Biomedical subjects

Y Talmon

Publications and source records attributed to Y Talmon.

At least 19 recordsLinked to original sources

PubMed2006

Structural and dynamical properties of ribbonlike self-assemblies of a fluorinated cationic surfactant.

The structural and dynamic properties of low ionic strength micellar solutions of the cationic surfactant perfluorooctylbutane trimethylammonium bromide have been investigated by cryo-TEM, small-angle neutron scattering, small-angle X-ray scattering, T-jump and rheological experiments. The surfactant molecules self-assemble into narrow ribbons with average dimensions on the order of 4 nm x 3 nm, either under salt-free conditions or in the presence of up to 30 mM KBr or NaF. Cryo-TEM also reveals in the salt-free systems the presence of networks of multiconnected micelles. Rheological experiments showed that these surfactant systems exhibit a strong shear-thickening effect even in the presence of up to 30 mM KBr. The T-jump response of the micellar solutions was found to be multiexponential. This observation rules out the presence of only linear micelles with an exponential length distribution and suggests more complex topologies of the micellar aggregates. The relaxation time associated with the predominant process in the T-jump relaxation is strongly correlated to the critical shear rate beyond which shear thickening occurs, thus indicating that this critical shear rate is controlled by the micellar kinetics.

Journal Article↗

PubMed2005

Effect of the spacer length on the association and adsorption behavior of dissymmetric gemini surfactants.

A series of dissymmetric gemini surfactants with the general formula [C12H25(CH3)2N(CH2)sN(CH3)2C14H29]Br2 designed as 12-s-14, where s=2, 6, and 10, were synthesized and their physicochemical properties investigated. The effect of spacer length on Krafft temperature, adsorption at the air/solution interface, and association in aqueous solution was studied by tensiometry, conductometry, and cryo-transmission electron microscopy. The Krafft temperature was found to increase linearly with spacer length. In the submicellar concentration range the dissymmetric 12-s-14 surfactants display ion pairing and premicellar association. Adsorption at air/solution interfaces and micellization in aqueous solution are similar to the behavior of their symmetric counterparts and depend strongly on spacer length.

Journal Article↗

PubMed2004

Microstructural characterization of micro- and nanoparticles formed by polymer-surfactant interactions.

We have studied the nano- and microparticles formed by complexation of PDAC [poly(diallyldimethyl-ammoniumchloride)] and SDS (sodium dodecyl sulfate). The complexation phenomenon was characterized by light scattering and zeta-potential measurements. The nature of the complexes was revealed by direct-imaging cryogenic temperature transmission electron microscopy (cryo-TEM), showing nanometric details of the complexes formed around the point of neutralization. The images also reveal how those aggregates are solubilized by excess surfactant, first into faceted particles with threadlike micelles attached to their surfaces, prior to complete solubilization, then into lacelike aggregates, and finally into spheroidal micelles. The nanostructure of the complexes strongly suggests they are made of a hexagonal liquid crystalline phase. This was further supported by small-angle X-ray scattering (SAXS).

Journal Article↗

PubMed2002

Microscopics of complexation between long DNA molecules and positively charged colloids.

Extensive atomic force and electron microscopy reveal a new, generic DNA-colloid complex with a fixed number of DNA bases per colloid. The fiber shaped complex is stable in the presence of excess colloids in the solution. As more DNA is added to the solution and the ratio between colloids and DNA approaches the fiber's stoichiometry, the system undergoes a sharp coagulation transition. The system is restabilized at even higher DNA concentrations through localization of small colloid clusters on extensive DNA networks.

Bacteriophage lambda↗

PubMed2001

Phase behavior, DNA ordering, and size instability of cationic lipoplexes. Relevance to optimal transfection activity.

Mechanisms of cationic lipid-based nucleic acid delivery are receiving increasing attention, but despite this the factors that determine high or low activity of lipoplexes are poorly understood. This study is focused on the fine structure of cationic lipid-DNA complexes (lipoplexes) and its relevance to transfection efficiency. Monocationic (N-(1-(2,3-dioleoyloxy)propyl),N,N,N-trimethylammonium chloride, N-(1-(2,3-dimyristyloxypropyl)-N,N-dimethyl-(2-hydroxyethyl)ammonium bromide) and polycationic (2,3-dioleyloxy-N-[2(sperminecarboxamido)ethyl]-N,N-dimethyl-1-propanammonium trifluoroacetate) lipid-based assemblies, with or without neutral lipid (1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine, 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine, cholesterol) were used to prepare lipoplexes of different L(+)/DNA(-) charge ratios. Circular dichroism, cryogenic-transmission electron microscopy, and static light scattering were used for lipoplex characterization, whereas expression of human growth hormone or green fluorescent protein was used to quantify transfection efficiency. All monocationic lipids in the presence of inverted hexagonal phase-promoting helper lipids (1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine, cholesterol) induced appearance of Psi(-) DNA, a chiral tertiary DNA structure. The formation of Psi(-) DNA was also dependent on cationic lipid-DNA charge ratio. On the other hand, monocationic lipids either alone or with 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine as helper lipid, or polycationic 2,3-dioleyloxy-N-[2(sperminecarboxamido)ethyl]-N,N-dimethyl-1-propanammonium trifluoroacetate-based assemblies, neither of which promotes a lipid-DNA hexagonal phase, did not induce the formation of Psi(-) DNA. Parallel transfection studies reveal that the size and phase instability of the lipoplexes, and not the formation of Psi(-) DNA structure, correlate with optimal transfection.

3T3 Cells↗

PubMed2001

Formation of complement-activating particles in aqueous solutions of Taxol: possible role in hypersensitivity reactions.

We reported earlier that the anticancer drug paclitaxel (Taxol) activated the complement (C) system in human serum in vitro, raising the possibility that C activation might play a role in the ill-understood hypersensitivity reactions (HSRs) to this drug [J. Natl. Cancer Inst. 90 (1998) 300]. In pursuing the mechanism of C activation by Taxol, the present study provided evidence that dilution of the injection concentrate in aqueous solvents led to the formation of micelles and needle-like structures, both of which caused C activation in vitro. Micelles were formed mainly from Cremophor EL (CrEL), the nonionic emulsifier vehicle of paclitaxel, whose level in Taxol infusion exceeded its critical micelle concentration by at least 400-fold. CrEL micelles were shown by quasi-elastic light scattering and cryo-transmission electron microscopy (cryo-TEM) to be spherical with diameters in the 8-22 nm range; however, de novo formation of 50-300 nm microdroplets following incubation with human plasma suggested further fundamental structural transformation in blood. The needle-like structures extended to the multimicron range and were shown by electron diffraction to be crystalline paclitaxel. Taxol-induced C activation was manifested in varying rises of serum C3a-desarg, iC3b and SC5b-9. The causal role of CrEL micelles in C activation was demonstrated by the fact that filtration of aqueous solutions of Taxol or pure CrEL via 30-kDa cutoff filters eliminated, while the filter retentate restored C activation. C activation by Taxol was also inhibited by 10 mg/ml human immunoglobulin (IVIG). If proven clinically, HSRs to Taxol may represent a hitherto vaguely classified adverse drug reaction recently called C activation-related pseudoallergy (CARPA) [Circulation 99 (1999) 2302].

Antineoplastic Agents, Phytogenic↗

PubMed2001

Self-made tooth guard using Turbocast.

Tooth protection during suspension microlaryngeal surgery is a challenge when teeth are damaged or missing. We present an effective, disposable and cheap tooth guard for microlaryngeal surgical procedures using Turbocast. The tooth guard transits the laryngoscope's pressure directly to the hard palate leaving the teeth uninvolved and free of any pressure.

Disposable Equipment↗

PubMed2001

Vascular transformation of lymph node sinuses.

Vascular transformation of lymph node sinuses is an uncommon condition and only isolated cases have been reported. It is characterized by conversion of nodal sinuses into capillary-like channels, often accompanied by fibrosis. Venous or lymphatic obstruction is thought to be the underlying mechanism, and in most cases factors that may contribute to lymphovascular obstruction can be identified such as tumour in the vicinity, vascular thrombosis, heart failure, previous surgery or radiotherapy. Most cases involve abdominal lymph nodes, and head and neck involvement is rare. We present two cases of vascular transformation of lymph node sinuses presenting only as cervical lymphadenopathy, without an obvious cause of lymphovascular obstruction.

Adult↗

PubMed2001

Medium-term middle ear ventilation with self-manufactured polyethylene T-tubes for the treatment of children with middle ear effusion.

We present the results of the insertion of self-made polyethylene T-tubes for a period of 15-24 months for the treatment of chronic middle-ear effusion. We compare the outcome of our patients to the reported outcome of patients treated with other commonly used ventilation tubes for either shorter or longer periods of time. In a retrospective review of 603 T-tubes inserted in 306 children up to the age of 12 years, charts were reviewed for age, sex, surgical procedure performed, duration of ventilation and complications. In all cases the indication for surgery was chronic middle-ear effusion. The tubes were electively removed by the authors after 15-24 months of ventilation. Spontaneous extrusion was considered a complication. The mean period of ventilation was 20 months. Post-operative otorrhoea was experienced in 6.6 per cent of ears; 4.8 per cent of tubes extruded spontaneously, whereas 3.15 per cent had to be removed earlier than originally planned; 4.9 per cent of ears were re-ventilated at a later date, and 1.49 per cent of ears developed a persistent perforation. We demonstrate that the outcome of patients treated with our self-manufactured tubes for a period of 15-24 months is, in many respects, better or at least comparable to the reported outcome of patients treated with other commonly used ventilation tubes for either shorter or longer periods of time, and that the many complications associated with the conventional T-tube can be reduced. We suggest that our favourable outcome may be due to the duration of ventilation, which was controlled to be shorter than the conventional long-term T-tubes and longer than that of grommets.

Child↗

PubMed2001

[Verrucous carcinoma of the nose and maxillary sinus].

Verrucous carcinoma is a rare type of squamous cell carcinoma that is most commonly seen in the oral cavity, and seldom in the larynx. It should be distinguished from benign papilloma, verrucous hyperplasia and well-differentiated non verrucous squamous cell carcinoma. Verrucous carcinoma is a rare tumor of the sinonasal tract. Only 28 such cases have been described in the medical literature reviewed until this time. We describe the first case in Israel of a patient with such a tumor in the nasal cavity. We reviewed the existing literature dealing with Verrucous Carcinoma of paranasal sinuses.

Aged↗

PubMed2000

Microstructural evolution of lipid aggregates in nucleating model and human biles visualized by cryogenic transmission electron microscopy.

Obtaining reliable information on the physical state and ultrastructure of bile is difficult because of its mixed aqueous-lipid composition and thermodynamic metastability. We have used time-lapse cryogenic transmission electron microscopy (cryo-TEM) combined with video-enhanced light microscopy (VELM) to study microstructural evolution in nucleating bile. A well-characterized model bile and gallbladder biles from cholesterol and pigment gallstone patients were studied sequentially during cholesterol nucleation and precipitation. In model bile, cholesterol crystallization was preceded by the appearance of the following distinct microstructures: spheroidal micelles (3-5 nm), discoidal membrane patches (50-150 nm) often in multiple layers (2-10), discs (50-100 nm), and unilamellar (50-200 nm) and larger multilamellar vesicles (MLVs). The membrane patches and discs appeared to be short-lived intermediates in a micelle-to-vesicle transition. Vesicular structures formed by growth and closure of patches as well as by budding off from vesicles with fewer bilayers. MLVs became more abundant, uniform, and concentric as a function of time. In native bile, all the above microstructures, except discoidal membrane patches, were observed. However, native MLVs were more uniform and concentric from the beginning. When cholesterol crystals appeared by light microscopy, MLVs were always detected by cryo-TEM. Edges of early cholesterol crystals were lined up with micelles and MLVs in a way suggesting an active role in feeding crystal growth from these microstructures. These findings, for the first time documented by cryo-TEM in human bile, provide a microstructural framework that can serve as a basis for investigation of specific factors that influence biliary cholesterol nucleation and crystal formation.

Bile↗

PubMed2000

Total inferior turbinectomy: operative results and technique.

The internal nasal structures, including the turbinates, regulate the nasal airflow. The surgical treatment of turbinate hypertrophy remains controversial. A wide variety of surgical procedures is performed, with universally unsatisfactory results. Interference with nasal physiology and possible postoperative complications have been the main reasons for the objection to total inferior turbinectomy. Over a 6-year period, 357 total inferior bilateral turbinectomies were performed at our institution. We present the results of these procedures and describe our surgical technique. We conclude that even in a hot and dusty climate, total inferior turbinectomy is an effective and relatively safe procedure.

Adolescent↗

PubMed1999

The effect of long-term antipsychotic treatment on the body weight of patients suffering from chronic schizophrenia: clozapine versus classical antipsychotic agents.

The aim of this study was to evaluate the effect of long-term clozapine treatment on body weight changes in neuroleptic-resistant chronic schizophrenic patients and to compare it with that of classical antipsychotic agents. The body mass index (BMI) of 96 neuroleptic-resistant chronic schizophrenic patients was calculated before the beginning and after long-term (mean +/- SD 1.7 +/- 1.3 years) clozapine treatment. These data were compared to the BMI of 98 chronic schizophrenic patients maintained on classical antipsychotic agents for a similar duration (mean +/- SD 1.9 +/- 1.6 years). A significant elevation in BMI was detected in both groups during these periods (P < 0.0001 versus baseline, for both groups). The change in BMI (delta BMI) was similar in both groups (P < 0.9). We conclude that the increase in body weight caused by long-term (> 6 months) clozapine treatment is comparable to that obtained following long-term classical antipsychotic agents treatment.

Adult↗

PubMed1998

Lyotropic Liquid Crystalline Phases from Symmetric Double-Tailed Surfactants: Sodium 1'-(6)-Undecylbenzenesulfonate, 1'-(7)-Tridecylbenzenesulfonate, and 1'-(8)- Pentadecylbenzenesulfonate in Water.

Phase diagrams of binary symmetric double-tailed alkylbenzenesulfonate surfactant/water systems, as well as the structure of the phases, were determined using crossed polars, polarized light microscopy, 2H NMR spectroscopy, Nomarski differential interference contrast optics, and cryo-transmission electron microscopy. The isotropic phase, the lamellar phase, and a high-viscosity solution representing an intermediate between the isotropic phase and the mesophase, which refers to the beginning of the formation of vesicles, were found. As may be expected, the isotropic phases at higher concentrations are formed mostly at higher temperatures. Isotropic regions are followed by regions characterized as the isotropic solutions containing vesicles; the optically isotropic phase contains a lamellar dispersion of vesicles in solution. The viscosity of these phases is found to be high near the borderline of the two-phase regions. At the same concentrations two-phase regions were found to contain the isotropic + lamellar phases at the higher temperature and the isotropic + crystalline phase at the lower temperature. Molecular-mechanical and semiempirical quantum-mechanical calculation searches for the global minimum in the conformational space of alkylbenzenesulfonate ions were conducted to examine the influence of monomer molecular structure on the micellar shape. Copyright 1998 Academic Press.

Journal Article↗

PubMed1998

Direct imaging by cryo-TEM shows membrane break-up by phospholipase A2 enzymatic activity.

Phospholipid hydrolysis to free fatty acid and 1-lyso-phospholipid by water-soluble phospholipase A2 (PLA2) at the surface of lipid membranes exhibits a poorly understood transition from a low-activity lag phase to a burst regime of rapid hydrolysis. Understanding this kinetic phenomenon may increase our insight into the function of PLA2 under physiological conditions as well as into general interfacial catalysis. In the present study we apply for the first time cryo-transmission electron microscopy (cryo-TEM) and high-performance liquid chromatography (HPLC) to characterize the PLA2 hydrolysis of phospholipid vesicles with respect to changes in lipid composition and morphology. Our direct experimental results show that the initial reaction conditions are strongly perturbed during the course of hydrolysis. Most strikingly, cryo-TEM reveals that starting in the lag phase, vesicles become perforated and degrade into open vesicles, bilayer fragments, and micelles. This structural instability extends throughout the system in the activity burst regime. In agreement with earlier reported correlations between initial phospholipase activity and substrate morphology, our results suggest that the lag-burst phenomenon reflects a cascade process. The PLA2-induced changes in lipid composition transform the morphology which in turn results in an acceleration of the rate of hydrolysis because of a strong coupling between the PLA2 activity and the morphology of the lipid suspension.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1997

Imaging supramolecular aggregates in bile models and human bile.

Investigation of cholesterol crystallization is essential for the understanding of gallstone formation. Previous work has revealed a variety of aggregates of different sizes and shapes prior to the appearance of "classical" plate-like cholesterol monohydrate crystals both in native biles and model systems. In this article, we review existing data based on various microscopic techniques and present data on microstructural pathways leading to cholesterol crystal formation in two different bile models and in native bile. In continuation of our recent investigation of microstructures in nucleating human bile, we now present data suggesting that polymorphism is not limited to complex native bile, but also appears in two, simplified model systems. These studies employed cryo-transmission electron microscopy (cryo-TEM) and video-enhanced light microscopy, using Nomarski optics (VELM). Only the combined use of these two complementary, non-perturbing direct methods can cover the whole range of microstructures ranging from a few nanometers to several microns. Concentrated isotropic solutions of bile models, composed of cholesterol, lecithin and taurocholate, were diluted to induce cholesterol supersaturation and start an evolution of microstructures, leading to cholesterol crystallization. Initially, small spheroidal micelles were observed by cryo-TEM. Subsequently, uni-, oligo- and multilamellar vesicles, compatible with structures seen at the same time by VELM, appeared in coexistence with micelles. Thereafter, during a dynamic phase of cholesterol crystallization, filaments, tubular and helical microstructures, as well as classical plate-like cholesterol monohydrate crystals were noted by light microscopy. Eventually, large plate-like crystals were observed by VELM, while cryo-TEM revealed only small spheroidal micelles. The crystallization process in native human bile during ex vivo incubation was found to bear close resemblance to the findings in the model systems, further supporting the applicability of these systems to the exploration of microstructural aspects of nucleating human bile.

Bile↗

PubMed1997

Aggregation and Microstructure in Aqueous Solutions of the Nonionic Surfactant C12E8

Mixtures of water and of the nonionic surfactant C12E8 (octaoxyethyleneglycol monododecylether) have been investigated by time-resolved fluorescence quenching (TRFQ) and transmission electron microscopy at cryogenic temperature (cryo-TEM) to obtain information on the size and shape of the surfactant aggregates and on the microstructure of the mixtures. The studies were performed at surfactant contents and temperatures where the micelles grew significantly and also where the systems undergo phase transitions from micellar-to-cubic upon increasing surfactant content or decreasing temperature and from cubic-to-hexagonal-to-micellar upon increasing temperature. No rapid change or discontinuity was observed in the variation of the aggregation number with the surfactant content or temperature upon crossing the micellar-to-cubic phase boundary nor at the approach of the hexagonal phase from the cubic phase. The results confirmed that the cubic phase consists of spheroidal micelles forming a three-dimensional array. The aggregation numbers at high surfactant content or temperature can be much larger than that of the minimum spherical micelle for a surfactant with a dodecyl chain, suggesting that the micelles should be anisotropic. However, cryo-TEM showed that in the micellar phase the micelles are always spheroidal. These apparently inconsistent results are explained in terms of a partial mixing of the surfactant dodecyl chains and octaoxyethylene head groups which allows for spheroidal micelles of aggregation number much larger than for a surfactant with a dodecyl chain. The results show extensive exchange of material at 40°C, taking place most likely via temporary merging of micelles in micelle clusters then present in the system.

Journal Article↗

PubMed1997

Cryo-TEM and NMR studies of a micelle-forming phosphoglucolipid from membranes of Acholeplasma laidlawii A and B.

The chemical structure of a phosphoglucolipid from the membrane of the bacterium Acholeplasma laidlawii strain B-PG9 has been determined by high resolution NMR to be 1,2-diacyl-3-O-[glycerophosphoryl-6-O-(alpha-D-glucopyranosyl-(1 -->2)-O-alpha-D-glucopyranosyl)]-sn-glycerol (GPDGlcDAG). It was concluded that this lipid has exactly the same structure as one of the phosphoglucolipids from A. laidlawii strain A-EF22. By cryo transmission electron microscopy (cryo-TEM) and NMR diffusion techniques it was shown that, in highly diluted aqueous solutions, this membrane lipid forms long thread-like micelles in equilibrium with lipid vesicles. The cause of the occurrence of these different aggregates is discussed in terms of the varying molecular shapes of the lipid because of a heterogeneous composition of the acyl chains. A second membrane phosphoglucolipid from the bacterium, namely 1,2-diacyl-3-O-[glycerophosphoryl-6-O-(alpha-D- glucopyranosyl-(1 -->2)-monoacylglycerophosphoryl-6-O-alpha-D-glucopyranosyl)]-sn-gl ycerol (MABGPDGlcDAG), was found to form only a lamellar liquid crystalline phase coexisting with water.

Acholeplasma laidlawii↗