PubMed Health⌕ Search

Biomedical subjects

E Wachtel

Publications and source records attributed to E Wachtel.

At least 19 recordsLinked to original sources
PubMed2000

Effect of dehydroepiandrosterone on phosphatidylserine or phosphatidylcholine bilayers: DSC and X-ray diffraction study.

The effect of dehydroepiandrosterone (DHEA) on the thermotropic and structural properties of phosphatidylserine or phosphatidylcholine membranes was investigated by differential scanning calorimetry and X-ray diffraction. At molar fractions of sterol, X (sterol), less than approximately 0.2, DHEA interacts with both types of model membranes, depressing the melting temperature and reducing the enthalpy of melting. At higher concentrations, phase separation of DHEA occurs with appearance of crystallites of the S2 monohydrate form.

Calorimetry, Differential Scanning↗
PubMed2000

Cholesterol crystalline polymorphism and the solubility of cholesterol in phosphatidylserine.

There is a marked hysteresis between the heating and cooling polymorphic phase transition of anhydrous cholesterol. At a scan rate of 0.05 degrees C/min the difference in transition temperatures between heating and cooling scans is approximately 10 degrees C. This phenomenon also occurs with mixtures of cholesterol with phosphatidylserine and can result in an underestimation of the amount of crystalline cholesterol in a sample that has not been cooled sufficiently. With 1-palmitoyl-2-oleoyl phosphatidylserine and 1-stearoyl-2-oleoyl phosphatidylserine the cholesterol crystallites form while the lipid remains in the L(alpha) phase. Sonication of dimyristoyl phosphatidylserine with a 0.4 mol fraction cholesterol results in the loss of cholesterol crystallite diffraction, but only a partial loss of the polymorphic transition detected by calorimetry. We therefore conclude that the thermal history of the sample can have profound effects on the appearance of the polymorphic phase transition of cholesterol by differential scanning calorimetry. Depending on the morphology of the vesicles, diffraction methods may underevaluate the amount of cholesterol crystallites present.

Calorimetry, Differential Scanning↗
PubMed1998

The effects of pH and ionic strength on intrafibrillar hydration in articular cartilage.

The hydration of articular cartilage is an essential determinant of its load bearing capacity. Here we have examined the dependence of the amount of intrafibrillar water, associated with the collagen molecules in both native and PG-depleted cartilage specimens, on the pH and ionic strength of the bathing solution, in the presence and absence of an externally applied pressure. We found that high ionic strength reduces the collagen intermolecular spacing over a large pH range: this is consistent with the electrostatic nature of the interactions between the charged groups within the intrafibrillar space. We also found that as the pH is lowered from neutral to approximately 3, there is, as expected, a gradual increase in the overall positive charge of the intrafibrillar compartment. However, surprisingly, this is not accompanied by an increase in the intrafibrillar hydration; only at pH 1.8 does the amount of intrafibrillar water increase markedly. We suggest that, rather than overall intrafibrillar charge, it is specific local axial and azimuthal relationships among collagen molecules in the fibril, and more particularly, among their charged amino acid residues, that determine the intermolecular collagen spacing, and hence intrafibrillar hydration.

Adult↗
PubMed1998

Mechanical properties of the collagen network in human articular cartilage as measured by osmotic stress technique.

We have used an isotropic osmotic stress technique to assess the swelling pressures of human articular cartilage over a wide range of hydrations in order to determine from these measurements, for the first time, the tensile stress in the collagen network, Pc, as a function of hydration. Osmotic stress was applied by means of calibrated solutions of polyethylene glycol. Calculations of osmotic stress were based on the balance, at equilibrium, between the applied stress, the collagen stress, and the proteoglycan osmotic pressure, piPG, acting within the extrafibrillar matrix compartment. Pc vs hydration was determined for several normal human samples, both native and trypsin-treated, and for cartilage from one osteoarthritic (OA) joint. We found that for normal cartilage the collagen network does not become "limp" until the volume of cartilage has decreased by 20-25% of its initial value and that its contribution to the balance of forces in cartilage therefore must be taken into account over a much wider range of hydrations than was previously thought. For normal cartilage, the Pc vs hydration curves exhibit a steep increase with increasing hydration; trypsin treatment does not change their slope, showing that PG concentration does not influence the inherent stiffness of the collagen network. By contrast, the curves for OA specimens are considerably shallower and displaced to higher hydrations. Our findings thus highlight the role of the stiffness of the collagen network in limiting hydration in normal cartilage and ensuring a high PG concentration in the matrix, which is essential for effective load-bearing and is lost in OA.

Cartilage, Articular↗
PubMed1998

The effect of ethanol on the structure of phosphatidylserine bilayers.

Thermotrophic and structural effects of ethanol on phosphatidylserine (PS) membranes were investigated by differential scanning calorimetry (DSC) and X-ray diffraction. It was found that up to 15% (v/v) added ethanol, there is little change in the melting temperature of the phospholipid and no change in the interbilayer (d) spacing in the gel phase, indicating that there is no interdigitation of the hydrocarbon chains. Above the melting temperature of the phospholipid, a large decrease of the d spacing, due primarily to a decrease in the thickness of the bilayer, was found. Ethanol molecules located in the headgroup region apparently expand the area available to the headgroups with concomitant coiling of the acyl chains, resulting in marked thinning of the lipid layer.

Anesthetics, General↗
PubMed1997

Structural Polymorphism in a Four-Component Nonionic Microemulsion

The Winsor IV microemulsion system composed of octaethylene glycol mono n-dodecylether [C12(EO)8]/1-dodecane + n-pentanol (1:1 by weight)/water has been investigated at constant temperature using small angle X-ray scattering and electrical conductivity measurements. The results obtained are interpreted in terms of structural evolution of the molecular aggregates as a function of the stepwise addition of water or (oil + alcohol). The size and shape of a variety of microstructures are described: small, spherical micelles near the water corner and hexagonal and lamellar mesophases, which are oil- and alcohol-poor. Simple multishell models of these provide some insight into how dilution with water or swelling with (oil + alcohol) influences the overall symmetry of the aggregates, pentanol and dodecane partitioning, surfactant headgroup conformation, and the contribution of pentanol to oil solubilization. The previously identified "local" lamellar structure [O. Regev et al., Langmuir 12, 668 (1996)], which is a surfactant-rich and (oil + alcohol)-rich intermediate state between the W/O and O/W regions, is characterized here as a type of ordered, but highly obstructed, bicontinuous microemulsion.

Journal Article↗
PubMed1995

Age-related changes in collagen packing of human articular cartilage.

We have used X-ray scattering techniques to determine if the lateral packing of collagen molecules in the fibrils of human articular cartilage changes with age. Such changes would affect the available intrafibrillar volume and consequently the amount of intrafibrillar water. Measurements were made both in the presence and absence of compression on samples from donors aged 20 to 90 years. We find a weak though statistically significant tendency towards less dense collagen packing in native tissue as a function of age. However, the increase in packing density in response to pressure does not change with age, and the packing density in articular cartilage from which the proteoglycan molecules have been removed is similarly not age-dependent. The small increase in intrafibrillar water indicated by our data is insufficient to explain the reported increase in fibril diameter in samples from aged donors.

Adult↗
PubMed1995

Behavior of cholesterol and spin-labeled cholestane in model bile systems studied by electron spin resonance and synchrotron x-ray.

The behavior of mixed bile salt micelles consisting of sodium taurocholate, egg phosphatidylcholine, and cholesterol has been studied by ESR spin labeling and synchrotron x-ray scattering. Consistent with published phase diagrams, pure and mixed bile salt micelles have a limited capacity to incorporate and, hence, solubilize cholesterol. Excess cholesterol crystallizes out, a process that is readily detected both by ESR spin labeling using 3-doxyl-5 alpha-cholestane as a probe for cholesterol and synchrotron x-ray scattering. Both methods yield entirely consistent results. The crystallization of cholesterol from mixed bile salt micelles is indicated by the appearance of a magnetically dilute powder spectrum that is readily detected by visual inspection of the ESR spectra. Both the absence of Heissenberg spin exchange and the observation of a magnetically dilute powder spectrum provide evidence for the spin label co-crystallizing with cholesterol. In mixed bile salt micelles containing egg phosphatidylcholine, the solubility of cholesterol is increased as detected by both methods. With increasing content of phosphatidylcholine and increasing mole ratio cholesterol/phosphatidylcholine, the anisotropy of motion of the spin probe increases. The spin label 3-doxyl-5 alpha-cholestane is a useful substitute for cholesterol provided that it is used in dilute mixtures with excess cholesterol: the cholesterol/spin label mole ratio in these mixtures should be greater than 100. Despite the structural similarity between the two compounds, there are still significant differences in their physico-chemical properties. These differences come to the fore when cholesterol is totally replaced by the spin-label: 3-doxyl-5a-cholestane is significantly less soluble in bile salt and mixed bile salt micelles than cholesterol and, in contrast with cholesterol, it interacts only very weakly, if at all,with phosphatidylcholine. The potential of the ESR method for detecting cholesterol crystal growth in human bile is discussed.

Bile Acids and Salts↗
PubMed1994

Small-angle x-ray scattering study of dispersed crystals from bone and tendon.

A small-angle x-ray scattering study of dispersed crystals from rat bone and mineralized turkey tendon shows that the particles in both preparations have the same scattering behavior. The data are very similar to those reported by Fratzl et al. for intact turkey tendon and are consistent with the crystals being plate shaped. These observations have important implications for understanding both the structure and mineralization processes of these tissues.

Animals↗
PubMed1991

The induction of lamellar stacking by cholesterol in lecithin-bile salt model systems and human bile studied by synchrotron X-radiation.

Small angle X-ray scattering (SAXS) with synchroton radiation was used to investigate interactions among lipid particles in lecithin-bile salt model systems and in native gallbladder biles. In model systems in the absence of cholesterol, isotropic, continuous spectra were found, indicating the absence of periodic structures. In the presence of excess cholesterol, interaction in the form of lamellar stacking was detected by the appearance of discrete diffraction peaks. In the supersaturated cholesterol region of the commonly accepted phase diagram [1], where cholesterol crystals were expected, we found lamellar stacking. The high proportion of cholesterol to bile salts seems to be the common denominator of these models. The lamellar stacking was also found in native unprocessed bile. This effect of cholesterol on lipid structure has not been previously described. Lamellar stacking may contribute to cholesterol solubilization. Its influence on the kinetics of cholesterol crystallization is presently unknown.

Bile↗
PubMed1991

The effect of osmotic and mechanical pressures on water partitioning in articular cartilage.

X-ray diffraction measurements on native and proteoglycan-free articular cartilage have been made in order to test the dependence of the lateral packing of the collagen molecules on the osmotic pressure gradient, either naturally occurring or externally applied, between the intra- and extrafibrillar compartments. From the information on collagen packing we have been able to calculate, albeit with several assumptions, the amount of intrafibrillar water as a function of pressure. In parallel with the above measurements, we have quantitated, using serum albumin partitioning, the intrafibrillar water in proteoglycan-free cartilage, as a function of mechanically applied pressure. The results of both sets of experiments lead to the conclusion that the molecular packing density, and hence the intrafibrillar water content, are a function of the osmotic pressure difference between the extrafibrillar and intrafibrillar spaces or the equivalent mechanically applied pressure. The determination of intrafibrillar water has enabled us to calculate, from measured values of fixed charge density, the internal osmotic pressure of cartilage specimens, both in compressed and uncompressed states.

Adult↗
PubMed1991

[Relationship between insomnia and arterial hypotension].

The relations between insomnia and blood pressure were investigated in 151 patients (56 men and 95 women). It was found that 37.1% of the patients were normotensive, whereas 31.8% suffered from arterial hypertension and 31.1% from arterial hypotension. There was practically no difference between normotensives and hypertensives in respect of disturbed behavioral patterns of sleep, but an entirely different picture was presented by the arterial hypotensives. Characteristic features of hypotonic insomnias were (mostly in women) prolonged time before falling asleep, frequent awakening at night associated with tachycardia and long-lasting increased excitability, starting difficulties in the morning, depressive conditions, compulsive yawning and falling asleep during daytime, tiredness, lack of "drive" and reduced physical and mental efficiency. This pattern of signs and symptoms was enhanced by hypnotics and tranquilisers. During sleep blood pressures down to 50/35 Torr were measured. It is assumed that the low blood pressure results in hypoxic and hypoglycaemic conditions in the brain. Spontaneous awakening is considered to be an emergency reaction triggered by the deficient cerebral blood flow.

Adult↗
PubMed1990

Phospholipid lamellae are cholesterol carriers in human bile.

Cholesterol solubility and precipitation in bile are major factors in the pathogenesis of cholesterol gallstones. At present, mixed micelles and phospholipid vesicles are considered to be the only cholesterol carriers in bile. In this study we present evidence showing that phospholipid lamellae are major cholesterol carriers in human bile. Lamellae are a known aggregational form in pure phospholipid model systems. In the present study, lamellae were demonstrated by electron microscopy after negative staining and by small-angle X-ray diffraction in all human gallbladder bile samples examined. During diffraction experiments, cholesterol was found to crystallize from these lamellae. Cholesterol carriers in bile were separated by high-resolution chromatography and by prolonged ultracentrifugation. Lamellae were shown to solubilize most of the biliary cholesterol; vesicles solubilized a lesser amount; while micelles solubilized only a minor portion. Our data suggest that phospholipid aggregates are the main cholesterol carriers in bile. Bile salts may control the equilibrium between the various aggregational forms of cholesterol-carrying phospholipids.

Bile↗
PubMed1989

Role of the stereochemistry of the hydroxyl group of cholesterol and the formation of nonbilayer structures in phosphatidylethanolamines.

The phase behavior of mixtures of cholesterol or epicholesterol with phosphatidylethanolamine was studied by differential scanning calorimetry and by X-ray diffraction. Discrete domains of cholesterol are detected by X-ray diffraction in the L alpha phase of phosphatidylethanolamine from egg yolk and synthetic dielaidoylphosphatidylethanolamine beginning at mole fractions of 0.35-0.4 cholesterol. Separate domains of crystalline epicholesterol can also be detected in the L alpha phase of dielaidoylphosphatidylethanolamine by X-ray diffraction at as little as 0.16 mole fraction of epicholesterol. This is a result of poor miscibility of the epicholesterol with dielaidoylphosphatidylethanolamine. Epicholesterol does not alter the L beta----L alpha transition or bilayer spacing. Epicholesterol also has little effect on the diameter of the cylinders in the hexagonal phase. Formation of the inverted hexagonal phase is facilitated by addition of small amounts of cholesterol (mole fraction less than 0.2) in both egg phosphatidylethanolamine and dielaidoylphosphatidylethanolamine. However, at higher mole fractions of cholesterol, the stability of the liquid-crystalline phase is found to increase markedly for dielaidoylphosphatidylethanolamine but not for egg phosphatidylethanolamine, indicating the importance of the structure of the acyl chains in controlling the relative stability of the lamellar and nonlamellar phases in these systems. In contrast to cholesterol, epicholesterol markedly lowers the L alpha----HII phase transition temperature at low mole fraction of sterol. This result demonstrates the importance of the orientation and motional properties of an additive in determining the L alpha----HII transition temperature.

Cholesterol↗
PubMed1989

Thermotropic properties of mixtures of negatively charged phospholipids with cholesterol in the presence and absence of Li+ or Ca2+ ions.

Mixtures of cholesterol with dipalmitoylphosphatidylserine or phosphatidic acid were investigated by differential scanning calorimetry. As in mixtures of natural phosphatidylserine with cholesterol (Bach, D. (1984) Chem. Phys. Lipids 35, 385-392), also here phase separation of cholesterol at molar ratios of 2:1 (phospholipid:cholesterol) and below is observed. The limited solubility of cholesterol in negatively charged phospholipids is found to be independent of the nature of the acyl chain residues, and independent of whether the negative charge resides on both COO- and PO- groups (as in phosphatidylserine) or on PO- only (as in phosphatidic acid). The separate cholesterol phase is also seen by DSC in mixtures of natural phosphatidylserine or phosphatidic acid with cholesterol in the presence of Ca2+; and in phosphatidylserine/cholesterol mixtures in the presence of Li+, by DSC and X-ray diffraction.

Animals↗
PubMed1989

The structure of mineralized collagen fibrils.

A new model for the structure of mineralized bone collagen is presented which is compatible with neutron diffraction, electromicroscopic, crosslinking, and composition-density data. Mineralized collagen fibrils are comprised of azimuthally oriented, flexible molecules laterally arranged on a superlattice. Four nearest neighbors are longitudinally staggered by 67 nm and two neighbors by 2* 67 nm. In early stages of mineralization the molecules are parallel to the fibril axis with an average interaxis distance of 1.8 nm. In later stages they become flexed away from the fibril axis by an anisotropic lateral compression of molecules to an interaxis distance of 1.3 nm. Three quarters of the mineral in bone is disposed within the fibrils with a symmetry and habit reflecting the above organization of the collagen molecules.

Calcification, Physiologic↗
PubMed1989

[Structural changes in the dental hard substances and jaw bones of animals due to short-duration weightlessness].

Molars, incisors and parts of corpus mandibulae from a total of 40 male, 30 female (WISTAR SPF), who were exposed for a short-time microgravity, and of their 90 d old offspring were examined. It was calculated the carbonateapatite content in the teeth and in bone in percent by infrared spectroscopy. In terms of quantitative parameters the substances of the space flight group versus the controls varied clearly. Quality and size of these changes depend from sex, investigated material and time of space flight. It can be concluded that an accommodation to the flight stress is possible without any functional disorders also in the oral system.

Animals↗