Geodesic surfactant structures.
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Cholesterol↗
Biomedical subjects
B Sternberg
Publications and source records attributed to B Sternberg.
New structures in complex formation between DNA and cationic liposomes visualized by freeze-fracture electron microscopy.
Structures formed during interaction of cationic liposomes and plasmid DNA were studied by freeze-fracture electron microscopy and their morphology was found to be dependent on incubation time and DNA concentration. These structures were formed with liposomes composed of DC-Chol and DOPE after 30 min incubation at DNA:lipid concentrations encompassing maximal transfection activity. They resembled liposome complexes (meatballs) and additionally bilayer-covered DNA tubules (spaghetti), whereby the DNA-tubules were found to be connected to the liposome complexes as well as occurring free in the suspension. At later times and higher DNA-to-liposome ratios the complexes grow larger while their membranes become discontinuous, allowing the self-encapsulation of the DNA. The relative transfection potency of the various morphologically distinct structures is discussed.
Avian Sarcoma Viruses↗
Incorporation of vitamin D3-derivatives in liposomes of different lipid types.
Vitamin D3-derivatives are known to be effective in differentiation and proliferation of epidermal cells. However, under certain circumstances, they also may show a hypercalcamic activity which can be a serious limitation in their use for dermatological application. For keeping small the negative side effects of vitamin D3-derivatives and for increasing the drug concentration in the skin we investigated their incorporation in liposomes to optimize their use for psoriasis treatment. The incorporation of vitamin D3-derivatives in liposomes of different lipid composition was studied by HPLC, DSC and freeze-fracture electron microscopy. Incorporation rates of more than 80% of the offered drug were found with significant variations related to the number of hydroxyl-groups in the A-ring, opened or closed B-ring, and some modifications in the side chain of the steroid-molecules. In general, the incorporation rates in egg-PC liposomes have been of about 3% up to 10% higher than in DMPC liposomes. Results, obtained by DSC and freeze-fracture electron microscopy, show a depression of the phase transition of DMPC bilayers by incorporation of vitamin D3 already at a concentration of 10 mol%. These results support the idea that vitamin D3 and its analoga investigated are incorporated into the lipid bilayer modifying there the lipid-lipid interactions.
Calorimetry, Differential Scanning↗
Interaction of liposomal incorporated vitamin D3-analogues and human keratinocytes.
The influence of different liposomal qualities, loaded with a variety of vitamin D3-analogues, on the proliferation and interleucine 1 alpha-release (IL-1 alpha) of human keratinocytes was examined by fluorimetric and colorimetric measurements to optimize their use for psoriasis treatment. In comparison, the effects of the free drugs, as 25-hydroxyvitamin D3, calcipotriol, and calcitriol, as well as of empty liposomes have been studied. At the interaction between empty liposomes (< 200 nm) and HaCaT-cells has been looked by electron microscopy. Empty liposomes, made of DMPC as well as of egg-PC, can be used as drug carrier without any inhibiting effect on the proliferation of human keratinocytes at lipid concentrations of < 10(-4) M. Under the influence of the free drugs investigated an inhibition of cell growth as well as of the IL 1 alpha-release was measured at drug concentrations of > or = 10(-8) M. In comparison the related liposomal drug formulations didn't show any diminishing in the proliferation effects caused by the free drugs. A significant improvement, however, was only found in the action of DMPC-incorporated 25-hydroxyvitamin D3 at drug concentration of 10(-7) M. These results suggest that there is no remarkable improvement in the action of liposomal incorporated vitamin D3-analogues neither related to their proliferation nor their IL1 alpha-releasing effects. The influence of liposomal incorporated vitamin D3-analogues in keeping small their negative side effects has to be investigated at a more relevant model.
Cell Division↗
[Liposomes in medicine. An assessment of current status].
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Drug Administration Routes↗
In-vitro stability and cytostatic activity of liposomal formulations of 5-fluoro-2'-deoxyuridine and its diacylated derivatives.
The water-soluble antineoplastic agent 5-fluoro-2'-deoxyuridine (FUdR) was encapsulated in the water phase of liposomes of different lipid compositions. The retention of this drug upon storage and during contact with plasma was assessed. It was found that, upon refrigeration, diffusion of FUdR across the liposome bilayer was considerably faster when the drug was encapsulated in fluid-type liposomes (egg PC/PS/CHOL) than in solid-type liposomes (DSPC/DPPG/CHOL). With either composition, leakage of the drug from the liposomes was accelerated upon contact with plasma. To achieve improved liposomal retention of the drug, FUdR was converted to a lipophilic prodrug by esterifying the free hydroxyl groups in the deoxyribose moiety with fatty acids of different chain lengths. Thus FUdR-dipalmitate (C-16) and FUdR-dioctanoate (C-8) were synthesized and incorporated in liposomes. The dipalmitoyl derivative could be incorporated upto 13 mol% in solid-type liposomes but to only 2 mol% in fluid-type liposomes. Freeze-fracture electron microscopy revealed no major differences between control liposomes and those containing the prodrug. FUdR-dipalmitate was found to be firmly associated with the liposomal bilayer in both liposome-types: no exchange of the pro-drug with blood constituents or hydrolysis by serum esterases could be registered when the liposomes were incubated with serum. On the other hand, liposome-incorporated FUdR-dioctanoate was found to be readily extracted from the liposomes by serum components (predominantly albumin) and was found to be degraded rapidly by serum esterase activity. The antitumor activity of FUdR-prodrugs was determined using C26 colon adenocarcinoma cells. This cell line was found to be highly sensitive to FUdR. Liposomal FUdR-dioctanoate inhibited cell growth in the same concentration range as unesterified FUdR. FUdR-dipalmitate, however, was more than two orders of magnitude less potent in inhibiting cell proliferation. Its antiproliferative activity was dependent on the liposome-type used: when incorporated in fluid-type liposomes, antiproliferative activity of FUdR-dipalmitate was several-fold higher than in solid-type liposomes. The difference in antitumor activity between FUdR-dipalmitate and FUdR-dioctanoate and between FUdR-dipalmitate in the fluid- and solid-type liposomes could be explained by differences in the rate of hydrolysis of the prodrugs to FUdR by esterase activity in the tumor cells or in the growth medium.
Antineoplastic Agents↗
Coupling of ligands to liposomes independently of solute entrapment: observations on the formed vesicles.
Bovine serum albumin (BSA), employed as a model ligand, was covalently linked (about 16% of the amount used) to small unilamellar vesicles (SUV) composed of phospholipid, cholesterol and N-(p-aminophenyl)stearylamide (APSA) (molar ratios 1:1:0.05). SUV with bound BSA were then used to generate dehydration-rehydration vesicles (DRV) in the presence of tetanus toxoid and/or carboxyfluorescein (CF). Nearly all of the SUV-bound BSA (about 15% of the original amount) was recovered in the multilamellar DRV formed, with a considerable proportion (42-62%) of the ligand becoming available on the outer bilayers. This apparent spatial reorientation of BSA within DRV also caused the entrapped toxoid to shift to some extent to the liposomal surface. There was no significant difference in the z average mean size between DRV with and without coupled BSA (543 and 555 nm diameter, respectively). Percent number diameter distribution data revealed that 71.2 (BSA-free) and 76.4% (BSA-containing DRV) of the vesicles had diameters of about 300-440 and 330-420 nm, respectively. However, in terms of percent mass diameter distribution, 69.5% (BSA-free) and 65.2% (BSA-containing DRV) of the mass was in vesicles with corresponding ranges of diameter of 1381-2975 and 1086-2840 nm. Vesicle size heterogeneity in both preparations was confirmed by freeze-fracture electron microscopy which also indicated that structures with or without bound BSA, were mostly vesicular of the multilamellar type. Judging from CF latency values, ligand-bearing DRV were stable on incubation with blood plasma at 37 degrees C for 24 h. Stability was, however, reduced significantly when the amount of ligand bound was excessive. The present approach allows for the coupling of ligands to and the entrapment of antigens and other labile solutes in liposomes independently, thus avoiding potential damage of such solutes by the coupling reagents.
Cholesterol↗
The essential role of specific Halobacterium halobium polar lipids in 2D-array formation of bacteriorhodopsin.
The mechanism whereby bacteriorhodopsin (BR), the light driven proton pump from the purple membrane of Halobacterium halobium, arranges in a 2D-hexagonal array, has been studied in bilayers containing the protein, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and various fractions of H. halobium membrane lipids, by freeze fracture electron microscopy and examination of optical diffractograms of the micrographs obtained. Electron micrographs of BR/DMPC complexes containing the entire polar lipid component of H. halobium cell membranes or the total lipid component of the purple membrane, with a protein-to-total lipid molar ratio of less than 1:50 and to which 4 M NaCl had been added, revealed that trimers of BR formed into an hexagonal 2D-array similar to that found in the native purple membrane, suggesting that one or more types of the purple membrane polar lipids are required for array formation. To support this suggestion, bacteriorhodopsin was purified free of endogenous purple membrane lipids and reconstituted into lipid bilayer complexes by detergent dialysis. The lipids used to form these complexes are 1,2-dimyristoyl-sn-glycerol-phosphocholine (DMPC) as the major lipid and, separately, each of the individual lipid types from the H. halobium cell membranes, namely 2,3-di-O-phytanyl-sn-glycero-1-phosphoryl-3'-sn-glycerol 1'-phosphate (DPhPGP), 2,3-di-O-phytanyl-sn-glycero-1-phosphoryl-3'-sn-glycerol 1'-sulphate (DPhPGS), 2,3-di-O-phytanyl-sn-glycero-1-phosphoryl-3'-sn-glycerol (DPhPG) and 2,3-di-O-phytanyl-1-O-[beta-D-Galp-3-sulphate-(1----6)-alpha-D- Manp-(1----2)-alpha-D-Glcp]-sn-glycerol (DPhGLS). When examined by freeze-fracture electron microscopy, only the complexes containing 2,3-di-O-phytanyl-sn-glycero-1-phosphoryl-3'-sn-glycerol- 1'-phosphate or 2,3-di-O-phytanyl-sn-glycero-1-phosphoryl-3'-sn-glycerol-1'-sulphate, at high protein density (less than 1:50, bacteriorhodopsin/phospholipid, molar ratio) and to which 4 M NaCl had been added, showed well defined 2D hexagonal arrays of bacteriorhodopsin trimers similar to those observed in the purple membrane of H. halobium.
Bacteriorhodopsins↗
Carboxyacyl derivatives of cardiolipin as four-tailed hydrophobic anchors for the covalent coupling of hydrophilic proteins to liposomes.
Two carboxyacyl derivatives of cardiolipin, O-succinyl- and O-glutarylcardiolipin, were synthesized with the aim of using them as artificial membrane anchors for the immobilization of hydrophilic proteins to liposomes. Four adjacent fatty acid residues can be introduced into a protein with only one single amino group being blocked, by reacting the cardiolipin derivatives with the protein amino groups after carbodiimide activation. alpha-Chymotrypsin, used as a model protein, and modified with on average two molecules of O-succinylcardiolipin was incorporated into liposomes, which had been prepared by different methods, with very high yield. If incorporated in preformed liposomes, the carboxyacyl cardiolipin anchors were also efficient in binding proteins to liposomal surfaces. Up to 350 micrograms chymotrypsin/mumol lipid were coupled to small unilamellar vesicles, preserving reactivity of the enzyme towards specific macromolecular inhibitors. Human IgG could also be bound to anchor-containing liposomes with high protein to lipid coupling ratio as well as high coupling yield.
Acylation↗
Reversible disc-micellization of dimyristoylphosphatidylcholine bilayers induced by melittin and [Ala-14]melittin.
The properties of melittin and a synthetic analogue, [Ala-14]melittin (P14A), in inducing reversible transitions between vesicles and micelles at the liquid-crystalline to gel phase transition temperature (Tm) in complexes with saturated phosphatidylcholines has been studied by deuterium NMR and freeze-fracture electron microscopy (EM). At concentrations between 3 and 5 mol% relative to lipid, each peptide causes reversible micellization of dimyristoylphosphatidylcholine (DMPC) bilayers when the temperature is lowered below Tm. At concentrations of 5 mol% relative to lipid, the peptides induce macroscopic magnetic orientation of DMPC bilayers at temperatures around the centre of the lipid phase transition; at temperatures a few degrees above Tm, magnetic orientation is lost. These effects suggest a progressive phase separation of peptide and lipid on cooling the complexes through the phase transition, resulting in increased vesicle deformability. The rates of gel phase micellization, and of bilayer reformation from micelles at temperatures above Tm, are decreased by 100-fold in P14A:DMPC complexes compared with melittin: DMPC complexes. Freeze-fracture EM indicates that P14A suppresses the formation of the gel phase in DMPC bilayers at temperatures below Tm. EM observations of the time-dependence of the reformation of bilayers from micelles after incubating P14A:DMPC micellar complexes at temperatures above Tm indicate that micelles fuse to form growing bilayer sheets from which multilamellar vesicles eventually form. The presence of intramembranous particles (IP) on the fracture faces of both melittin: DMPC complexes and P14A:DMPC complexes in the fluid phase indicates that under the conditions of the study (50 mM Tris-HCl (pH 7.5), 5 mM EDTA) the peptides are organized as discrete aggregates that penetrate deeply into the bilayer.
Deuterium↗
Identification of trapped and boundary lipid binding sites in M13 coat protein/lipid complexes by deuterium NMR spectroscopy.
The major coat protein of M13 bacteriophage has been incorporated into bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine, deuterated in the trimethyl segments of the choline headgroup (DMPC-d9). Two-component deuterium and phosphorus-31 NMR spectra have been observed from bilayer complexes containing the coat protein, indicating slow exchange (on the deuterium quadrupole anisotropy and phosphorus-31 chemical shift averaging time scales) of lipid molecules of less than 10(3) Hz between two motionally distinct environments in the complexes. The fraction of the isotropic spectral component increases with increasing M13 protein concentration, and this component is attributed to lipid headgroups, which are disordered relative to their order in protein-free bilayers. The activation energy of the fast local motions of the trimethyl groups of the choline residue in the headgroup decreases from 23 kJ mol-1 in the pure lipid bilayers to 20 kJ mol-1 for the protein-associated lipid headgroups. The chemical exchange rate of lipid molecules between the two motionally distinct environments has been estimated to be 20-50 Hz by steady-state line-shape simulations of the deuterium spectra of DMPC-d9/M13 coat protein complexes using exchange-coupled modified Bloch equations. The off-rate was, as expected from one-to-one exchange, independent of the L/P ratio; tau off -1 = 0.23 kHz. It is suggested that the protein-associated lipid may be trapped between closely packed parallel aggregates of M13 coat protein and that the high local concentration of protein in a one-dimensional arrangement in lipid bilayers may be required for the fast reassembly of phage particles before release from an infected cell.
Bacteriophages↗
Electron microscopic and biophysical studies of liposome membrane structures to characterize similar features of the membranes of Streptomyces hygroscopicus.
To characterize the novel non-planar plasma membrane structure of bacteria (wafer structure), liposome membranes from the bacterial lipid mixture and individual lipid fractions were prepared and investigated by freeze-fracture electron microscopy, microcalorimetry and 31P-NMR spectroscopy. The phospholipid content of the membranes is essential for the formation of the non-planar membrane structure and there is no indication that the formation of the structure is connected with temperature-induced lipid phase transition processes. An exaggerated form of the wafer structure (raspberry structure) is also visible and additionally, in both cases, many small spherical vesicles are observed. We suggest that both membrane features of the liposomal and bacterial membranes are induced by these vesicles, forming a hexagonal or cubic organization of vesicles on the cytoplasmic surface of the biological membrane, and in between the multilamellae in the artificial membranes.
Calorimetry↗
[Brain abscess in the newborn infant (27 cases: initial electroclinical study, course].
The authors studied 27 brain abscesses in neonates. The neonates were divided in two groups: neonates with seizures and neonates without seizures. The authors tested the diagnostic and predictive value of the initial EEG aspect. They noted the absence of correlation between EEG focal abnormalities and localizations shown by the CT scan. They observed a severe electroclinical evolution in more than fifty percent of the cases presented.
Brain Abscess↗
[Medical behavior and sudden infant death].
The authors recall some hypothesis about factors of risk which are acknowledged as possible element of SIDS and may receive a treatment: gastroesophageal reflux, vagal hyperexcitability and enzymatic deficit.
France↗
Respiratory pauses and periodic breathing assessed by cardio-pneumography in normal infants and in SIDS siblings.
450 cardio-pneumograms (CPG) were performed on two successive nights in 68 controls and 235 SIDS siblings. The number of respiratory pauses greater than or equal to 5 sec and greater than or equal to 10 sec (NP) and the time of periodic breathing (PB) were calculated per 100 minutes of recording. Recordings were arranged into five age groups corresponding to the 1st, 2nd, 3rd, 4th and 5th-6th month of life. No significant differences in NP and PB were found when controls and SIDS siblings were compared separately within each age group, neither as a function of gestational age (less than 40 weeks GA vs greater than or equal to 40 weeks GA), nor as a function of the results of the 1st vs the 2nd night of recording. Nor was any significant difference in NP and PB found when comparing control vs sibling babies within each age group for the 1st or for the 2nd night of recording. In SIDS siblings, there was a significant decrease in the three variables studied between the 1st and the 2nd month of life. No significant decrease was found in controls. We conclude that SIDS siblings are not different from controls of the same age when respiratory variables are studied by CPG recordings.
Child, Preschool↗
Are polygraphic and cardiopneumographic respiratory patterns useful tools for predicting the risk for sudden infant death syndrome? A 10-year study.
Between 1974 and 1984 we have studied 204 control infants (C) comparing them with 650 SIDS siblings (SS) and 146 near-miss for SIDS (NM). These 1,000 full-term infants were recorded by day polysomnography (DPSG; n = 417), night polysomnography (NPSG; n = 257) and cardiopneumography (CPG; n = 2,600). Records were visually analyzed. In DPSG and NPSG, total amount of central, mixed and obstructive apnea as well as the percentage of periodic breathing was studied in each sleep state (active sleep, AS; quiet sleep, QS; indeterminate sleep, IS, and total sleep, TS) and over the total recording time (TRT). In CPG, only the total amount of central apnea and percentage of periodic breathing over TRT were studied. Infants were grouped according to postnatal age: less than 5, greater than or equal to 5 to less than or equal to 13, and greater than 13 to less than or equal to 26 weeks. In each age group results were compared as follows: C vs. SS, C vs. NM, and SS vs. NM for each parameter studied. Before 5 weeks and after 13 weeks there was no significant difference between C and SS, C and NM, and SS and NM in DPSG and NPSG for all categories of central, mixed and obstructive apnea as well as the percentage of periodic breathing in different sleep states and over TRT. Similar results were obtained in CPG for all categories of central apnea and percentage of periodic breathing over TRT.(ABSTRACT TRUNCATED AT 250 WORDS)
Age Factors↗
Structures of liposome membranes as models for similar features of cytoplasmic membranes of bacteria.
To characterize a special kind of membrane structure, visible in the cytoplasmic membranes of a Streptomyces hygroscopicus strain, liposome membranes were prepared from their extracted lipid mixture and from their lipid fractions (phospholipids, glycolipids, neutral lipids) and investigated by freeze-fracture electron microscopy. Liposome membranes made of the extracted lipid mixture reveal this special membrane structure, named wafer structure, from its regular pattern of bulges (30-40 nm in diameter). That is the proof that this membrane feature is a lipid structure. Liposome membranes prepared from the lipid fractions show the wafer structure if they are made of the phospholipid fraction only or in combination of this fraction with one or both of the other lipid fractions, indicating that wafer structure formation is primarily connected with the phospholipid content of the membranes. The glycolipid- and neutral lipid fractions amplify this phospholipid structure only. Additional to the wafer structure a raspberry structure with bulges of 55-65 nm in diameter is visible in some case. Obviously both structures are related.
Cell Membrane↗