Binding and uptake of liposomes containing a poly(ethylene glycol) derivative of cholesterol (stealth liposomes) by the macrophage cell line J774: influence of PEG content and its molecular weight

The binding and intake of liposomes containing a different molar content and chain length of a PEG-Chol derivative had been studied in cultured macrophage cell line J774. The decrease in binding and endocytosis of the liposomes containing PEG-Chol is dependent on (i) the PEG chain length, (ii) the molar content of the surfactant, (iii) the liposome concentration in the external medium. The best results in reducing the uptake of liposomes were obtained by a PEG-Chol liposome suspension with a high molar content (25%) which presents a non negligible amount of free PEG-Chol. Moreover, we could show an increase by 2 for binding and by about 5 for endocytosis of filtrated-liposomes containing 25 mol% of 8800PEG-Chol, in the absence of free PEG-Chol in the suspension. Binding and intake of control liposomes was also inhibited in the presence of free PEG-Chol. Fluid phase endocytosis of SRh was inhibited up to 45% of control in the presence of liposomes containing PEG-Chol or free PEG-Chol. Based on the comparison of 4400PEG-Chol with the most commonly used PEG derivative 5000PEG-PE, PEG-Chol is more powerful in terms of reducing their binding and endocytosis by J774 cells. Inhibition of the fluid phase endocytic process is attributed to the binding of PEG-Chol to the cells' plasma membrane inducing a decrease in surface hydrophobicity of the cells, resulting in a marked decrease in the extent of phagocytic ingestion.

Kinetics of pore formation by an antimicrobial peptide, magainin 2, in phospholipid bilayers

The kinetics of the pore formation by magainin 2, an antimicrobial peptide from Xenopus laevis, in lipid vesicles was investigated. The pore formation was estimated by the efflux of a fluorescent dye, calcein, from large unilamellar vesicles composed of egg yolk phosphatidylglycerol. The time courses of the dye release were well-described by a novel model in which the peptide molecules translocate from the outer to the inner monolayer by forming a pore. The concentration dependence of the leakage rate suggested that the pore consists of pentameric magainin. The obtained kinetic parameters estimate that, at a lipid-to-peptide molar ratio of 117, 9 pores with a lifetime of 40 microseconds open per second per vesicle in the initial phase. The apparent deactivation of the pore with increasing time can be ascribed to the reduced peptide density in the outer leaflet due to the translocation. Incorporation of phosphatidylcholine destabilized the pore, indicating the importance of anionic lipids in the stable pore formation.

Physical-chemistry characteristics and biodistribution of poly(ethylene glycol)-coated liposomes using poly(oxyethylene) cholesteryl ether

Poly(ethylene glycol)-coated liposomes were prepared with poly(oxyethylene) cholesteryl ethers (mPEG-Chol). PEG unit numbers tested were 50, 100 and 200, of which the average molecular weights (m) of PEG were 2200, 4400 and 8800, respectively. Properties of both PEG-coated liposomes and PEG-Chol molecules were investigated. These liposomes exhibited a long circulation time in the blood after i.v. injection in rats, estimated by both the lipid membrane marker, L-alpha-dipalmitoylphosphatidylcholine [2-palmitoyl-9,10-3H](3H-DPPC), and an internal aqueous marker, 3H-inulin. Accumulation in the liver and spleen at 8h-post-injection was significantly reduced compared with conventional liposomes. The percentage of PEG-Chol incorporation in liposomal membranes was also investigated. Liposomes composed of egg yolk phosphatidylcholine (EPC)/PEG-Chol at various molar ratios were separated from free PEG-Chol molecules, which are not incorporated in liposomal membranes by chromatography over Sepharose CL-4B columns, PEG-Chol incorporation reached approx. 14 and 18 mol% of the total lipids with 25% PEG-Chol unit numbers of 200 and 50, respectively. The occupied area per molecule of PEG-Chol was larger than that of Chol, and the fluorescence anisotropy (r) of the initial 25 mol% (8800)PEG-Chol liposomes was smaller than that observed for 12.5 mol% Chol liposomes. PEG-coated liposomes containing calcein were incubated at 37 degrees C in heat-inactivated fetal bovine serum (FBS). In the presence of FBS, calcein leakage was increased with PEG-Chol percentage incorporation and an increase in FBS concentration. The amount released from PEG-coated liposomes represented 60% at maximum and was larger than that of the control liposomes. PEG-Chol molecules are interesting compounds since they can be easily synthesized in a large amount on an industrial scale. The basic physical-chemistry characteristics investigated in this article are critical to assess the pharmacological application of PEG-Chol liposomes as drug delivery systems.

Translocation of a channel-forming antimicrobial peptide, magainin 2, across lipid bilayers by forming a pore

A channel-forming antimicrobial peptide, magainin 2, has been shown to translocate across phospholipid bilayers by forming a pore comprising multimeric peptides. The translocation was demonstrated by four sets of experiments by use of resonance energy transfer from tryptophan introduced into the peptide to a dansyl chromophore incorporated into the lipid membrane. The translocation was coupled to pore formation, as detected by the dye efflux from the lipid vesicles; about 30% of the total peptide molecules translocated into the inner leaflets over 10 min, while 80% of the dye molecules leaked out at a lipid to peptide ratio of 57. This novel model can explain the problems debated so far, i.e., the peptide forms an ion channel whereas the magainin helix essentially lies parallel to the membrane surface. Channel (pore) formation in the vesicles is a transient process observable mainly during the early stage of the peptide membrane interactions.

Morphological differences in the skull of ascorbic acid-deficient ODS rats

The physiological importance of ascorbic acid (AsA) in bone formation has been thought to be due mainly to its effects on collagen production and, consequently, matrix formation. However, effects of AsA deficiency on growing animals are poorly understood. The purpose of this experiment was to find how AsA deficiency affects craniofacial growth cephalometrically, and the periodontal ligament and the bone density of alveolar septum histologically. Five-week-old growing male rats with hereditary defects in AsA synthesis (ODS rats) placed on an AsA-deficient or minimally supplemented diet for 4 weeks showed a marked reduction in plasma AsA level and a negative or slight increment in body weight. Cephalometric evaluation revealed that craniofacial growth was influenced by AsA deficiency. Histological observations of periodontal structure and bone density in AsA-deficient animals showed no difference from controls, whereas the periodontal ligament of the upper first molar in the deficient animals was narrower than that of controls. These observations indicate that AsA deficiency reduces craniofacial size and the width of the periodontal ligament significantly in growing rats, whereas bone density is not affected. Thus, AsA, through collagen production, may be important to the increase in size of the craniofacial structures in growing animals.

Molecular basis for membrane selectivity of an antimicrobial peptide, magainin 2

Magainin peptides, isolated from Xenopus skin, kill bacteria by permeabilizing their cell membranes whereas they do not lyse erythrocytes. To elucidate the rationale for this membrane selectivity, we compared the effects of the membrane lipid composition and the transmembrane potential on the membrane-lytic power of magainin 2 with that of hemolytic melittin. The activity of magainin to zwitterionic phospholipids constituting the erythrocyte surface was extremely weak compared with that of melittin, and acidic phospholipids are necessary for effective action. The presence of sterols reduced the susceptibility of the membrane to magainin. The generation of an inside-negative transmembrane potential enhanced magainin-induced hemolysis. We can conclude that the absence of any acidic phospholipids on the outer monolayer and the abundant presence of cholesterol, combined with the lack of the transmembrane potential, contribute to the protection of erythrocytes from magainin's attack.

Regulation of phospholipase D activity by neutral lipids in egg-yolk phosphatidylcholine small unilamellar vesicles and by calcium ion in aqueous medium

Hydrolysis activity of phospholipase D from Streptomyces chromofuscus (PLD) was studied in small unilamellar vesicles (SUV) of egg yolk phosphatidylcholine (PC). The enzyme was associated with PC-SUV in a Ca(2+)-dependent manner. Both apparent maximum velocity, Vmax(app), and reciprocal of apparent Michaelis constant, i.e., apparent binding constant, 1/Km(app), increased with Ca2+ concentration, and the maximum values of these kinetic parameters were obtained at about 20 microM Ca2+. Incorporation of 1,2-diacylglycerol (DAG), cholesterol (Chol) or alpha-tocopherol (Toc) into PC-SUV induced shift of the antisymmetric PO2- stretching band of PC to lower frequency. The neutral lipids in SUV brought about increase of the Vmax(app) value (Yamamoto et al. (1993) Biochim. Biophys. Acta 1145, 293-297). On the basis of these findings we discussed the regulation of PLD activity in terms of the Ca(2+)-dependent complex formation of PLD with SUV, and the enhancement of susceptibility of the P-O bond in PC molecule by neutral lipids.

Gastric ulcer healing and basic fibroblast growth factor: effects of lansoprazole and famotidine

We examined the effects of lansoprazole and famotidine on gastric basic fibroblast growth factor (bFGF) levels and ulcer healing in patients with gastric ulcer. Sixteen patients with active gastric ulcer were divided into two groups and received treatment with lansoprazole 30 mg/day or famotidine 40 mg/day. They were examined endoscopically at 2, 4, and 8 weeks to measure gastric bFGF levels at the ulcer margin and to assess ulcer healing. Helicobacter pylori infection was determined by a rapid urease test. The two groups were comparable with regard to age, male:female ratio, H. pylori infection rates, and bFGF levels. During treatment, bFGF levels did not change significantly in the famotidine group, whereas they increased by a factor of 2.2 to 2.6 in the lansoprazole group. Cumulative healing rates were also significantly lower in the famotidine group than in the lansoprazole group. These results indicate that lansoprazole increases tissue bFGF levels and promotes gastric ulcer healing in humans.

Posterior bite raising effects on a primary anterior crossbite case

Stainless steel crowns were cemented on the mandibular primary molars to make bite raising for an anterior reversed bite case. Chewing force and MKG were recorded before and after bite raising. Data from MKG revealed that co-ordination pattern of muscle activities after bite raising became higher in masseter muscles than those before anterior reversed bite was corrected easily without any incisal interferences by using this treatment method.

Molecular parameters for the anti-human immunodeficiency virus activity of T22 ([Tyr5,12, Lys7]-polyphemusin II)

T22 ([Tyr5,12, Lys7]-polyphemusin II) was found to exhibit strong anti-human immunodeficiency virus (HIV) activity and exert its effects on a virus-cell fusion process. In the present study, the all-D enantiomer of T22 and its related compounds were synthesized to examine the molecular parameters required for the interaction of T22 with membrane components of cells or viruses in order to exert this anti-HIV activity. The anti-HIV activity of these analogs was investigated in comparison with their membrane permeability with aspect to large unilamellar vesicles (LUVs). The all-D enantiomer of T22 exhibited a 20-fold lower anti-HIV activity compared with T22, whereas they both showed the same membrane permeability. No positive correlation between anti-HIV activity and membrane permeability was observed. These results suggest that the anti-HIV activity of T22 is mediated through the interaction with chiral component(s) of the cell or virus.

Oblique facial cleft, cleft palate, and supernumerary teeth secondary to amniotic bands

A case of oblique facial cleft with supernumerary deciduous molars, probably caused by amniotic bands is reported. Besides facial cleft, and cleft palate and lip, there are sulci on the left side of the face and on the left posterior alveolar ridge. The sulci may be impressions of amniotic bands at a late gestational age and supernumerary teeth may also be related to these amniotic bands.

Effects of cholesterol and cholesteryl oleate on lipolysis and liver uptake of triglyceride/phosphatidylcholine emulsions in rats

Emulsions composed of soy bean triglyceride (TG), egg yolk phosphatidylcholine (PC), cholesterol (Chol) or cholesteryl-oleate (CO), labeled with a cholesteryl ether (3H-CHE) and a triglyceride (14C-TO), were injected into rats. 14C-TO was removed from plasma faster than 3H-CHE. The 14C-labeled moiety is cleaved by digestion of the TG in the emulsion in plasma and is removed to the endothelial cells (lipolysis). In contrast, the 3H-label remains stably associated and represents circulating emulsion particles. The majority (90%) of the 3H-label disappearing from the plasma accumulated in the liver for all types of emulsions. On the basis of these observations, the lipolysis and the removal of emulsion particles to organs (mainly liver) were determined: 30 mole percent of cholesterol (Chol) at the TG-PC emulsion surface markedly retarded organ uptake, but the effect on lipolysis was rather small; 20 mole percent of cholesteryl oleate (CO) in the TG-PC emulsion cores delayed both organ uptake and lipolysis, and induced a rapid increase in organ uptake rate after the initial delay accompanying the gradual progress of lipolysis. Lipolysis led to the enrichment of the cores with CO. Replacement of the core TG by CO, however, induced strong suppression of the liver uptake. These results show that the lipid composition at both surface and core of emulsion particles is a crucial factor in metabolism in the rat.

[A patient with Legionella pneumonia diagnosed early by the PCR method]

A 72-year-old man was admitted to our hospital because of acute respiratory failure. Initially he had been diagnosed as having pneumonia in the lower left lung field and treated with cephem antibiotics by a local physician. Chest X-ray photograph revealed wide-spread infiltrates throughout both lungs, and chest CT scan revealed pleural effusions. The partial pressure of oxygen in arterial blood was 45.8 Torr. In the bronchoalveolar lavage fluid (BALF) specimen, legionella DNA was detected by the polymerase chain reaction (PCR) method. Thus, we were able to diagnose Legionella pneumonia immediately, and to treat the patient successfully.

Study on measurement of delta-aminolevulinic acid in plasma by high-performance liquid chromatography

A method for the determination of delta-aminolevulinic acid in plasma of lead-exposed workers by high-performance liquid chromatography with fluorescence detection of a fluorescent delta-aminolevulinic acid derivative (2-methylidineamino-3,5-diacetyl-4,6-dimethylpropionic acid) was established. The detection limit of delta-aminolevulinic acid in plasma was 0.01 microgram/ml at a signal-to-noise ratio of 5:1. A linear correlation was obtained between the amounts of delta-aminolevulinic acid injected from 0.01 to 0.5 microgram/ml (r = 0.999). The recovery of 0.05 and 0.1 microgram/ml of delta-aminolevulinic acid added to plasma with various concentrations of delta-aminolevulinic acid in plasma ranged from 80.0 to 100.8%. This method, combined with the use of an automatic sampler, should facilitate the routine measurement of delta-aminolevulinic acid in plasma.

Orientational and aggregational states of magainin 2 in phospholipid bilayers

Magainins from Xenopus skin are antimicrobial peptides with broad spectra, and their action mechanisms are considered to be the permeabilization of bacterial membranes. To elucidate their molecular mechanisms, three analog peptides of magainin 2, each having a Trp residue substituted for Phe at the 5th, 12th, or 16th position, were synthesized, and their interactions with acidic phospholipid membranes were investigated by fluorescence. The Trp substitution did not significantly affect the properties of the parent peptide. The binding isotherms of these peptides to the membranes, which were obtained on the basis of fluorescence changes upon membrane binding of the peptides, were sigmoidal, suggesting the association of the bound peptide molecules. A quantitative analysis indicated that the formed aggregate is a dimer. The observation that the initial rate constant of magainin 2 induced leakage of calcein from liposomes was dependent on the fourth power of the peptide concentration demonstrates the formation of a tetrameric pore. A blue shift and intensity enhancement of Trp fluorescence in the presence of the membranes indicate that those Trp residues are buried in the hydrophobic region of the bilayers. Furthermore, the depths of the Trp residues, which were determined using the n-doxylphosphatidylcholine quenching technique, were about 10 A from the bilayer center irrespective of the peptide aggregational state. Thus, it was concluded that the orientation of the magainin 2 alpha-helix is parallel to the membrane surface. A model of the pore formation will be proposed on the basis of these observations.

Role of disulfide linkages in tachyplesin-lipid interactions

In order to elucidate the role of the two disulfide linkages of tachyplesin I (T-SS), a membrane-acting cyclic antimicrobial peptide from Tachypleus tridentatus, we synthesized the acyclic analog (T-Acm) with the four SH groups protected by acetamidomethyl groups and also investigated the interactions of these peptides with lipid bilayers. T-SS induced leakage of calcein from egg yolk L-alpha-phosphatidylglycerol large unilamellar vesicles (PG LUVs) at peptide concentrations 1 order of magnitude smaller than those at which leakage was induced by T-Acm, which coincides with the stronger antimicrobial activities of T-SS. The micellization of PG LUVs was also more efficient for the cyclic peptide. Fluorescence titration studies revealed that binding affinities of both peptides to the PG membranes were similar. Fourier transform infrared polarized attenuated total reflection spectroscopy and fluorescence quenching experiments demonstrated that T-SS and T-Acm both form amphiphilic antiparallel beta-sheet structures in the membranes. They are formed in such a way that the sheet planes lie parallel to the membrane surface with the sheet hydrophobic surfaces penetrating slightly into the hydrophobic region of the bilayers. Furthermore, the observation that the linear T-Acm, the weaker membrane permeabilizer, caused a far more serious membrane disruption suggests the possibility that the mechanisms of membrane permeabilization by the cyclic peptide are different from those by the linear peptide, the latter being the disruption of the lipid organization.

Effects of cholesterol on the miscibility of synthetic glucosamine diesters in lipid bilayers and the entrapment of superoxide dismutase into the positively charged liposomes

Methyl-D-glucosamine-3,6-dilauroyl, dimyristoyl, dipalmitoyl or distearoyl esters were synthesized as positively charged lipids. They were incorporated into phosphatidylcholine liposomal membranes and the entrapment of superoxide dismutase (SOD) into the liposomes was attempted. The efficiency of the SOD-entrapment into the positively charged multilamellar vesicles (MLVs), comprising egg yolk phosphatidylcholine and synthetic glucosamine diesters, was enhanced by the addition of cholesterol to the membranes. A differential scanning calorimetric study showed that the miscibility (solubility) of glucosamine diesters in phosphatidylcholine-bilayers increased on the addition of cholesterol to the membranes. Cholesterol assisted in the mixing of phosphatidylcholines with positively charged glucosamine diesters and increased the positive charges on the liposomal membranes. This was confirmed by incremental increases in the zeta-potential of liposomal membranes with an increase in the cholesterol content. Entrapment of SOD thus became more efficient due to the enhanced electrostatic attraction between the positively charged membranes and the negatively charged SOD, and/or the electrostatic repulsive interactions between positively charged membranes; the latter interactions induced a thickening of the water layer in MLVs.

Eutectic mixed monolayers in equilibrium with phospholipid-bilayers and triolein-liquid phase

Triolein (TO) and phospholipids (egg yolk phosphatidylcholine, egg yolk phosphatidylethanolamine, and bovine brain phosphatidylserine) had low mutual solubilities and separated into the TO-liquid phase and phospholipid-bilayers. Spreading pressures of the TO-phospholipid mixture (i.e., surface pressures of the mixed monolayer in equilibrium with the phase-separating lipid mixture) at the air/saline interface were independent of the lipid composition. On the other hand, collapse pressures of the mixed monolayer of TO and phospholipid (i.e., surface pressures of the mixed monolayer in equilibrium with the TO-liquid phase) at the interface changed with the monolayer composition and were lower than the spreading pressure. The experimental data indicated the spreading and collapse pressures as offering a phase diagram for the presence of equilibrium between the mixed monolayer, the phospholipid-bilayers and the TO-liquid phase. The diagram showed that TO and the phospholipids were miscible in the mixed monolayer, forming an eutectic mixed monolayer. When the mixed monolayer initially had the eutectic composition, no collapse of the monolayer was detected until the surface pressure reached the value of the spreading pressure. No specific complex between TO and the phospholipid is required to explain the stability and collapse of the mixed monolayers. The bulk immiscibility of the lipids elucidated by the spreading pressure-measurements, immediately leads to the phase behaviors observed.