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At least 703 records · Page 39Linked to original sources
PubMed2001

Tamoxifen perturbs lipid bilayer order and permeability: comparison of DSC, fluorescence anisotropy, laurdan generalized polarization and carboxyfluorescein leakage studies.

The perturbation of the lipid bilayer structure by tamoxifen may contribute to its multiple mechanisms of anticancer action not related to estrogen receptors. This study evaluates the effect of tamoxifen on structural characteristics of model membranes using differential scanning calorimetry (DSC), fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-[4-[trimethylammonium)phenyl]-6-phenylhexa-1,3,5-triene (TMA-DPH), as well as 6-dodecanoyl-2-dimethylaminonaphthalene (Laurdan) generalized polarization. The comparative measurements in multilammelar vesicles (MLV) prepared from dipalmitoylphosphatidylcholine (DPPC) revealed that tamoxifen decreases the phase transition temperature (Tm) paralleled by a broadening of the phase transition profile. In large unilamellar vesicles (LUV) prepared from egg yolk phosphatidylcholine (EPC), tamoxifen increased the lipid bilayer order predominantly in the outer bilayer region. From membrane permeability measurements, we conclude that the tamoxifen-induced release of entrapped carboxyfluorescein (CF) results from a permanent bilayer disruption and the formation of transient holes in the lipid bilayer.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1999

Gangliosides asymmetrically alter the membrane order in cultured PC-12 cells.

Exogenous gangliosides readily associate with the cell membranes and produce marked effects on cell growth and differentiation. We have studied the effect of bovine brain gangliosides (BBG) on the membrane dynamics of intact cells. The structural and dynamic changes in the cell membrane were monitored by the fluorescence probes DPH, TMA-DPH and laurdan. Incorporation of BBG into the cell membrane decreased the fluorescence intensity, lifetime and the steady state anisotropy of TMA-DPH. Analysis of the time resolved anisotropy decay by wobbling in the cone model revealed that BBG decreased the order parameter, and increased the cone angle without altering the rotational relaxation rate. The fluorescence intensity and lifetime of DPH were unaffected by BBG incorporation, however, a modest increase was observed in the steady state anisotropy. BBG incorporation reduced the total fluorescence intensity of laurdan with pronounced quenching of the 440-nm band. The wavelength sensitivity of generalized polarization of laurdan manifested an ordered liquid crystalline environment of the probe in the cell membrane. BBG incorporation reduced the GP values and augmented the liquid crystalline behavior of the cell membrane. BBG incorporation also influenced the permeability of cell membranes to cations. An influx of Na+ and Ca2+ and an efflux of K+ was observed. The data demonstrate that incorporation of gangliosides into the cell membrane substantially enhances the disorder and hydration of the lipid bilayer region near the exoplasmic surface. The inner core region near the center of the bilayer becomes slightly more ordered and remains highly hydrophobic. Such changes in the structure and dynamics of the membrane could play an important role in modulation of transmembrane signaling events by the gangliosides.

2-Naphthylamine↗
PubMed2001

pH-sensitive nanoparticles of poly(amino acid) dodecanoate complexes.

Nanoparticles were formed by the complexation of poly(L-arginine) (PLA), poly(L-histidine) (PLH) and poly(L-lysine) (PLL) with dodecanoic acid (C12). Dynamic light scattering, zeta potential measurements, atomic force microscopy, fluorescence, and circular dichroism spectroscopy were used for their characterization. It was found that the diameters of the poly(L-arginine) dodecanoate (PLA-C12), poly(L-histidine) dodecanoate (PLH-C12), and poly(L-lysine) dodecanoate (PLL-C12) complex nanoparticles were in the range 120-200 nm. Furthermore, the pH-sensitive dissolution and the surface charges can be adjusted by choosing PLA, PLH and PLL. The particle stability against basic pH values increases with increasing pK(a) value of the poly(amino acid) in the series PLH-C12, PLL-C12 and PLA-C12. The particles as such show a core-shell morphology. Their cores are formed by stoichiometric poly(amino acid) dodecanoate complexes while the shells stabilizing the particles are formed by cationic poly(amino acid) chains in an uncomplexed state. The particles were tested as containers for hydrophobic molecules such as pyrene, which served as a fluorescence probe for measuring the polarity within the particles, and Q(10) which functioned as a model drug. The maximum uptake of Q(10) into the nanoparticles is about 13% (w/w), thereby making the complexes attractive as simple drug carriers for controlled release purposes. Circular dichroism measurements revealed that the poly(amino acid) chains of PLA-C12 and PLL-C12 adopt predominantly an alpha-helix and that of PLH-C12 a beta-sheet.

Circular Dichroism↗
PubMed2003

Brain delivery of vasoactive intestinal peptide (VIP) following nasal administration to rats.

The aim of this work was to study in rats the nasal route for the brain delivery of the vasoactive intestinal peptide (VIP) neuropeptide. After evaluating VIP stability in solutions obtained from nasal washes, the effect of formulation parameters (pH 4-9, 0-1% (w/v) lauroylcarnitine (LC), hypo- or isoosmolality) on the brain uptake of intranasally administered VIP (10(-8)M)/125I-VIP (300,000 cpm/ml) was studied, using an in situ perfusion technique. Brain radioactivity distribution was assessed by quantitative autoradiographic analysis. Results were compared to intravenously administered VIP. With a hypotonic formulation at pH 4 containing 0.1% LC and 1% bovine serum albumin, VIP stability was satisfactory and loss by adsorption was minimal. Using this formulation, around 0.11% of initial radioactivity was found in the brain after 30 min perfusion and was located in the olfactory bulbs, the midbrain and the cerebellum. HPLC analysis of brain and blood extracts demonstrated the presence of intact VIP in brain and its complete degradation in the blood compartment. By intravenous administration, no intact VIP was found either in brain or in blood. In conclusion, intact VIP could be delivered successfully to the brain using the intranasal route for administration.

Administration, Intranasal↗
PubMed2005

[Spontaneous skin necrosis from acquired protein S deficiency in a renal transplant recipient].

INTRODUCTION: Spontaneous skin necrosis revealed acquired protein S deficiency due to isotype G autoantibodies. CASE: This 31-year-old male renal transplant recipient, receiving immunosuppressive treatment, was hospitalized for necrotic purpural lesions. We were not able to detect any triggering factor. Sustained anticoagulant therapy remained essential to prevent new skin lesions and perhaps more thrombotic events. COMMENTS: This condition is rare in adulthood, but is well described in children's purpura fulminans, especially the post-varicella form. Its mechanism remains unclear.

Adult↗
PubMed2001

Loss of apoB-100 secondary structure and conformation in hydroperoxide rich, electronegative LDL(-).

A subpopulation of low-density lipoproteins (LDL) is present in human plasma that contains lipid hydroperoxides and is more negatively charged (LDL(-)) than normal native LDL. By circular dichroism and tryptophan lifetime measurements we found that apoB-100 secondary structure is markedly decreased and its conformation is severely altered in LDL(-). The low tryptophan fluorescence intensity confirms the oxidative degradation of the lipoprotein, and the very long lifetime value of one of its decay components indicates a low polarity environment for the remaining unbleached residues. Either a peculiar folding or, most likely, a sinking of the apoB-100 into the lipid core can account for the observed long lifetime component. Oxidation in vitro produces a similar unfolding of the apolipoprotein but the lifetime of tryptophan fluorescence is shifted to lower values, indicating that the denatured apoprotein remains at the hydrophilic surface of the lipoprotein particle. A disordering and an increased polarity of the LDL(-) surface lipids was demonstrated by measuring the generalized polarization of 2-dimethylamino-6-lauroylnaphthalene (Laurdan). The looser monolayer packing apparently favors the new conformation of apoB-100 and its sinking into a more hydrophobic environment, possibly accounting for it reduced receptor binding properties.

2-Naphthylamine↗
PubMed2003

In vivo CH3(CH2)11SAu SAM electrodes in the beating heart: in situ analytical studies relevant to pacemakers and interstitial biosensors.

To study in vivo modification of the SAM equivalent circuit when a highly ordered SAM is used as a bioelectrode, dodecanethiolate SAM-Au intramuscular electrodes were studied in living rat heart in a challenging in situ perfused rat model by impedance spectroscopy, cyclic voltammetry, and neutron activation analysis (NAA). The SAM layer experienced disintegration in vivo biological system, as NAA detected the presence of Au atoms that had leached into the surrounding living tissue. Therefore, the underlying Au surface became exposed during biological implant. Study by impedance spectroscopy, however, revealed perfect capacitive behavior for the SAM, similar to in vitro behavior. Electrodes showed a pure capacitive Nyquist plot with 86.1-89.4 degrees near-vertical line segments as the equivalent circuit locus, as for a parallel plate capacitor. Impedance magnitude varied linearly with 1/omega excluding diffusionally limited ionic charge transport. There was no diffusional conductive element Z(W infinity ) or spatially confined Warburg impedance Z(D). The effect of in vivo exposure of a highly ordered SAM is a 'sealing over' effect of new defects by the binding of proteinaceous or lipid species in the biological milieu, a fact of significance for SAM electrodes used either as pacemaker electrodes or as a platform for in vivo biosensors.

Animals↗
PubMed1999

Myristic acid analogs are inhibitors of Junin virus replication.

The effects of two myristic acid analogs on Junin virus (JV) replication were investigated. The compounds chosen for the study were DL-2-hydroxymyristic acid (2OHM), an inhibitor of N-myristoyltransferase (NMT), which binds the enzyme and blocks protein myristoylation, and 13-oxamyristic acid (13OM), a competitive inhibitor of NMT which incorporates into the protein instead of myristic acid. Both types of analogs achieved dose-dependent inhibition of viral multiplication at concentrations not affecting cell viability. The 50% inhibitory concentration values determined by a virus-yield inhibition assay for different strains of JV, including a human pathogenic strain, and for the related arenavirus, Tacaribe, were in the range 1.6 to 20.1 microM, with 13OM as the most active compound. From time of addition and removal experiments, it can be concluded that both analogs inhibit a late stage in the JV replicative cycle, and their effect was partially reversible. The cytoplasmic and surface expression of JV glycoproteins was not affected in the presence of the compounds, as revealed by immunofluorescence staining, suggesting that JV glycoprotein myristoylation would not be essential for the intracellular transport of the envelope proteins, but it may have an important role in their interaction with the plasma membrane during virus budding.

Acyltransferases↗
PubMed2000

Infrared intensity of 1-monolaurin-water systems in the gel phase.

The infrared spectra of 1-monolaurin-water systems, where KSCN is added as the intensity standard, were observed and the infrared intensity of the bands due to acyl groups measured relatively to that of the CN stretching. The infrared intensities of the bands parallel and perpendicular to the paraffin chains decrease and increase, respectively, on going from the crystalline 1 phase to the gel phase, confirming that these intensity changes result from the long-range interaction among oscillating dipoles. The infrared spectra with no CH2 rocking and the splitting of the CH2 rocking are also discussed with the same interaction model.

Gels↗
PubMed2000

Infrared intensity and morphology of l-monolaurin-water systems.

The infrared spectra for some metastable states in 1-monolaurin water systems were observed at room temperature, where the relative intensity of bands due to paraffin chains changed considerably, especially in the CH2 rockings, which disappear in some cases. It is considered that the spectral changes result from the morphology change on going from the crystal to the liquid crystal, smectic B phase, so-called gel phase, which consists of the lipid bilayers with ordered paraffin chains alternating with water layers. The model for explaining the intensity change is proposed on the basis of the interaction among oscillating dipoles.

Glycerides↗
PubMed1995

Insulin receptor autophosphorylation and signaling is altered by modulation of membrane physical properties.

Many membrane functions are modulated by the bulk biophysical properties of the membrane. Various compounds which alter membrane physical properties were investigated for their ability to modulate insulin receptor autophosphorylation and signaling. Compounds which raise the bilayer to hexagonal phase transition temperature in model membranes, including carbobenzoxydipeptides, apolipoprotein A-I, acyl carnitines, and lysophosphatidylcholine, inhibited insulin stimulation of insulin receptor tyrosine phosphorylation of isolated receptors as well as in cells overexpressing human insulin receptor. For compounds of similar structure, the inhibition of insulin receptor tyrosine phosphorylation correlates well with their bilayer-stabilizing potency. Most of the compounds which inhibit tyrosine phosphorylation of the insulin receptor also inhibited glucose uptake in the same cells. Compounds which lower the bilayer to hexagonal phase transition temperature in model membranes enhanced insulin stimulation of autophosphorylation in isolated receptors, with no effect on insulin receptor activity in NIH 3T3 HIR 3.5 cells. The effects of cationic amphiphiles were not readily predictable from their membrane modulating activity. All of the compounds tested exert their effects independent of changes in insulin binding to the receptor or changes in the basal tyrosine kinase activity of the receptor. This provides evidence that mechanism of modulation of insulin signaling by these additives lies in their ability to alter the bulk physical properties of the membrane. The results suggest that membrane monolayer curvature strain is a factor contributing to the efficiency of insulin signal transduction.

3T3 Cells↗
PubMed2000

Estradiol enhances the resistance of LDL to oxidation by stabilizing apoB-100 conformation.

Among different proposed mechanisms to account for the protection exerted by estrogens against cardiovascular diseases, the antioxidant effect has attracted considerable attention. We confirmed that 17-beta-estradiol (E2), when added to human LDL at a 6:1 ratio to apoB-100, markedly delays the phase of massive LDL lipid peroxidation induced by Cu(2+). We also observed an increased oxidative resistance of E2-treated LDL by monitoring the early phase of oxidative degradation on the basis of increased LDL surface polarity by the generalized polarization of the lipophilic fluorescent probe 2-(dimethylamino)-6-lauroylnaphthalene (Laurdan). A scavenging of free radicals by E2 is ruled out since, consistent with its structure, its rate constant for the reduction of peroxy radicals is extremely low, i.e., 0.02% of that of vitamin E. Tryptophan fluorescence lifetime and circular dichroism measurements revealed that (i) apoB-100 undergoes a conformational modification and a progressive loss of secondary structure during lipid peroxidation; (ii) E2 increases apoB-100 secondary structure and modifies its conformation; and (iii) the apoB-100 conformational change induced by E2 makes this protein resistant to modifications brought about by lipid peroxidation. We propose that E2, by affecting apoB-100 secondary structure and conformation, modifies the interaction of this protein with the outer layer of the LDL particle thus increasing its overall oxidative resistance.

2-Naphthylamine↗
PubMed2001

Mitochondrial creatine kinase binding to phospholipids decreases fluidity of membranes and promotes new lipid-induced beta structures as monitored by red edge excitation shift, laurdan fluorescence, and FTIR.

Structural modifications induced by the binding of mitochondrial creatine kinase (mtCK) to saturated and unsaturated phospholipids were monitored by using Laurdan, a membrane probe sensitive to the polarity of the environment. The abrupt change characteristic of a phase transition of lipids alone was attenuated by addition of mtCK. Generalized polarization spectra indicated that mtCK surface binding changed the phospholipid liquid-crystalline state to a more rigid state. Infrared spectra of lipids further strengthened these results: upon mtCK binding, the phospholipid methylene chains had a more rigid conformation than that observed without mtCK at the same temperature. After mtCK binding to vesicles of perdeuterated dimyristoylphosphatidylcholine and nondeuterated dimyristoylphosphatidylglycerol, no lateral phase separation was observed, suggesting that both lipids were rigidified. Moreover, mtCK bound to liposomes exhibited an uncommon red edge excitation shift of 19 nm, while that of the soluble enzyme was only 6 nm. These results indicated that the environment of some mtCK tryptophan residues was motionally restricted. Strong stabilization of the enzyme structure against heat denaturation was observed upon lipid binding. In addition, lipids promoted a new reversible protein-protein or protein-lipid interaction, as evidenced by infrared data showing a slight modification of the beta sheet over alpha helix ratio with formation of a new 1632-cm(-)(1) beta sheet instead of the soluble protein 1636-cm(-)(1) one. Such modifications, inducing a decrease in the fluidity of the mitochondrial membranes, may play a role in vesicle aggregation; they could be implicated in the appearance of contact sites between internal and external mitochondrial membranes.

2-Naphthylamine↗
PubMed1990

12-[(5-iodo-4-azido-2-hydroxybenzoyl)amino]dodecanoic acid: biological recognition by cholesterol esterase and acyl-CoA:cholesterol O-acyltransferase.

Potential probes of protein cholesterol and fatty acid binding sites, namely, 12-[(5-iodo-4-azido-2-hydroxybenzoyl)amino]dodecanoate (IFA) and its coenzyme A (IFA:CoA) and cholesteryl (IFA:CEA) esters, were synthesized. These radioactive, photoreactive lipid analogues were recognized as substrates and inhibitors of acyl-CoA:cholesterol O-acyltransferase (ACAT) and cholesterol esterase, neutral lipid binding enzymes which are key elements in the regulation of cellular cholesterol metabolism. In the dark, IFA reversibly inhibited cholesteryl [14C]oleate hydrolysis by purified bovine pancreatic cholesterol esterase with an apparent Ki of 150 microM. Cholesterol esterase inhibition by IFA became irreversible after photolysis with UV light and oleic acid (1 mM) provided 50% protection against inactivation. Incubation of homogeneous bovine pancreatic cholesterol esterase with IFA:CEA resulted in its hydrolysis to IFA and cholesterol, indicating recognition of IFA:CEA as a substrate by cholesterol esterase. The coenzyme A ester, IFA:CoA, was a reversible inhibitor of microsomal ACAT activity under dark conditions (apparent Ki = 20 microM), and photolysis resulted in irreversible inhibition of enzyme activity with 87% efficiency. IFA:CoA was also recognized as a substrate by both liver and aortic microsomal ACATs, with resultant synthesis of 125IFA:CEA. IFA and its derivatives, IFA:CEA and IFA:CoA, are thus inhibitors and substrates for cholesterol esterase and ACAT. Biological recognition of these photoaffinity lipid analogues will facilitate the identification and structural analysis of hitherto uncharacterized protein lipid binding sites.

Acyl Coenzyme A↗
PubMed1978

Interaction of an amine oxide detergent with lecithin vesicles as studied by nuclear magnetic resonance.

The interaction of an amine oxide detergent with single bilayer lecithin vesicles was investigated with proton and phosphorus magnetic resonance. The addition of the detergent micelles to vesicles suspensions leads to rapid detergent incorporation into the vesicle bilayer, resulting in a heterogenous vesicle population. Initially, some vesicles take up the equivalent of one detergent micelle, whereas others contain no detergent. Subsequently, the detergent is distributed between the vesicles by vesicle-vesicle collisions. This can be followed by the change in the Pr3+-shifted spectral positions of the detergent and lecithin head groups with time. From the intensity of the head-group signals, it can be concluded that after about 20 h the detergent is almost equally distributed between the outer and inner vesicle membrane monolayers. Vesicles obtained by cosonication of the detergent and lecithin take up metal ions. This ion permeability depends on the vesicle concentration and can be attributed to vesicle-vesicle or vesicle-mixed micelle collisions. Egg lecithin vesicles are stable against the detergent up to molar ratios of detergent to lecithin of 0.2--0.3. At larger ratios mixed micells and multibilayers are formed. Measurements of proton spin-lattice relaxation times confirmed that the internal architecture of the vesicle bilayer is almost unaffected by the incorporated detergent.

Detergents↗
PubMed2001

Profile of changes in lipid bilayer structure caused by beta-amyloid peptide.

beta-Amyloid peptide (A beta) is the primary constituent of senile plaques, a defining feature of Alzheimer's disease. Aggregated A beta is toxic to neurons, but the mechanism of toxicity is uncertain. One hypothesis is that interactions between A beta aggregates and cell membranes mediate A beta toxicity. Previously, we described a positive correlation between the A beta aggregation state and surface hydrophobicity, and the ability of the peptide to decrease fluidity in the center of the membrane bilayer [Kremer, J. J., et al. (2000) Biochemistry 39, 10309--10318]. In this work, we report that A beta aggregates increased the steady-state anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) embedded in the hydrophobic center of the membrane in phospholipids with anionic, cationic, and zwitterionic headgroups, suggesting that specific charge--charge interactions are not required for A beta--membrane interactions. A beta did not affect the fluorescence lifetime of DPH, indicating that the increase in anisotropy is due to increased ordering of the phospholipid acyl chains rather than changes in water penetration into the bilayer interior. A beta aggregates affected membrane fluidity above, but not below, the lipid phase-transition temperature and did not alter the temperature or enthalpy of the phospholipid phase transition. A beta induced little to no change in membrane structure or water penetration near the bilayer surface. Overall, these results suggest that exposed hydrophobic patches on the A beta aggregates interact with the hydrophobic core of the lipid bilayer, leading to a reduction in membrane fluidity. Decreases in membrane fluidity could hamper functioning of cell surface receptors and ion channel proteins; such decreases have been associated with cellular toxicity.

2-Naphthylamine↗
PubMed2006

Glycerol monolaurate inhibits the effects of Gram-positive select agents on eukaryotic cells.

Many exotoxins of Gram-positive bacteria, such as superantigens [staphylococcal enterotoxins, toxic shock syndrome toxin-1 (TSST-1), and streptococcal pyrogenic exotoxins] and anthrax toxin are bioterrorism agents that cause diseases by immunostimulation or cytotoxicity. Glycerol monolaurate (GML), a fatty acid monoester found naturally in humans, has been reported to prevent synthesis of Gram-positive bacterial exotoxins. This study explored the ability of GML to inhibit the effects of exotoxins on mammalian cells and prevent rabbit lethality from TSS. GML (>or=10 microg/mL) inhibited superantigen (5 microg/mL) immunoproliferation, as determined by inhibition of (3)H-thymidine incorporation into DNA of human peripheral blood mononuclear cells (1 x 10(6) cells/mL) as well as phospholipase Cgamma1, suggesting inhibition of signal transduction. The compound (20 microg/mL) prevented superantigen (100 microg/mL) induced cytokine secretion by human vaginal epithelial cells (HVECs) as measured by ELISA. GML (250 microg) inhibited rabbit lethality as a result of TSST-1 administered vaginally. GML (10 microg/mL) inhibited HVEC and macrophage cytotoxicity by anthrax toxin, prevented erythrocyte lysis by purified hemolysins (staphylococcal alpha and beta) and culture fluids containing streptococcal and Bacillus anthracis hemolysins, and was nontoxic to mammalian cells (up to 100 microg/mL) and rabbits (250 microg). GML stabilized mammalian cell membranes, because erythrocyte lysis was reduced in the presence of hypotonic aqueous solutions (0-0.05 M saline) or staphylococcal alpha- and beta-hemolysins when erythrocytes were pretreated with GML. GML may be useful in the management of Gram-positive exotoxin illnesses; its action appears to be membrane stabilization with inhibition of signal transduction.

Animals↗
PubMed1997

Interactions of thionin from Pyrularia pubera with dipalmitoylphosphatidylglycerol large unilamellar vesicles.

The peptide toxin thionin from Pyrularia pubera binds to dipalmitoylphosphatidylglycerol (DPPG) large unilamellar vesicles as shown by an increase in the intensity and blue-shift of the fluorescence emission spectrum of the single tryptophan residue of the protein. The magnitude of these fluorescence changes increased with temperature near the thermotropic phase transition of DPPG (about 40 degrees C). Fluorescent probes sensitive to the structure and dynamics of the membrane were used to assess the effect of thionin binding on bilayer properties. The fluorescence emission spectra of Prodan, Patman, and Laurdan all showed spectral changes consistent with an increase in bilayer polarity at temperatures below the DPPG phase transition but a decrease in polarity at higher temperatures. Fluorescence polarization experiments and the ratio of monomer-to-excimer fluorescence of the probe 1,3-bis(1-pyrene)propane suggested that thionin increases the bilayer order above the transition temperature. Differential scanning calorimetry revealed that thionin broadens the transition and either increases or decreases the melting temperature depending on the concentration of the peptide. Taken together, the data are consistent with at least three distinct interactions of thionin with the bilayer: (1) thionin bound electrostatically to the bilayer surface; (2) tryptophan of the bound thionin inserted into the bilayer; (3) high-order aggregates of thionin-bound vesicles.

2-Naphthylamine↗