Liposomal membrane. I. Chemical damage of liposomal membranes with functional detergent

Polysaccharide-Coated Immunoliposomes Bearing Anti-CEA Fab' Fragment and Their Internalization by CEA-Producing Tumor Cells

Immunoliposomes, bearing Fab' fragments of anti-carcinoembryonic antigen (anti-CEA) monoclonal antibody, have been prepared according to a new method developed in our laboratory. First, egg phosphatidylcholine liposomes were coated with pullulan derivatives. Then, SH-bearing Fab' fragments of anti-CEA were conjugated to the pullulan derivatives attached to the liposomal surface. These immunoliposomes showed specific binding to CEA-producing cells, BM314, which was approximately 20-fold greater than to CEA-non- producing cells, RPMI #4788. In addition, these immunoliposomes were endo cytosed by colon cancer cells, which was confirmed by fluorescence microscopy using liposomes labelled by a hydrophobic fluorescent probe, terbium trisace tylacetonate.

Role of phospholipids in drug-LDL bindings as studied by high-performance frontal analysis/capillary electrophoresis

The binding study between basic drugs ((S)-verapamil (VER) and (S)-propranolol (PRO)) and phospholipid liposomes was performed by using high-performance frontal analysis/capillary electrophoresis (HPFA/CE) in order to investigate the effect of oxidative modification of low-density lipoprotein (LDL) upon drug-binding affinity from molecule-based viewpoint. 1-Palmitoyl-2-oleoyl-phosphatidylcholine (POPC, 16:0, 18:1), 1-palmitoyl-2-linoleoyl-phosphatidylcholine (PLPC, 16:0, 18:2), dilauloyl-phosphatidylcholine (DLaPC, 12:0, 12:0), 1-palmitoyl-2-oleoyl-phosphatidyl-glycerol (POPG, 16:0, 18:1), and 1-palmitoyl-sn-glycero-3-phosphocholine (monoPPC, 16:0) were used to prepare the model liposomes. At physiological pH (pH 7.4), the model liposome prepared from POPG+POPC had negative net charges, while the total net charge of the other model liposomes (POPC liposome, PLPC liposome, DLaPC liposome, and monoPPC+POPC liposome) was zero. The drug and the model liposome mixed solutions were subjected to HPFA/CE, and the total binding affinities (nK) were calculated. The nK values of VER and PRO to POPG+POPC liposome were more than six and 10 times higher than those of other liposomes, respectively. On the other hand, the nK values of the model drugs to POPC liposome, PLPC liposome, DLaPC liposome and monoPPC+POPC liposome showed small differences less than twice. These results indicate that the electrostatic interaction plays an important effect on drug-liposome binding, and suggest that the increase in the negative charge of LDL phospholipids gives more significant effect on the drug-binding affinity of the basic drugs than the acyl-chain structure.

Effect of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its toxic metabolites on the physicochemical property of the liposomal membrane in relation to their cytochrome P-450 inhibition

The effects of the neurotoxin MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and its toxic metabolites MPDP+ (1-methyl-4-phenyl-2,3-dihydropyridinium) and MPP+ (1-methyl-4-phenylpyridinium) on liposomal membrane were assessed using fluorescence-polarization and carboxyfluorescein leakage studies as well as in biological membrane preparations. Of the three compounds, MPTP was found to cause the greatest perturbation of membrane followed by MPDP+ and then MPP+. The ability of the three toxins to inhibit cytochrome P-450 enzyme activity (a microsomal membrane-bound enzyme system) was also studied and their relative potency was again found to be MPTP > MPDP+ > MPP+. The changes in the physicochemical property of the liposomal membrane can be related to the ability of the neurotoxin's ability to inhibit cytochrome P-450 activity.

Synthesis and characterization of 1,2-dimyristoylamido-1, 2-deoxyphosphatidylcholine as an artificial boundary lipid

The synthesis and characterization of an artificial boundary lipid, 1,2-dimyristoylamido-1,2-deoxyphosphatidylcholine (DDPC), are described. DDPC has two amide bonds instead of ester bonds of regular lecithins such as 1,2-dimyristoylphosphatidylcholine (DMPC). In differential scanning calorimetry (DSC) measurements, DDPC gave two endothermic peaks: one was at 18.0 degrees C (delta H = 10.74 kJ.mol-1) and the other at 23.0 degrees C (delta H = 12.91 kJ.mol-1). The former peak was sharp and considered to be the phase transition of the hydrocarbon region, while the latter was assigned to the melt of the hydrogen-belt formed by the amide groups of DDPC. Addition of DDPC to DMPC made the DMPC membrane less fluid in the region close to the surface, and significantly increased the reconstitution efficiency of glycophorin into the membrane. This effect of DDPC was much larger than that of naturally occurring lipid, sphingomyelin.

The mechanism of liposomal damage by taurocholate

The stability of small unilamellar vesicles formed by egg-yolk phosphatidylcholine (PC) has been examined in the presence of sodium taurocholate. The permeability of the vesicular membrane changes as the total taurocholate concentration increases, until a transformation from mixed bile salt/PC vesicles to mixed micelles occurs. Based on experiments in which the bile salt-induced release of either hydrophilic (carboxyfluorescein) or hydrophobic (Bromothymol blue) probes was studied, and on fluorescence polarization of the probe 1,6-diphenyl-1,3,5-hexatriene and turbidity measurements, a two-step process for the initial stage of liposomal damage by taurocholate is postulated.

A newly developed immunoliposome--an egg phosphatidylcholine liposome coated with pullulan bearing both a cholesterol moiety and an IgMs fragment

An improved methodology for providing a more stable and targetable drug carrier has been developed. This method involves the synthesis of a newly designed immunoliposome by coating the outermost surface of large oligolamellar vesicles of egg phosphatidylcholine with the polysaccharide pullulan, modified to carry both cholesterol, as the hydrophobic anchor, and the monoclonal antibody fragment (anti-sialosyl Lewis X, IgMs) as the sensory device. Compared with the binding of pullulan-coated liposomes, that of this immunoliposome to specific cells in vitro was significantly increased by factors of 447 to PC-9 and 295 to KATO-III, but only by a factor of 148 to the less specific cell, 3LL. This strong and specific binding of the immunoliposome to the cell surface of PC-9 was also confirmed by a fluorescence-microscopic investigation using the immunoliposome, which bore the hydrophobic fluorescent probe, terbium trisacetylacetonate, in the liposomal membrane.

Bile salt damage of egg phosphatidylcholine liposomes

Physiochemical damage of egg phosphatidylcholine liposomes, caused by the salts of three bile acids, chenodeoxycholic acid, ursodeoxycholic acid, and cholic acid, has been investigated. Of the three bile salts, that of chenodeoxycholic acid was the most destructive, and the effect of the damage was examined by monitoring the induced 6-carboxyfluorescein release from the liposomes. For all three of the bile salts and under the experimental conditions, the minimum (effective) concentrations causing the 6-carboxyfluorescein release were below their critical micelle concentrations. In the case of the salt of chenodeoxycholic acid, the presence of cholesterol in the liposomal bilayers did not show any significant effect on the induced 6-carboxyfluorescein release, while, for the salts of ursodeoxycholic acid and cholic acid, the presence of cholesterol tended to depress the release. Permeation of bile salts into the membranes of liposomal bilayers made these membranes more fluid, and this fluidity was monitored by measuring the change in fluorescence polarization using 1,6-diphenylhexatriene entrapped in the liposomes. Coating the liposomes with polysaccharides, to make them more hydrophobic, led to their easier lysis by the bile salts.

Liposomal membranes. XIV. Fusion of liposomal membranes induced by polyisoprenoids as monitored by fluorescence quenching method

Fusion of the single-walled liposomes of egg phosphatidylcholine as induced by the polyisoprenoids such as solanesol, trans-ethyl decaprenoate (EDP), coenzyme Q10, and dolichol has been investigated adopting the fluorescence quenching method. Relative efficiency of the polyisoprenoids employed on the induced fusion of liposomes was a sequence of solanesol less than or equal to EDP much less than CoQ10, dolichol, which was consistent with the result previously obtained by the dye-release method.

Liposomal membranes. XI. A suggestion to structural characteristics of acido-thermophilic bacterial membranes

To understand the role of omega-cyclohexyl fatty acid residue of lipids in acido-thermophilic bacterial membranes, three unusual phosphatidylcholines, 1, 2-di-11-cyclohexylundecanoyl-L-alpha-phosphatidylcholine (11CYPC), 1,2-di-13-cyclohexyltridecanoyl-L-alpha-phosphatidylcholine (13CYPc), and 1-13-cyclohexyltridecanoyl-2-11-cyclohexylundecanoyl-L-alpha- phosphatidylcholine (1-13CY-2-11CYPC) were prepared and the steady-state fluorescence anisotropy of 1, 6-diphenylhexatriene (DPH) in the hydrophobic domain of these liposomal bilayers was determined. Compared with the case of dipalmitoyl (DPPC) or dimyristoyl phosphatidylcholine (DMPC), introducing the omega-cyclohexyl moiety onto lecithins makes the bilayers fluid below the phase transition temperature, while immobilizes them above the phase transition temperatures. The properties of the unusual phosphatidylcholine liposomes suggested by the steady-state fluorescence anisotropy investigation were in good agreement with those obtained from the thermotropic and permeability investigations. Results obtained are discussed from the view point of the role and function of lipid membranes of acido-thermophilic bacteria which contain unusual fatty acids.