the peptide has a negligible effect on the chromatographic behaviour.

Study of chlorhexidine-tenside interactions by means of charge-transfer chromatography.

The interactions of chlorhexidine with 42 nonionic tensides were studied by means of charge-transfer reversed-phase thin-layer chromatography. The alkyl chain of chlorhexidine interacted with the alkyl chains in the hydrophobic part of the tensides, while the ethylene oxide groups of the tensides interacted with the polar guanidine groups of chlorhexidine. These two types of interaction (hydrophobic and hydrophilic) are probably not independent of each other.

Hydrophilic interactions between charged amino acids and the effect of ions on the strength of interaction.

The interaction between oppositely charged amino acids was studied by charge-transfer reversed-phase thin-layer chromatography. The dependence of the lipophilicity of Arg, Lys and Orn on the concentration of Glu, Asp, Gln and Asn in the eluent was considered to be related to the strength of interaction. The interaction of dibasic amino acids with Glu and Asp was stronger than with Gln and Asn. Mono- (Li+, Na+, K+, Rb+ and Cs+) and divalent (Mg2+ and Ca2+) cations decreased the strength of interaction suggesting the electrostatic character of the interaction. Their inhibitory effect mainly depended on their concentration and to a lesser extent on the ion charge and hydrated ion radii. Stepwise regression analysis proved that the strength of interaction depends on the polarity parameters of amino acids and is independent of their chemical structure.