Properties of immobilized-liposome-chromatographic supports for interaction analysis

Photodynamic inactivation of viruses by immobilized chlorin-containing liposomes

The viral safety of blood derived products relies in properly chosen inactivation procedures. In this way, it has been reported that some photosensitizers are useful products for blood sterilization. The data presented here show the high incorporation efficiency of the chlorin 3-phorbinepropanol, 9,14-diethyl-4,8,13,18-tetramethyl-20-(3S-trans) (CHL) into anionic unilamellar liposomes, give a protocol for the steric immobilization of chlorin-containing liposomes in a chromatographic support and provide the studies of photodynamic inactivation of bovine viral diarrhea virus (BVDV) and encephalomyocarditis virus (EMCV) with chlorin-containing liposomes, free in solution and immobilized on Sephacryl S-1000 beads. The study demonstrates the successful inactivation of the enveloped virus BVDV by both preparations in culture medium and the resistance of the non-enveloped virus EMCV. The effectiveness of CHL-containing liposomes, in solution and immobilized in the chromatographic support, decreased when the culture media was replaced with human blood plasma. Moreover, the reduction factor of the virus titer after irradiation was smallest when immobilized liposomes were used. Nevertheless, the reduction factor for the virus titers of enveloped viruses after irradiation of human blood plasma samples with immobilized chlorin-containing liposomes increased with the reduction of the sample thickness. The more outstanding aspect of this paper is the design of a system useful for blood sterilization that can be easily removed after photodynamic treatment and, therefore, able to be applied in the manufacturing processes.

Quantitative structure-retention relationships for ionic and non-ionic compounds in biopartitioning micellar chromatography

Quantitative structure-retention relationships, QSRRs, represent a powerful tool in chromatography. The objectives of QSRR studies are to predict the chromatographic retention behaviour of solutes based on their structural properties, to elucidate retention mechanisms, to optimize the separation of complex mixtures or to prepare experimental designs. In this paper, using the retention factors of 151 structurally unrelated solutes that cover a wide range of hydrophobicity, molecular size, hydrogen bonding properties and ionization degrees obtained in biopartitioning micellar chromatography (BMC) at different Brij35 micellar concentrations, several multivariate QSRR models are tested. It is demonstrated that the chromatographic retention of any molecule in BMC, independently of its family, can be adequately described by its hydrophobicity (expressed as log P) and its anionic and cationic total molar charge (expressed as alpha(A) and alpha(B)).

Effects of ions and detergents in drug partition chromatography on liposomes

We have determined drug partitioning into phospholipid bilayers by immobilized-liposome chromatography (ILC). Electrostatic effects on the drug partitioning were observed on neutral bilayers at low ionic strength. The size of the counterions affected the partitioning. When liposomes were supplemented with ionic detergents the partitioning of charged drugs was strongly affected, allowing complete separation of drugs of different charges which showed similar retention on neutral bilayers. Partial separation was obtained on bilayers containing fatty acid. Detergent ions or fatty acid inserted into phospholipid bilayers affected the partitioning of drugs much more than did free ions or phospholipid head group charges.

Simple coating of capillaries with anionic liposomes in capillary electrophoresis

A new and relatively simple method was developed for coating of capillaries in electrophoresis with liposomes. The liposomes, with a diameter of about 100 nm, are large unilamellar vesicles prepared by extrusion. The liposomes contained 1-palmitoyl-2-oleyl-sn-glycero-3-phosphatidylcholine (POPC) or POPC with different proportions of bovine brain phosphatidylserine (PS) and cholesterol. They formed a bilayer structure on the silica surface enabling the separation of neutral compounds. The effectiveness of the coating in separation was evaluated with use of uncharged steroids as model compounds. The coating was also studied by measuring the electroosmotic flow. The best results, taking into consideration both separation and stability, were achieved with anionic 80:20 mol% POPC/PS liposomes. In addition, the effect of coating conditions on the results was investigated. Among the buffers studied [N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) (HEPES), phosphate, tris(hydroxymethyl)aminomethane (Tris) and N-tris(hydroxymethyl)methylglycine (Tricine)], HEPES seemed to have a significant effect on the success of the coating. Successful separation of steroids was achieved only when HEPES buffer was used in the coating procedure and in the background electrolyte solution for the separation. With all other buffers the peaks of the model compounds overlapped.

Affinity electrochromatography of acidic drugs using a liposome-modified capillary

Liposomes can be effectively deposited on the inner surface of a capillary wall by flushing the electrophoretic system with a liposome suspension followed by air-drying of the capillary and removal of the excess of loosely bound liposomes by a 0.1 M NaOH wash. It was demonstrated that capillaries prepared in this way could be used for studies of analyte (drug)-liposome binding. The results were expressed as free binding energy changes [delta(deltaG0)] relatively to an arbitrarily selected standard (acetylsalicylic acid). The results were compared to [delta(deltaG0)] changes obtained from binding studies effected by capillary electrophoresis using a stable liposome plug in a capillary with minimized endoosmotic flow. Good agreement of data reported in the literature (without correction for the residual endoosmotic flow), our previous data obtained in a similar way (however, after the correction for the residual endoosmotic flow) and data obtained by the immobilized liposome affinity electrochromatography reported in this communication was achieved.

Centrifugal and chromatographic analyses of tryptophan and tyrosine uptake by red blood cells and GLUT1 proteoliposomes with permeability estimates and observations on dihydrocytochalasin B

We analyzed transport into liposomes and proteoliposomes, separated the free and internalized radioactively labeled substrates by size-exclusion chromatography (SEC) and observed a net influx owing to nonfacilitated diffusion across the lipid bilayers during the separation. The permeabilities (10(-9) cm/s) of glucose transporter (GLUT1) proteoliposomes were estimated to be 4.6, 1.0, 1.4 and 2.1 for D-glucose, L-glucose, L-Tyr and L-Trp, respectively; 15, 3.3, 5.1 and 2.1 times higher than the corresponding permeabilities of liposomes. These values indicated that GLUT1 did not transport Tyr or Trp, or transported Tyr, and only Tyr, slowly. This interpretation was supported by further analyses. Dihydrocytochalasin B inhibited the transport of Tyr and, partially, Trp into human red blood cells (centrifugal analyses). It did not inhibit Tyr and Trp influx into GLUT1 proteoliposomes, but partitioned strongly into the bilayers and seemed to make them fragile. The GLUT1 inhibitor cytochalasin B and the GLUT1 substrate 2-deoxy-D-glucose did not inhibit Tyr transport into the cells. Upon immobilized biomembrane affinity chromatography, Trp decreased the cytochalasin B retardation by GLUT1 only at levels far above the physiological Trp concentration. Ethanol (commonly added to aqueous solutions for enhancing a compound's solubility) halved the retardation at 4% (v/v) concentration. Drastic modification of the SEC method is required to allow permeability measurements with nonlabeled and highly permeable substrates.

Immobilized-biomembrane affinity chromatography for binding studies of membrane proteins

Analyses of specific interactions between solutes and a membrane protein can serve to characterize the protein. Frontal affinity chromatography of an interactant on a column containing the membrane protein immobilized in a lipid environment is a simple and robust approach for series of experiments with particular protein molecules. Regression analysis of the retention volumes at a series of interactant concentrations shows the affinity of the protein for the interactant and the amount of active binding sites. The higher the affinity, the fewer sites are required to give sufficient retention. Competition experiments provide the affinities of even weakly binding solutes and the non-specific retention of the primary interactant. Hummel and Dreyer size-exclusion chromatography allows complementary analyses of non-immobilized membrane materials. Analyses of the human facilitative glucose transporter GLUT1 by use of the inhibitor cytochalasin B (radioactively labeled) and the competitive substrate D-glucose (non-labeled) showed that GLUT1 interconverted between two states, exhibiting one or two cytochalasin B-binding sites per two GLUTI monomers, dependent on the membrane composition and environment. Similar analyses of a nucleoside transporter, a photosynthetic reaction center, nicotinic acetylcholine receptors and a P-glycoprotein, alternative techniques, and immobilized-liposome chromatographic approaches are presented briefly.

Effects of cholesterol and model transmembrane proteins on drug partitioning into lipid bilayers as analysed by immobilized-liposome chromatography

We have analysed how cholesterol and transmembrane proteins in phospholipid bilayers modulate drug partitioning into the bilayers. For this purpose we determined the chromatographic retention of drugs on liposomes or proteoliposomes entrapped in gel beads. The drug retention per phospholipid amount (the capacity factor Ks) reflects the drug partitioning. Cholesterol in the bilayers decreased the Ks value and hence the partitioning into the membrane in proportion to the cholesterol fraction. On average this cholesterol effect decreased with increasing temperature. Model transmembrane proteins, the glucose transporter GLUT1 and bacteriorhodopsin, interacted electrostatically with charged drugs to increase or decrease the drug partitioning into the bilayers. Bacteriorhodopsin proteoliposomes containing cholesterol combined the effects of the protein and the cholesterol and approached the partitioning properties of red blood cell membranes. For positively charged drugs the correlation between calculated intestinal permeability and log Ks was fair for both liposomes and bacteriorhodopsin-cholesterol proteoliposomes. Detailed modeling of solute partitioning into biological membranes may require an extensive knowledge of their structures.

Development of predictive retention-activity models of butyrophenones by biopartitioning micellar chromatography

The predictive and interpretative capability of quantitative chromatographic retention-biological activity models is supported by the fact that in adequate experimental conditions the solute partitioning into the chromatographic system can emulate the solute partitioning into lipid bilayers of biological membranes, which is the basis of drug and metabolite uptake, passive transport across membranes and bioaccumulation. The use of retention data obtained in biopartitioning micellar chromatography (BMC) has been demonstrated to be helpful in describing the biological behaviour of different kinds of drugs. In this chromatographic system, polioxyethylene 23 lauryl ether Brij35 micellar mobile phases and C(18) reversed stationary phase in adequate experimental conditions are used. The RP-HPLC capacity factors of butyrophenones were determined using different Brij35 concentrations as micellar mobile phases. Relationships between seven biological activities of butyrophenones reported in bibliography and retention data were established and their predictive and interpretative ability evaluated. These relationships were significant between preclinical pharmacology and therapeutic efficacy parameters and the retention factors of butyrophenones (0.89 < R(2) < 0.98). The results indicate that the retention of compounds in BMC is capable of describing and predicting in vitro the biological activities of butyrophenones. This approach can be very useful in the development of new neuroleptic drugs, avoiding the use of experimental animals.

Characterization of dynamically prepared phospholipid-modified reversed-phase columns

We have modified a reversed-phase (RP8) column by passing through it an aqueous solution of phosphatidylcholine-based liposomes. The phospholipids from the liposomes adsorb onto the octyl chain of the stationary phase, thus altering the nature of the stationary phase and of the chromatographic interactions. The properties of the phospholipid-modified column were investigated using solutes belonging to several chemical classes. We found that the retention factors of negatively and positively charged solutes decreased as the amount of phospholipid in the column was increased. For the solutes studied here the extent of the decrease was smaller for the positive solutes. With neutral solutes, the retention factors of some (benzenediols) increased markedly while with others (ketones) the retention factors decreased. The selectivities between the various solutes on the phospholipid-modified column were different than on the original reversed-phase column. The retention behavior of the solutes can be explained in terms of (1) effective shielding of the hydrophobic part of the stationary phase by the polar head groups of the phospholipids and (2) hydrogen bond formation between the solutes and the carbonyl oxygens as well as the non-ester phosphate oxygens in the polar head groups of the phospholipids.

Retention-property relationships of anticonvulsant drugs by biopartitioning micellar chromatography

Epilepsy may be considered as a group of disorders with only one thing in common: the fact that recurrent anomalous electrochemical phenomena appear in the central nervous system. Different classes of drugs are included under the generic term of anticonvulsant drugs. All of them work by decreasing discharge propagation in different ways. Biopartitioning micellar chromatography (BMC) is a mode of reversed-phase liquid chromatography, which can be used as an in vitro system to model the biopartitioning process of drugs when there are no active processes. In this paper, relationships between the BMC retention data of anticonvulsant drugs, their pharmacokinetics (oral absorption, protein binding, volume of distribution, clearance, and renal elimination) and their therapeutic parameters (therapeutic, toxic and comatose-fatal concentration, and LD50) are studied and the predictive ability of models is evaluated.

Non-ionic micellar affinity capillary electrophoresis for analysis of interactions between micelles and drugs

Micellar affinity capillary electrophoresis (MACE) was introduced to evaluate the affinity of various kinds of drugs as benzoic acid, salicylic acid, trinitrophenol, p-hydroxybenzoic acid and o-acetylsalicylic acid. Non-ionic micelles as Brij 35 (polyethylenglycol dodecylether), Tagat (polyoxyethylene (20) glycerol monooleate) and Tween 20 (polyoxyethylen sorbitan monolaurate) were used as a pseudostationary phase in capillary electrophoresis. For polyvinyl alcohol (PVA) coated capillary was used in this examinations. The drugs had negative electrophoretic mobilities at a pH value of pH 7.2. The negatively charged drugs migrated toward the anode and were related by their interaction with the micelles. The difference in the mobility of the drugs owing to the presence of the micelles reflected the interaction between these drugs and the micelles. Equations were derived to calculate the capacity factor k' from the migration times in the presence of micelles t' and in the absence of micelles t, the partition coefficients Pwm and the Gibbs free energy. The drugs show different interaction and affinity with the micelles in the systems. Strong interaction was observed between benzoic acid and the micelles. Furthermore, a linear relationship (R = 0.999) was obtained between deltaG(o) and ln Pwm in the micellar solubilization of drugs. These results show that deltaG(o) can give us information on the affinity and on the partition behaviour of the drugs in these systems.

Chromatographic retention of drug molecules on immobilised liposomes prepared from egg phospholipids and from chemically pure phospholipids

The partitioning of a chemically diverse set of drugs into liposomes was studied by immobilised liposome chromatography (ILC). For this purpose liposomes composed of (i) purified egg phospholipids (EPL), (ii) synthetic phosphatidylcholine (PC), (iii) PC--synthetic phosphatidylethanolamine (PE) 80:20 (mol/mol) and (iv) PC--synthetic phosphatidylserine (PS) 80:20 (mol/mol) were immobilised in gel beads by freeze-thawing. The drug partitioning was assessed from the retention volume, which was expressed as a capacity factor, K(s), normalised with respect to the amount of immobilised phospholipid. The drug retention on EPL, PC and PC--PE liposomes was very similar, whereas the negatively charged PC--PS liposomes increased the retention of positively charged and decreased retention of negatively charged drugs. The partitioning of drugs on liposome columns (log K(s)) versus their octanol--water partitioning (log P(oct)) showed three separate rectilinear relationships, depending on the charge of the compound (neutral, positive, or negative). Statistical analysis (ANCOVA) proved that the lines had similar slopes. Repeated analysis of four reference compounds showed a low variation (<0.12 log units) over time (about 250 days). A close relationship was observed between the drug retention in short EPL columns with a low content of phospholipids and the retention in longer standard EPL columns. The short 'quick screen bilayer columns' permit analysis of highly lipophilic compounds within 30 min and are thus applicable for medium-throughput screening in drug discovery settings. A very strong rectilinear relationship (r(2)=0.95, n=13) between log K(s) (EPL) and published liposome partitioning data (log D(mem)) confirmed that the ILC drug retention reflects the drug partitioning into the lipid bilayers. A moderate to fair rectilinear relationship was observed between the normalised retention on PC, PC-PE and EPL liposomes (r(2)=0.79, 0.86 and 0.85, respectively, n=24) and corresponding published log k'(IAM) data obtained on immobilised artificial membrane (IAM) columns. Transport across Caco-2 cell monolayers (log P(c)) showed curvilinear relationships with log K(s), log k'(IAM), log P(oct) and log D(oct). The drug fraction absorbed in humans showed a similar relationship to log K(s) values as to surface plasmon resonance signals representing drug-liposome interaction (Danelian et al., 2000 J Med Chem, 43, 2083--2086).

Freeze-thaw immobilization of liposomes in chromatographic gel beads: evaluation by confocal microscopy and effects of freezing rate

Biological membranes immobilized in chromatographic gel beads constitute a multifunctional affinity matrix. Membrane protein-solute interactions and drug partitioning into the lipid bilayers can conveniently be studied. By the use of confocal laser-scanning microscopy (CLSM) the distribution of immobilized model membranes in the beads has been visualized for the first time. Freeze-thaw-immobilized liposomes in Superdex 200 gel beads were situated in a thick shell surrounding a liposome-free core. The amount of phospholipids immobilized by freeze-thawing was dependent on the temperature in the cooling bath and the type of test tube used. A bath temperature of -25 degrees C gave higher immobilization yield than freezing at -75 or -8 degrees C did. Freeze-thawing in the presence of liposomes did not affect the gel bead shape or the refractive index homogeneity of the agarose network of the beads, as shown by confocal microscopy.

Development of predictive retention-activity relationship models of non-steroidal anti-inflammatory drugs by micellar liquid chromatography: comparison with immobilized artificial membrane columns

The predictive and interpretative capability of quantitative chromatographic retention-biological activity models is supported by the fact that under adequate experimental conditions the solute partitioning into chromatographic system can emulate the solute partitioning into lipid bilayers of biological membranes, which is the basis for drug and metabolite uptake, passive transport across membranes and bioaccumulation. The use of micellar solutions of Brij35 as mobile phases in reversed-phase liquid chromatography has proven to be valid to predict some biological activities of different kinds of drugs. In this study, quantitative retention-activity relationship (QRAR) models to describe some of the biological activities and pharmacokinetic properties of non-steroidal anti-inflammatory drugs (NSAIDs) with predictive and interpretative ability are obtained. These models are compared with those obtained using immobilized artificial membrane (IAM) column data taken from the literature. For NSAIDs, the statistical characteristics of the micellar liquid chromatography (MLC) QRAR models were better than or at least comparable to those of the IAM-QRAR models.

Development of predictive retention-activity relationship models of antipsychotic drugs by micellar liquid chromatography

The predictive and interpretative capability of quantitative chromatographic retention-biological activity models is supported by the fact that in adequate experimental conditions the solute partitioning into the chromatographic system can emulate the solute partitioning into lipid bilayers of biological membranes, which is the basis of drug and metabolite uptake, passive transport across membranes and bioaocumulation. The use of micellar solutions of Brij35 as mobile phases in reversed liquid chromatography has proven to be valid in predicting some biological activities of different kinds of drugs. In this paper, the correlations between the logarithm of capacity factors and pharmacokinetic, preclinical pharmacology and therapeutic efficacy parameters of phenothiazines are studied. Parabolic quantitative retention-activity relationship models with predictive and interpretative ability have been obtained.

Development of predictive retention-activity relationship models of tricyclic antidepressants by micellar liquid chromatography

The distribution of tricyclic antidepressants from plasma to brain, where these drugs exert their main clinical action, and other organs is related to transport events across the cell membranes of the different tissues. It could be expected that all the molecular features that condition the transport processes (mainly hydrophobicity and molar total charge) also control the pharmacokinetic and biochemical behavior. Micellar liquid chromatography (MLC) has been proposed to emulate in vitro the partitioning process in the biomembranes. The use of micellar solutions of Brij35 as mobile phases in reversed-phase liquid chromatography has proven to be valid to predict the biological activities of local anesthetics, barbiturates, catecholamines, and benzodiazepines. In this paper, the relationships between the capacity factor in MLC and some pharmacokinetic parameters and biological responses of tricyclic antidepressants are studied. Predictive regression models for the estimation of these parameter values, using the logarithm of the retention data (log k) as independent variable, are also proposed.

Immobilized biomembrane chromatography of highly lipophilic drugs

Drug interaction with lipid bilayers was quantified by immobilized biomembrane chromatography on a series of columns containing different small amounts of human red cell membrane vesicles to extend and characterize this technique, which shows a potential for drug screening and prediction of drug absorption in humans. The chromatographic retention volume for each drug was essentially proportional to the amount of immobilized lipid, and the slope equalled the capacity factor (Ks) previously determined on single columns. Gel beds containing 0.5-2 micromol of membrane phospholipid allowed analysis of drugs with log Ks values of 2.5-4.3 in time periods of 1 min to 1 h. Highly lipophilic drugs could thus be analyzed conveniently in aqueous buffer.

Chromatographic approaches to liposomes, proteoliposomes and biomembrane vesicles

Size-exclusion chromatography has been used for fractionation of liposomes, proteoliposomes and biomembrane vesicles of up to approximately 500 nm in size and for separation of these entities from smaller components. Liposome sizes, encapsulation stability, and solute affinities for membrane proteins have been determined. Counter-current distribution in aqueous two-phase systems has widened the range of applications to larger structures. Immobilized biomembrane vesicles and (proteo)liposomes provide stationary phases for chromatographic analysis of specific or nonspecific membrane-solute interactions.

Avidin-biotin immobilization of unilamellar liposomes in gel beads for chromatographic analysis of drug-membrane partitioning

To construct a homogeneous lipid membrane chromatographic phase, biotinylated unilamellar liposomes of small and large sizes (SUVs and LUVs, respectively) were immobilized in avidin- or streptavidin-derived gel beads in amounts up to 55 micromol phospholipid/ml gel bed at yields above 50%. The immobilized liposomes exhibited excellent stability due to avidin-biotin multiple-site binding. The trapped volume and size distribution of the immobilized liposomes (0.33-0.42 microl/micromol lipid and 20-30 nm diameter for SUVs, 1.7-1.9 microl/micromol lipid and 80-120 nm for LUVs) indicated the unilamellarity and integrity of the immobilized liposomes. Partitioning of 15 pharmaceutical drugs into the bilayers of LUVs immobilized in different gel matrices correlated very well, as shown by chromatographic drug retention analysis. The partitioning of several beta-blockers into the immobilized LUVs showed a close correlation with their partitioning, reported in the literature, into free liposomes. The avidin-biotin-immobilized unilamellar liposomes can thus be used for chromatographic analysis and screening of solute-membrane interactions.

Chromatography on cells and biomolecular assemblies

Red cells, biomembrane vesicles, proteoliposomes and liposomes non-covalently immobilized in gel particles or beads have been used as stationary phases for biomembrane affinity analyses and ion-exchange chromatographic separation. Lipid monolayers coupled to silica beads have been utilized for membrane protein purification in detergent solution and plant cell walls for group separation of macromolecules according to size and charge. Further methodological studies are essential to implement general practical application.

Immobilized liposome chromatography of drugs on capillary continuous beds for model analysis of drug-membrane interactions

Liposomes were immobilized in capillary continuous beds with covalently linked C4 or C8 alkyl ligands for chromatographic analysis of drug interaction with phospholipid bilayers, as reflected by drug retention volumes and calculated differences in interaction free energies. This procedure is a high-resolution micro-scale version of immobilized liposome chromatography for prediction of diffusion of drugs across biological membranes. The logarithm of the specific capacity factors of several structurally unrelated drugs showed a linear correlation with the logarithm of known apparent drug permeabilities through Caco-2 epithelial cell monolayers. The latter values are used for prediction of absorption of orally administered drug doses.