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A Kaplun

Publications and source records attributed to A Kaplun.

At least 19 recordsLinked to original sources
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

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↗
PubMed1995

Cholesterol precipitation from cholesterol-supersaturated bile models.

Bile-model systems containing cholesterol (CH), phosphatidylcholine (PC) and sodium cholate (NaC) at concentrations similar to those found in supersaturated human gall bladder bile ([CH]/[PC] = 0.60 +/- 0.01; CH saturation index, CSI = 1.58 +/- 0.03) were prepared by mixing PC-CH vesicles with NaC micellar solutions. Following mixing, the dispersion became transparent and gave rise to high resolution 1H-NMR spectra typical of mixed micellar systems. Cryo-transmission electron micrographs of specimens vitrified at that stage support the conclusion that the vesicles had become completely micellized. Following micellization, the metastable (cholesterol-supersaturated) bile-models spontaneously underwent a series of reorganizational steps: first, cholesterol-rich vesicles with a [CH]/[PC] ratio of 1.57 +/- 0.69 were formed, in co-existence with a mixed micellar system with [CH]/[PC] = 0.43 +/- 0.01 and CSI = 1.12 +/- 0.03. The resultant cholesterol-rich vesicles subsequently aggregated and cholesterol crystals of varying sizes and shapes appeared within the aggregates: needle-like structures were first observed, followed by clusters of those crystals and of helical crystals. Eventually, typical plate-like cholesterol crystals appeared, at which time some of the PC returned to the non-particulate (isotropic) phase. Consequently, the system contained cholesterol crystals coexisting with mixed micelles, whose composition was close to the limit of saturation (CSI = 1.08). These findings confirm the sequence of events preceding the appearance of cholesterol crystals, as previously proposed in our less detailed studies ((1990) Hepatology 12, 149S) and support the relevance of the morphologically similar results of Konikoff et al. ((1992) J. Clin. Invest. 90, 1155) obtained in a very dilute supersaturated bile-model.

Bile↗
PubMed1995

Interaction of N-(2-hydroxybenzyl)-omega-amino carbonic acids, novel amphipathic fatty acid derivatives, with membrane: partition coefficients.

The methods for partition coefficient (Kp) determination were developed for different concentrations of N-(2-hydroxybenzyl)-omega-amino carbonic acids, a new class of amphipathic fatty acid derivatives (An), their deutero (AnD) and bromine (AnBr) derivatives. To do this the following methods were used: 2H-NMR, equilibrium dialysis, centrifugation and fluorescence spectroscopy. Kp dependence on the An concentration is discussed. Kp values for AnBr were more than 120-times higher than those for An, the differences between them being smaller than those for the corresponding An. This series of new amphipathic compounds can be used as probes for membrane studies.

Bromine↗
PubMed1995

Structures of nanoparticles prepared from oil-in-water emulsions.

Hydrophobic substances were dissolved in an organic solvent and emulsified with an aqueous solution at very high shear. Droplets of very small sizes (50-100 nm) were obtained by using surfactants which were combinations of lecithins and bile salts. After emulsification, the organic solvent was removed by evaporation, yielding stable dispersions of solid particles. The sizes, shapes, and structures of the particles were examined through quasi-elastic light scattering, small-angle neutron scattering and cryotransmission electron microscopy. Cholesterol acetate particles stabilized by lecithin and bile salts were found to be platelets of 10-20 nm thickness and 80 nm diameter. Cholesteryl acetate particles stabilized with POE-(20)-sorbitan monolaurate were dense spherical globules of diameter 100 nm. Particles with a composition similar to the endogenously occurring, lipoprotein, LDL, were large spherical globules studded with small vesicles. The subsequent evolution of the cholesteryl acetate dispersion upon aging was examined. There was no transfer of cholesteryl acetate between particles nor to large crystals. However, some aggregation of the particles was observed when the volume fraction of the particles in the aqueous dispersion exceeded 0.05. Thus, the structure of the nanoparticles obtained through deswelling of emulsion droplets changes according to the nature of the emulsifiers and to the composition of the hydrophobic substances which they contain.

Bile Acids and Salts↗
PubMed1995

Effect of novel aromatic derivative of GABA on lipid peroxidation in chronically morphinized rats.

Effect of novel aromatic GABA derivative (AFA) on lipid peroxidation (LP) was studied in the male rats of the Wistar strain. The morphine-received animals had the higher level of LP in blood plasma, decreased level of total antioxidant activity, the increased rate of LP in the ascorbate-induced system in liver homogenate. In the case of AFA administration with morphine, all the above mentioned effects were almost withdrawn.

Animals↗
PubMed1994

Direct visualization of lipid aggregates in native human bile by light- and cryo-transmission electron-microscopy.

The evolution of microstructures present in human gallbladder and hepatic bile was observed simultaneously by video-enhanced light microscopy (VELM) and transmission electron microscopy of vitrified specimens (cryo-TEM), as a function of time after withdrawal from patients. Fresh centrifuged gallbladder bile samples contained small (6 nm) spherical micelles in coexistence with vesicles (40 nm). Out of the seven bile samples investigated four contained, in addition, two types of elongated aggregates that have not been previously described. Uncentrifuged gallbladder bile also contained a mixture of ribbon- and plate-like crystals seen by VELM, but not by cryo-TEM. In aged (3-6-week-old) gallbladder bile samples VELM also revealed spiral and helical crystal structures. No such crystals were present in hepatic bile samples, although microcrystals, not observable by VELM were seen by cryo-TEM in addition to micelles and vesicles. The similarity of these observations to those observed in bile models lends strong support for the validity of the model systems. Furthermore, the presence of microcrystals in hepatic bile samples, apparently devoid of crystals by light microscopy, indicates that under certain conditions the common criterion of 'nucleation time' (NT), based on light microscopy, does not represent the real time of nucleation. In the human bile samples investigated in this study the dissociation between NT and the time of observation of microcrystals was seen in hepatic but not in gallbladder bile samples. Hence, crystal growth may be rate limiting only in dilute biles.

Bile↗
PubMed1993

N-(2-hydroxybenzyl)-omega-amino carbonic acids and their derivatives as tools for biochemical and biophysical investigations.

We propose N-(2-hydroxybenzyl)-omega-amino carbonic acids (An) as multifunctional probes for fatty acid metabolism studies. Multifunctionality could be achieved by introduction of different isotopes into An molecule. Deuteration of An results in probes for 2H-NMR membrane studies. Introduction of radioactive iodine and bromine isotopes into An gives diagnosticums for gamma-tomography and PET. AnI and AnBr are fluorescence quenchers usable for membrane studies. This multifunctionality of An derivatives is valuable because they participate in such metabolic pathways of fatty acids as beta-oxidation and inclusion into lipids. They can also inhibit natural FA oxidation.

Animals↗
PubMed1986

Haem localization in haemoproteins by spin and triplet tools.

The rate constants of efficient exchange interaction (kex) of spin-labelled lysozyme and the triplet probes perylene, eosine and anthracene butanoic acid with the haemoproteins were measured in microsomes and in solution by electron paramagnetic resonance and by the registration of delayed annihilation fluorescence. Constants of efficient exchange interactions with the haem groups of myoglobin, haemoglobin, cytochrome c and b5 are 3-22 X 10(7) M-1 s-1 in solution. The experiments with membrane-bound cytochrome P-450 revealed no exchange interactions with the probes located in solution or in the membrane. These results can be accounted for by the deeper incorporation of cytochrome P-450 haem into the protein globule as compared to the other haemoprotein haems studied.

Animals↗
PubMed1984

A model for adhesion formation by thermal injury in the abdominal cavity of the mouse.

An experimental model for inducing peritoneal adhesions in mice is described. Measurable thermal trauma can be inflicted by the application of a heated metal object, for a given lapse of time, to the surface of a section of mouse intestine. Parameters of temperature, area and application time were so manipulated as to obtain adhesions in only 70-75% of treated mice. It is maintained that this model can enable better evaluation of various prophylactic means and also the detection of exacerbating agents.

Animals↗
PubMed1984

Cellular events in adhesion formation due to thermal trauma.

Consequent to thermal traumatization of the intestinal wall of the mouse, histopathological events ensue which lead to peritoneal adhesion formation. In the first 48 h, the main pathological findings are of a necrotic and inflammatory nature, but subsequently fibroplasia is the main feature, as evidenced by the appearance of spindle-shaped cells followed by fibroblasts. Factors essential for and contributing to the formation of adhesions are described.

Animals↗
PubMed1983

Correlation between chemiluminescence response and rate of zymosan uptake by rat alveolar macrophages. Scanning electron microscope observations.

The rate of particle uptake by rat alveolar macrophages (AM) exposed to zymosan (mean number of zymosan particles becoming bound to 100 cells at a fixed time interval) was determined with the aid of the scanning electron microscope (SEM). The intensity of the chemiluminescence (CL) emitted by the AM on addition of zymosan, was measured concomitantly. During the whole course of CL emission, all the particles were found to be either attached or engulfed, but not ingested by the AM. A good correlation was obtained between the time dependence of CL intensity and that of the rate of particle uptake, both reaching a peak value at about 5 min after exposure. It is therefore assumed that the CL emitted by AM exposed to zymosan reflects the attachment and engulfment stages of phagocytosis.

Animals↗
PubMed1983

Macrophage heterogeneity in thromboplastin response.

The procoagulant activities of non-elicited mouse monocytes/macrophages from four anatomical localizations were compared. These cell populations were further examined for their ability to increase their procoagulant activity on exposure to endotoxin or phytohaemagglutinin (PHA). Peritoneal macrophages exhibited the highest basal procoagulant activity. Their activity was further enhanced by stimulation with endotoxin and PHA, but marked strain differences were noted. This procoagulant has been identified as tissue thromboplastin. Isolated adherent spleen cells, peripheral blood monocytes or lung alveolar macrophages had a low basal procoagulant activity that did not increase on exposure to PHA or endotoxin. The identity of the weak procoagulant in these cells is uncertain. The presence of lymphocytes in the macrophage cultures (4:1 ratio) enhanced slightly (1.3 to 1.5-fold) the response of peritoneal macrophages to endotoxin or PHA but did not significantly influence the procoagulant activity of the other macrophage subpopulations under the conditions tested. These results demonstrate heterogeneity among different macrophage subpopulations with regard to cellular procoagulant expression.

Animals↗
PubMed1983

Synthesis of thromboplastin (factor III) in mouse placental cells in vitro.

Mouse placental cells have been isolated and grown in cultures. These cells produce a procoagulant which is identical to thromboplastin (factor III) by two criteria. The procoagulant activity increases with time, culminating on the 5th day of culture. The increase is inhibited by cycloheximide, alpha-amanitin, and actinomycin D, showing that de novo synthesis of protein and RNA is necessary. About 90-95% of the total cellular thromboplastin activity in whole cells is available for inactivation by particle-bound trypsin and thus present on the cell surface. Endotoxin and phytohaemagglutinin did not further increase the procoagulant activity.

Amanitins↗