117,407 research outputs found
Probing membrane permeabilization by the antibiotic lipopeptaibol trichogin GA IV in a tethered bilayer lipid membrane
No full textAbstractThe lipopeptaibol trichogin GA IV (TCG) can be incorporated in the lipid bilayer moiety of a mercury-supported tethered bilayer lipid membrane (tBLM) at a non-physiological transmembrane potential of about −240mV, negative on the trans side of the bilayer. Once incorporated in the tBLM, TCG is stable over the range of physiological transmembrane potentials and permeabilizes the membrane at transmembrane potentials negative of −80÷−90mV. The chronocoulometric behavior is consistent with a kinetics of nucleation and growth of bundles of TCG building blocks with ion-channel properties. The TCG building blocks also permeabilize the lipid bilayer, albeit at more negative transmembrane potentials, and can be tentatively regarded as dimers of aligned TCG helical monomers. The cyclic voltammograms of tBLMs incorporating TCG point to a voltage-gated behavior of the TCG channel, similar to that exhibited by the peptaibol alamethicin
Au25(SCnH2 n+1)18 Clusters in Biomimetic Membranes: Role of Size, Charge, and Transmembrane Potential in Direct Membrane Permeation
No full textGold nanoclusters and nanoparticles are promising materials for applications in nanomedicine, and therefore, understanding their interaction with cell membranes is of particular importance. A series of neutral and anionic Au25(SCnH2n+1)18 monolayer protected clusters (MPCs) (briefly, Cn0 and Cn- clusters), was embedded into two types of biomimetic membranes supported by mercury electrodes. The first was a dioleoylphosphatidylcholine (DOPC) self-assembled monolayer (SAM), whereas the second was a tethered bilayer lipid membrane (tBLM) obtained by first anchoring a thiolipid monolayer to the mercury surface and then self-assembling a DOPC monolayer on top of it. The diameter of these clusters, from 1.7 to 2.7 nm depending on the thiolate ligand, is smaller than the thickness of biomembranes and biomimetic membranes. Both neutral and anionic Au25(SCnH2n+1)18 MPCs can penetrate the lipid bilayer moiety of the tBLM, without disrupting it; in particular, anionic Au25 clusters require positive transmembrane potentials to do so. Neutral Au25 clusters exchange one electron with mercury in a DOPC SAM, where they can come in contact with the mercury surface, whereas they are prevented from doing so at the tBLM because of their inability to cross the hydrophilic chain separating the lipid bilayer moiety from the mercury surface. The potential of these Au25 clusters to penetrate directly the plasma membrane is particularly convenient for targeted drug delivery. They are highly stable, biocompatible, and catalytic, and their uniform size is of importance in nanomedicine. Moreover, they may induce an efficient energy transfer to 3O2, allowing applications in radiotherapy and antimicrobial activity.
A procedure for estimating the surface dipole potential of monolayers adsorbed on electrodes
No full textEffect of a Strong Interfacial Electric Field on the Orientationof the Dipole Moment of Thiolated Aib-Oligopeptides Tetheredto Mercury on Either the N- or C-Terminus
No full textFour oligopeptides consisting of a sequence of R-aminoisobutyric acid (Aib) residues, thiolated
at either the N- or C-terminus by means of a -(CH2)2-SH anchor, were self-assembled on mercury, which
is a substrate known to impart a high fluidity to self-assembled monolayers (SAMs). The surface dipole
potential of these peptide SAMs was estimated in 0.1 M KCl aqueous solution at a negatively charged
electrode, where the interfacial electric field is directed toward the metal. To the best of our knowledge,
this is the first estimate of the surface dipole potential of peptide SAMs in aqueous solution. The procedure
adopted consisted in measuring the charge involved in the gradual expansion of a peptide-coated mercury
drop and then combining the resulting information with an estimate of the charge density experienced by
diffuse layer ions. The dipole moment of the tethered thiolated peptides was found to be directed toward
the metal, independent of whether they were thiolated at the C- or N-terminus. This result was confirmed
by the effect of these SAMs on the kinetics and thermodynamics of the Eu(III)/Eu(II) redox couple. The
combined outcome of these studies indicates that a strong interfacial electric field orients the dipole moment
of peptide SAMs tethered to mercury, even against their “natural” dipole moment
Incorporation of channel-forming peptides in a Hg-supported lipid bilayer
No full textThe channel-forming peptides gramicidin and alamethicin were incorporated in a mercury-supported lipid bilayer composed of a tethered thiolipid monolayer with a self-assembled dioleoylphosphatidylcholine monolayer on top of it. The thiolipid consists of a hexapeptide chain with a high tendency to form a 310-helical structure, which terminates at the N-terminus end with a sulfydryl group for anchoring to the metal while the C-terminus end is covalently linked to the polar head of dimyristolylphosphatidylethanolamine. The hexapeptide moiety has two triethyleneoxy side chains that impart a satisfactory hydrophilicity and are intended to keep the anchored thiolpeptide chains sufficiently apart, so as to accommodate water molecules and inorganic ions and to create a suitable environment for the incorporation of integral proteins. Changes in the conductance of this biomimetic membrane following the incorporation of gramicidin and alamethicin were detected by impedance spectroscopy. The surface dipole potential of the hexapeptide chain and the transmembrane potential of the lipid bilayer were estimated by using a simple electrostatic model of the mercury|solution interphase
Mechanisms of action of spa therapies in rheumatic diseases: what scientific evidence is there?
No full textSpa therapy represents a popular treatment for many rheumatic diseases. The mechanisms by which immersion in mineral or thermal water or the application of mud alleviates suffering in rheumatic diseases are not fully understood. The net benefit is probably the result of a combination of factors, with mechanical, thermal and chemical effects among the most prominent ones. Buoyancy, immersion, resistance and temperature all play important roles. According to the gate theory, pain relief may be due to the pressure and temperature of the water on skin; hot stimuli may influence muscle tone and pain intensity, helping to reduce muscle spasm and to increase the pain threshold. Mud-bath therapy increases plasma β-endorphin levels and secretion of corticotrophin, cortisol, growth hormone and prolactin. It has recently been demonstrated that thermal mud-pack therapy induces a reduction in the circulating levels of prostaglandin E2 (PGE2), leukotriene B4 (LTB4), interleukin-1β (IL-1β) and tumour necrosis factor-α (TNF-α), important mediators of inflammation and pain. Spa therapy has been found to cause an increase in insulin-like growth factor-1 (IGF1), which stimulates cartilage metabolism, and transforming growth factor-β (TGF-β). There is also evidence of the positive action of mud-packs and thermal baths on the oxidant/antioxidant system, with a reduction in the release of reactive oxygen (ROS) and nitrogen (RNS) species. Overall, thermal stress has an immunosuppressive effect. Many other non-specific factors may also contribute to the beneficial effects observed after spa therapy in some rheumatic diseases, including effects on cardiovascular risk factors, and changes in the environment, pleasant surroundings and the absence of work duties
Confini tra disturbo ossessivo-compulsivo e depressione: Considerazioni psicopatologiche
No full textAt first sight, obsessivity and depression seem to be two different phenomena, even opposite in some aspects. However, it is clinically common to find obsessive-compulsive features together with depressive symptoms: Whereas the discriminant power of self-report questionnaires for obsessions and compulsions is not very high when Obsessive-Compulsive Disorders and Major Depression are compared. However, clinical and biological studies suggest a clear discrimination between this two disorders. The psycopathological analisys allows both to understand the apparent analogies and to show the essential structural differences between obsessive-compulsive and depressive phenomena
Induced psoriasis after rituximab therapy for rheumatoid arthritis: a case report and review of the literature
No full textRituximab is a human/murine monoclonal antibody targeting the CD20 antigen on B-lymphocytes surface. Although it has been licensed for treatment of non-Hodgkin's lymphoma, nowadays it is also a novel therapy for autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus. Despite the increasing evidence regarding the safety and efficacy of rituximab in these conditions, many cutaneous adverse events have been reported. Here, we describe the case of a 69-year-old patient, affected by rheumatoid arthritis, who developed psoriatic lesions on her trunk and arms, three months after the second course of rituximab. Similar cases appearing in the literature will also be briefly mentioned. © 2012 Springer-Verlag Berlin Heidelberg
Tehered bilayer lipid micromembranes for single-channel recording: the role of adsorbed and partially fused vesicles
No full textA mercury-supported bilayer lipid micromembrane was prepared by anchoring a thiolipid monolayer to a mercury cap electrodeposited on a platinum microdisc about 20 mu m in diameter; a lipid monolayer was then self-assembled on top of the thiolipid monolayer either by vesicle fusion or by spilling a few drops of a lipid solution in chloroform on the cap and allowing the solvent to evaporate. Single-channel recording following incorporation of the alamethicin channel-forming peptide exhibits quite different features, depending on the procedure followed to form the distal lipid monolayer. The "spilling" procedure, which avoids the formation of adsorbed or partially fused vesicles, yields very sharp single-channel currents lasting only one or two milliseconds. These are ascribed to ionic flux into the hydrophilic spacer moiety of the thiolipid. Conversely, the vesicle-fusion procedure yields much longer single-channel openings analogous to those obtained with conventional bilayer lipid membranes, albeit smaller. This difference in behavior is explained by ascribing the latter single-channel currents to ionic flux into vesicles adsorbed and/or partially fused onto the tethered lipid bilayer, via capacitive coupling
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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