Alterations in the chain dynamics of insoluble elastin upon proteolysis by serine elastases.

The high temperature dielectric relaxations of purified and elastolized ligamentum nuchae elastin in the dry state have been investigated by thermally stimulated depolarization current spectrometry, with an equivalent frequency comprised between 10(-2) and 10(-3) Hz. A main relaxation mode, located close to 150 degrees C and attributed to the dielectric manifestation of a glass transition, is found for all samples. After decomposition by the fractional polarization method, the analysis of the high temperature mode shows the existence of two relaxation mechanisms: a cooperative one, associated with flexible zones of the protein, and an isoenthalpic one, corresponding to more ordered and constrained zones. The activation parameters of the two mechanisms are dependent on the extent of elastolysis and on the nature of enzyme (pancreatic elastase vs leukocyte elastase). Both enzymes influence the dielectric behavior of elastin in a similar way: the activation enthalpy maximum of the relaxing units located in the flexible zones, characteristic of the cooperative length, decreases with increasing hydrolysis. Moreover, the isoenthalpic mechanism becomes cooperative at the highest extent of elastolysis, which highlights release of constraints in ordered zones. Nevertheless, the differences found between the two enzymatic hydrolyses are characteristic of distinct sites of cleavage in the elastin network.

Dielectric characterization of collagen, elastin, and aortic valves in the low temperature range.

The low temperature dielectric relaxation of porcine aortic valves and its main macromolecular proteins. i.e. elastin and collagen, have been investigated in the dry state and at low levels of hydration by thermally stimulated currents spectrometry, with an equivalent frequency of 10(-3) Hz. Two secondary relaxation modes, labeled gamma and beta with increasing temperature, are found for the three materials. Since the gamma-mode is independent upon hydration while the beta-mode is strongly plasticized by water, these relaxation modes have been attributed to localized motions of the polypeptidic chains containing apolar and polar residues, respectively. The deconvolution of the beta-mode by fractional polarization gives the experimental distribution of the dielectric relaxation times of the three materials, and allows us to deduce the activation parameters of each elementary process. These analyses shows the existence of compensation phenomena between the activation parameters, implying cooperative mechanisms. The occurrence of these phenomena with their characteristic parameters are used to specify the origin of the localized relaxation modes in collagen and elastin, and to assign the specific role of each protein in the aortic valves.

Characterisation of elastin and collagen in aortic bioprostheses.

Porcine aortic valves used as cardiac valve bioprostheses are well adapted to physiological functions in the short term, but they lack long-term durability. Several multi-step extractions have been performed to obtain a perfectly acellular matrix. A new physical methodology is proposed to evaluate the resulting fibrous protein damage after biochemical extraction (TRI-COL and SDS). Thermal analysis techniques are adapted to collagen and elastin characterisation in the solid state. The aortic tissue thermal transitions are determined by differential scanning calorimetry (DSC): elastin glass transition is observed around 200 degrees C, and collagen denaturation is observed around 230 degrees C. These parameters are characteristic of the elastin network arrangement and of collagen triple-helix stability. The technique of thermostimulated currents (TSC) is well suited to specify the chain dynamics of proteins. The low-temperature relaxations observed in both collagen and elastin are associated with localised motions, whereas the high-temperature modes are attributed to more delocalized motions of the chains. Therefore TSC and DSC spectrometries allow physical parameters specific to collagen and elastin to be obtained and their interaction in aortic tissues to be determined. According to the significant evolution of these parameters on SDS samples, the destabilizing effect of this detergent is highlighted.

Thermal analysis characterization of aortic tissues for cardiac valve bioprostheses.

Two multistep extractions were achieved on porcine aortic tissues to obtain acellular matrices used for cardiac bioprostheses. The evaluation of structural modifications and the possible damage of extracellular matrix fibrous proteins were investigated by means of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Protein-water interactions and degradation temperatures were determined by TGA. DSC was used to characterize protein thermal transitions (glass transition and denaturation), which provided information on the dynamic structure of the aortic tissue components. Sodium dodecyl sulfate (SDS) extraction had a destructuring effect, while Triton and cholate treatments did not affect the structural integrity of either elastin and collagen. A DSC comparison showed that SDS destabilizes the collagen triple helical domain and swells the elastin network.

Solid-state studies on synthetic fragments and analogues of elastin.

A series of synthetic fragments and analogues of elastin have been investigated, in the solid state, by means of differential scanning calorimetry and thermally stimulated current. Most of the polypeptides were shown to possess both amorphous regions and segments of long-range order. Water, which interacts preferentially with the amorphous zones, behaves as plasticizer, i.e. facilitates the localized motions of polypeptide chains. The results obtained have been correlated with elastin elasticity, in particular as far as the fundamental destructuring role of water is concerned.

Phase transitions and chain dynamics, in the solid state, of a pentapeptide sequence of elastins.

Differential scanning calorimetry (d.s.c.) and thermally stimulated current (t.s.c.) have been applied to the study of thermal transitions and dielectric relaxations of a pentapeptide sequence: Gly-Leu-Gly-Gly-Val of elastin. The manifestation of the glass transition has been observed by both techniques. The analysis of the fine structure of t.s.c. spectra reveals the existence of local order in the amorphous phase upon physical ageing. In the 'true' amorphous phase, cooperative motions of sequences of various length are observed. The corresponding activation parameters are characteristic of the 'structure' of the amorphous phase and might be used as reference for further studies.

The effect of aluminum ions and sorbitol on collagen and skin: a thermally stimulated current spectroscopy study.

The influence of aluminum ions introduced either directly or with sorbitol, in collagen and skin, has been investigated by Thermally Stimulated Current/TSC spectroscopy. The intramolecular mobility of collagen has been found to be significantly reduced by aluminum ions. The substitution of water molecules by aluminum ions on intramolecular hydrophilic sites is suggested to be responsible for this evolution. The presence of sorbitol minimizes this effect. The intermolecular mobility of collagen is decreased upon introduction of aluminum ions in presence of sorbitol. This result can be explained by the interaction of sorbitol-aluminum entities with the telopeptidic regions of collagen molecules. In skin samples, the intra- and intermolecular mobilities are restored due to the combined actions of sorbitol and noncollagenous proteins and other macromolecules.

Study of the mineral-organic linkage in an apatitic reinforced bone cement.

In order to increase mechanical properties of surgical cements, an apatitic filler has been linked to the polymethylmethacrylate (PMMA) matrix. We report here the study of the linkage between the mineral and organic components by a dielectric spectroscopy: Thermally Stimulated Current. First, the mineral-organic interface between apatitic-octocalcic phosphate and hydroxyethylmethacrylate (HEMA) has been investigated. Second, the filler-matrix interface between grafted apatite and PMMA has been examined. It has been shown that the filler is chemically linked to the matrix and stiffens the PMMA bone cement.

Differential scanning calorimetry study of the interaction of antidepressant drugs, noradrenaline, and 5-hydroxytryptamine with a membrane model.

Differential scanning calorimetry was used to study the interaction of a membrane model with two neuromediators [noradrenaline and 5-hydroxytryptamine (Serotonin)] and four antidepressant drugs (imipramine, indalpine, citalopram, and milnacipran), known to be uptake inhibitors of these neuromediators. The study was carried out on dipalmitoyl phosphatidylcholine liposomes, a bilayer phospholipid system taken as a simplified model of biological membranes. Analysis of the thermograms led us to classify the molecules according to their lipophilic action, as in the conventional measurement of the water-octanol partition coefficient, and also enabled us to precisely determine their location along the phospholipid bilayer. A hypothesis based on this localization is put forward concerning the competitive, or otherwise, character of the blocking of uptake of the neuromediators. The extreme cases of interaction and localization of imipramine and milnacipran, a new antidepressant, relative to the bilayer are also analyzed in terms of side effects.

Characterization of interfaces in human calcified tissue.

Thermostimulated current spectroscopy has been applied to the investigation of molecular mobility in human calcified tissue. A comparative study of extracts at various stages of demineralization is presented. The response of an organic-mineral complex interphase has been identified.

Micromechanical spectroscopy of cartilage proteoglycans: hydration.

Proteoglycan subunits extracted from calf cartilage have been studied with a high resolving power mechanical spectroscopy: the Thermostimulated Creep (TSC). The influence of hydration on TSC spectra shows the existence of two types of bound water: the weakly bound water increases the inertia of proteoglycan and stiffens their structure; the strongly bound water is responsible to a compensation law indicating the existence of a resonance phenomenon at the physiological temperature. Because of the looseness of bonds in weakly bound water, an increase of the local pressure may induce, in vivo, a release of water in tissues. This hypothesis explains perfectly the role of a water pump of proteoglycans in cartilage.

[Effects of anabolics on the thermostimulated current spectrum in calf muscles]. / Effets des anabolisants sur les spectres de courants thermostimulés des muscles de veaux.

The effects of growth substances (zeranol, trenbolone) on calf muscle (pectoralis transversus) have been studied with a recent physical method (thermostimulated current spectroscopy). This method appears promising for detecting meat from calves treated with such hormonal substances. The authors have hypothesized that the observed differences are related to protein modification, the nature of which is yet unknown. A complementary work is now in progress.

Ex-vivo study of molecular interfaces in calcified tissues.

The aim of this work is the characterization of interfaces in calcified tissues. Thermally Stimulated Currents and Gel Permeation Chromatography have been used for investigating extracts and residues from calf femoral diaphysis, at various stages of demineralization. In residues, the evolution of molecular mobility shows that the organic-mineral linkage is insured by several proteins: Collagen is not directly linked to apatite.

Influence of cadmium on the chain dynamics of collagen in rat tail tendon.

The molecular mobility of the chain dynamics of collagen was investigated by the thermally stimulated creep method on rat tail tendon after oral administration of cadmium (8 mg.kg-1.day-1) for six weeks. The high resolving power of the technique shows two manifestations of the pseudolathyrogen effect of cadmium: the polar side-chains of collagen, mobile in the immature specimen, which are cross-linked and so immobile in the mature specimen, remain mobile in the cadmium-treated mature specimen. There is also a subsequent decrease in the number of water molecules linked by two hydrogen atoms bound to the tropocollagen molecules. Probably these molecular modifications inhibit mineralization of the organic matrix and so osteogenesis.

Reorientable electric dipoles and cooperative phenomena in human tooth enamel.

A preliminary investigation of electric dipole reorientability in human tooth enamel (TE) in comparison to that in hydroxyapatite (OHAp) has been made with the fractional-polarization form of the thermally stimulated currents (TSC) method. The reorientable dipoles are the structural OH-ions. The OHAp exhibited compensation phenomena at 211.5 degrees C and at 356 degrees C which are associated here with the hexagonal form becoming quasi-statically stabilized and dynamically stabilized, respectively, against the monoclinic form. TE specimens were pretreated at various temperatures. All showed the onset of cooperative motions that could quasi-statically stabilize the hexagonal form at the same temperature, approximately 212 degrees C, as did OHAp, even though the TE was already statically stabilized in the hexagonal form. Parts of the TSC spectra that did not conform to the 212 degrees C compensation changed progressively with pretreatment temperature. Loss of incorporated H2O is identified as the most probable cause of most of these changes. This work shows considerable promise for TSC as a tool for further quantitative investigation of TE.