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Ellen Wachtel

Publications and source records attributed to Ellen Wachtel.

13 recordsLinked to original sources
PubMed2006

Age-related accumulation of pentosidine in aggrecan and collagen from normal and degenerate human intervertebral discs.

During aging and degeneration, many changes occur in the structure and composition of human cartilaginous tissues, which include the accumulation of the AGE (advanced glycation end-product), pentosidine, in long-lived proteins. In the present study, we investigated the accumulation of pentosidine in constituents of the human IVD (intervertebral disc), i.e. collagen, aggrecan-derived PG (proteoglycan) (A1) and its fractions (A1D1-A1D6) in health and pathology. We found that, after maturity, pentosidine accumulates with age. Over the age range studied, a linear 6-fold increase was observed in pentosidine accumulation for A1 and collagen with respective rates of 0.12 and 0.66 nmol x (g of protein)(-1) x year(-1). Using previously reported protein turnover rate constants (k(T)) obtained from measurements of the D-isomer of aspartic residue in collagen and aggrecan of human IVD, we could calculate the pentosidine formation rate constants (k(F)) for these constituents [Sivan, Tsitron, Wachtel, Roughley, Sakkee, van der Ham, DeGroot, Roberts and Maroudas (2006) J. Biol. Chem. 281, 13009-13014; Tsitron (2006) MSc Thesis, Technion-Israel Institute of Technology, Haifa, Israel]. In spite of the comparable formation rate constants obtained for A1D1 and collagen [1.81+/-0.25 compared with 3.71+/-0.26 micromol of pentosidine x (mol of lysine)(-1) x year(-1) respectively], the higher pentosidine accumulation in collagen is consistent with its slower turnover (0.005 year(-1) compared with 0.134 year(-1) for A1D1). Pentosidine accumulation increased with decreasing buoyant density and decreasing turnover of the proteins from the most glycosaminoglycan-rich PG components (A1D1) to the least (A1D6), with respective k(F) values of 1.81+/-0.25 and 3.18+/-0.37 micromol of pentosidine.(mol of lysine)(-1) x year(-1). We concluded that protein turnover is an important determinant of pentosidine accumulation in aggrecan and collagen of human IVD, as was found for articular cartilage. Correlation of pentosidine accumulation with protein half-life in both normal and degenerate discs further supports this finding.

Adult↗
PubMed2006

Aggrecan turnover in human intervertebral disc as determined by the racemization of aspartic acid.

We have used the racemization of aspartic acid as a marker for the "molecular age" of aggrecan components of the human intervertebral disc matrix (aggregating and non-aggregating proteoglycans as well as the different buoyant density fractions of aggrecan). By measuring the D/L(Asp) ratio of the various aggrecan species as a function of age and using the values of the racemization constant, k(i), found earlier for aggrecan in articular cartilage, we were able to establish directly the relative residence time of these molecules in human intervertebral disc matrix. For A1 preparations taken from normal tissue, turnover rates of 0.059 +/- 0.01 and 0.063 +/- 0.01/year correspond to half-life values of 12 +/- 2.0 and 11.23 +/- 1.9 years for nucleus pulposus and annulus fibrosus, respectively; the turnover rates of 0.084 +/- 0.022 and 0.092 +/- 0.034/year for degenerate tissue correspond to half-life values of 8.77 +/- 2.2 and 8.41 +/- 2.8 years, suggesting increased rate of removal of small aggrecan fragments. For the large monomer, fraction A1D1, turnover is 0.13 +/- 0.04/year, corresponding to a half-life of 5.56 +/- 1.58 years, similar to 3.4 years in human articular cartilage. For the binding region (A1D6), turnover is 0.033 +/- 0.0012/year, corresponding to a half-life of 21.53 +/- 0.6 years, similar to 23.5 years in articular cartilage. A1 preparations from nucleus pulposus contain a lower proportion of aggregating proteoglycans as compared with annulus fibrosus, suggesting increased proteolytic modification in the nucleus pulposus. D/L(Asp) values in aggregating and non-aggregating proteoglycans of a 24-year-old individual show similar results, suggesting that the non-aggregating molecules are synthesized initially as aggregating proteoglycans, which thereafter undergo cleavage and detachment from hyaluronan.

Adolescent↗
PubMed2006

A product of ozonolysis of cholesterol alters the biophysical properties of phosphatidylethanolamine membranes.

There is evidence that some products of the reaction of ozone with cholesterol contribute to atherosclerosis. One of these compounds is 3beta-hydroxy-5-oxo-5,6-secocholestan-6-al. We have synthesized this compound and have demonstrated that it reacts with phosphatidylethanolamine to form a Schiff base. The 3beta-hydroxy-5-oxo-5,6-secocholestan-6-al also affects the physical properties of phosphatidylethanolamines. We show by both DSC and X-ray diffraction that it increases the negative curvature of the membrane. In addition, 3beta-hydroxy-5-oxo-5,6-secocholestan-6-al causes the lamellar phase to become disorganized, resulting in the loss of lamellar periodicity. The chemical and physical interactions of 3beta-hydroxy-5-oxo-5,6-secocholestan-6-al with phosphatidylethanolamines may contribute to damaging effects of this lipid on cell membranes, resulting in pathology.

Calorimetry, Differential Scanning↗
PubMed2006

Correlation of swelling pressure and intrafibrillar water in young and aged human intervertebral discs.

Fluid balance in the intervertebral disc under applied load is determined primarily by its swelling pressure, that is, the external pressure at which it neither loses nor gains water. This depends on the composition of the tissue, in particular on its proteoglycan concentration. Proteoglycans develop a high osmotic pressure due to their fixed negatively charged groups. Because of their size, proteoglycans are excluded from the collagen's intrafibrillar volume; hence their osmotic activity is determined only by the extrafibrillar water. Here, we show that in order to evaluate correctly the swelling pressure in the annuli fibrosi of human intervertebral disc, it is essential to evaluate its proportion of intrafibrillar water. We used low-angle X-ray scattering and osmotic stress techniques to determine the lateral packing of the collagen molecules in the fibrils of the annuli fibrosi (ages: 25-77). It was found that the lateral packing and, hence, the intrafibrillar water content depends on age, external osmotic pressure, and location in the tissue. Subtracting intrafibrillar water from total hydration yields the amount of extrafibrillar water, from which the true fixed charge density of the tissue could be estimated. From a force balance, it would appear that collagen tension plays only a minor role in the equilibrium of the human intervertebral disc under load, in contrast to articular cartilage, where collagen tension is important for load bearing.

Adult↗
PubMed2005

Phosphatidylcholine structure determines cholesterol solubility and lipid polymorphism.

In the present work, we demonstrate that phosphatidylcholine with (16:1)9 acyl chains undergoes polymorphic rearrangements in mixtures with 0.6-0.8 mol fraction cholesterol. Studies were performed using differential scanning calorimetry, X-ray diffraction, cryo-electron microscopy, 31P NMR static powder patterns and 13C MAS/NMR. Mixtures of phosphatidylcholine with (16:1)9 acyl chains and 0.6 mol fraction cholesterol, after being heated to 100 degrees C, can form an ordered array with periodicity 14 nm which may be indicative of a cubic phase. Our results indicate that the formation of highly curved bilayer structures, such as those required for membrane fusion, can occur in mixtures of cholesterol with certain phosphatidylcholines that do not form non-lamellar structures in the absence of cholesterol. We also determine the polymorphic behavior of mixtures of symmetric phosphatidylcholines with cholesterol. Species of phosphatidylcholine with (20:1)11, (22:1)13 or (24:1)15 acyl chains in mixtures with 0.6-0.8 mol fraction cholesterol undergo a transition to the hexagonal phase at temperatures 70-80 degrees C. This is not the case for phosphatidylcholine with (18:1)6 acyl chains which remains in the lamellar phase up to 100 degrees C when mixed with as much as 0.8 mol fraction cholesterol. Thus, the polymorphic behavior of mixtures of phosphatidylcholine and cholesterol is not uncommon and is dependent on the intrinsic curvature of the phospholipid. Crystals of cholesterol can be detected in mixtures of all of these phosphatidylcholines at sufficiently high cholesterol mole fraction. What is unusual about the formation of these crystals in several cases is that cholesterol crystals are present in the monohydrate form in preference to the anhydrous form. Furthermore, after heating to 100 degrees C and recooling, the cholesterol crystals are again observed to be in the monohydrate form, although pure cholesterol crystals require many hours to rehydrate after being heated to 100 degrees C. Both the nature of the acyl chain as well as the mole fraction cholesterol determine whether cholesterol crystals in mixtures with the phospholipids will be in the monohydrate or in the anhydrous form.

Cholesterol↗
PubMed2004

Phase separation of cholesterol from phosphatidylserine-cholesterol mixtures in the presence of the local anesthetic tetracaine.

Addition of the local anesthetic tetracaine (TTC) to multilamellar dispersions of natural phosphatidylserine (PS) causes changes in the thermotropic properties of the membrane, which can be detected by differential scanning calorimetry, and in the structure of the membrane as detected by X-ray diffraction. At molar ratio [PS]/ [TTC] approximately 8.5, the melting temperature of the phospholipid shifts downwards by approximately 2.5 degrees C. The melting endotherm is broadened; however, there is little change in the enthalpy of melting. In ternary mixtures (PS-TTC-cholesterol), the thermotropic changes are enhanced. At [PS]/ [TTC] approximately 13, the onset of phase separation of cholesterol crystals from PS in the liquid crystalline state occurs at molar fraction cholesterol (Xchol) approximately 0.28, marginally smaller than that found in the absence of the anesthetic.

Anesthetics, Local↗
PubMed2003

Novel properties of cholesterol-dioleoylphosphatidylcholine mixtures.

We have studied the properties of mixtures of cholesterol with dioleoylphosphatidylcholine (DOPC), and with several other phospholipids, including 1-stearoyl-2-oleoylphosphatidylcholine (SOPC) and dioleoleoylphosphatidylserine (DOPS), as a function of cholesterol molar fraction and of temperature. Mixtures of DOPC with a cholesterol molar fraction of 0.4 or greater display polymorphic behavior. This polymorphism includes the formation of structures that give rise to isotropic peaks in 31P NMR at cholesterol molar fractions between 0.4 and 0.6, dependent on the thermal history of the sample. Cryo-electron microscopy studies demonstrate the formation of small globular aggregates that would contribute to a narrowing of the 31P NMR powder pattern. At molar fraction cholesterol 0.6 and higher and at temperatures above 70 degrees C, the mixtures with DOPC convert to the hexagonal phase. Lipid polymorphism is accompanied by the phase separation of cholesterol crystals in the anhydrous form and/or the monohydrate form. The crystals that are formed have substantially altered kinetics of hydration and dehydration, compared with both pure cholesterol monohydrate crystals and with crystals formed in the presence of the other phospholipids that do not form the hexagonal phase in the presence of cholesterol. This fact demonstrates that these cholesterol crystals are in intimate contact with the DOPC phospholipid and are not present as morphologically separate structures.

Calorimetry, Differential Scanning↗
PubMed2003

Phospholipid/cholesterol model membranes: formation of cholesterol crystallites.

Experimental data that define conditions under which cholesterol crystallites form in cholesterol/phospholipid model membranes are reviewed. Structural features of the phospholipids that determine cholesterol crystallization include the length and degree of unsaturation of the acyl chains, the presence of charge on the headgroups and interheadgroup hydrogen bonds.

Calorimetry, Differential Scanning↗
PubMed2003

Biomimetic lipid/polymer colorimetric membranes: molecular and cooperative properties.

Characterization of membranes and of biological processes occurring within membranes is essential for understanding fundamental cellular behavior. Here we present a detailed biophysical study of a recently developed colorimetric biomimetic membrane assembly constructed from physiological lipid molecules and conjugated polydiacetylene. Various analytical techniques have been applied to characterize the organization of the lipid components in the chromatic vesicles and their contributions to the observed blue-to-red color transitions. Experiments reveal that both the polymerized units as well as the lipids exhibit microscopic phases and form domains whose properties and bilayer organization are interdependent. These domains are interspersed within mixed lipid/polymer vesicles that have a size distribution different from those of aggregates of the individual molecular constituents. The finding that fluidity changes induced within the lipid domains are correlated with the chromatic transitions demonstrates that the colorimetric platform can be used to evaluate the effects of individual molecular components, such as negatively charged lipids and cholesterol, upon membrane fluidity and thermal stability.

Acetylene↗
PubMed2002

Alkali metal intercalated fullerene-like MS(2) (M = W, Mo) nanoparticles and their properties.

Layered metal disulfides-MS(2) (M = Mo, W) in the form of fullerene-like nanoparticles and in the form of platelets (crystallites of the 2H polytype) have been intercalated by exposure to alkali metal (potassium and sodium) vapor using a two-zone transport method. The composition of the intercalated systems was established using X-ray energy dispersive spectrometer and X-ray photoelectron spectroscopy (XPS). The alkali metal concentration in the host lattice was found to depend on the kind of sample and the experimental conditions. Furthermore, an inhomogeneity of the intercalated samples was observed. The product consisted of both nonintercalated and intercalated phases. X-ray diffraction analysis and transmission electron microscopy of the samples, which were not exposed to the ambient atmosphere, showed that they suffered little change in their lattice parameters. On the other hand, after exposure to ambient atmosphere, substantial increase in the interplanar spacing (3-5 A) was observed for the intercalated phases. Insertion of one to two water molecules per intercalated metal atom was suggested as a possible explanation for this large expansion along the c-axis. Deintercalation of the hydrated alkali atoms and restacking of the MS(2) layers was observed in all the samples after prolonged exposure to the atmosphere. Electric field induced deintercalation of the alkali metal atoms from the host lattice was also observed by means of the XPS technique. Magnetic moment measurements for all the samples indicate a diamagnetic to paramagnetic transition after intercalation. Measurements of the transport properties reveal a semiconductor to metal transition for the heavily K intercalated 2H-MoS(2). Other samples show several orders of magnitude decrease in resistivity and two- to five-fold decrease in activation energies upon intercalation. These modifications are believed to occur via charge transfer from the alkali metal to the conduction band of the host lattice. Recovery of the pristine compound properties (diamagnetism and semiconductivity) was observed as a result of deintercalation.

Journal Article↗
PubMed2002

Preparation of amorphous aluminum oxide-hydroxide nanoparticles in amphiphilic silicone-based copolymer microemulsions.

Organo-inorgano nanocomposites with colloidal dimensions have interesting optical, catalytic, and mechanical properties, particularly when such hybrids are reinforced with transition metal oxide nanoparticles. Nanoparticles with a mean size of 1.0-2.4 nm are obtained through hydrolysis of aluminum isopropoxide in the L(2) phase of amphiphilic (PDMS-POE) polydimethylsiloxane-polyoxyethylene Silwet L-7607-octanol/acetylacetone-water mixtures. The particle sizes are related weakly to the microemulsion composition: 0.8-1.2 nm for 20 wt% Silwet L-7607 and 2.0-2.4 nm for 50 wt% Silwet L-7607. Protection of the particles against aggregation is ensured through their confinement in the intraaggregate colloidal domains. Factors affecting the hydrolysis-condensation process of acetylacetone-complexed aluminum isopropoxide in copolymer-poor and copolymer-rich regions of PDMS-POE W/O microemulsions are studied by Fourier transform infrared spectroscopy, small angle X-ray scattering, and transmission electron microscopy. Prepared nanoparticulate dispersions possess long-term stability and form clear mixtures in different organic polar and nonpolar solvents.

Journal Article↗
PubMed2002

Properties of mixtures of cholesterol with phosphatidylcholine or with phosphatidylserine studied by (13)C magic angle spinning nuclear magnetic resonance.

The behavior of cholesterol is different in mixtures with phosphatidylcholine as compared with phosphatidylserine. In (13)C cross polarization/magic angle spinning nuclear magnetic resonance spectra, resonance peaks of the vinylic carbons of cholesterol are a doublet in samples containing 0.3 or 0.5 mol fraction cholesterol with 1-palmitoyl-2-oleoyl phosphatidylserine (POPS) or in cholesterol monohydrate crystals, but a singlet with mixtures of cholesterol and 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC). At these molar fractions of cholesterol with POPS, resonances of the C-18 of cholesterol appear at the same chemical shifts as in pure cholesterol monohydrate crystals. These resonances do not appear in samples of POPS with 0.2 mol fraction cholesterol or with POPC up to 0.5 mol fraction cholesterol. In addition, there is another resonance from the cholesterol C18 that appears in all of the mixtures of phospholipid and cholesterol but not in pure cholesterol monohydrate crystals. Using direct polarization, the fraction of cholesterol present as crystallites in POPS with 0.5 mol fraction cholesterol is found to be 80%, whereas with the same mol fraction of cholesterol and POPC none of the cholesterol is crystalline. After many hours of incubation, cholesterol monohydrate crystals in POPS undergo a change that results in an increase in the intensity of certain resonances of cholesterol monohydrate in (13)C cross polarization/magic angle spinning nuclear magnetic resonance, indicating a rigidification of the C and D rings of cholesterol but not other regions of the molecule.

Biophysical Phenomena↗