Chain dynamics of human dermis by Thermostimulated currents: A tool for new markers of aging.

BACKGROUND/PURPOSE: The purpose of this clinical study was to identify dielectric markers to complete a previous thermal and vibrational study on the molecular and organizational changes in human dermis during intrinsic and extrinsic aging. METHODS: Sun-exposed and non-exposed skin biopsies were collected from 28 women devised in two groups (20-30 and ≥60 years old). The dielectric relaxation modes associated with localized and delocalized dynamics in the fresh and dehydrated state were determined by the Thermostimulated currents technique (TSC). RESULTS: Intrinsic and extrinsic aging induced significant evolution of some of the dielectric parameters of localized and delocalized dynamics of human skin. With photo-aging, freezable water forms a segregated phase in dermis and its dynamics is close to free water, what evidences the major role of extrinsic aging on water organization in human skin. Moreover, TSC indicators highlight the restriction of localized mobility with intrinsic aging due to glycation, and the cumulative effect of chronological aging and photo-exposition on the molecular mobility of the main structural proteins of the dermis at the mesoscopic scale. CONCLUSION: TSC is a well-suited technique to scan the molecular mobility of human skin. It can be uses as a relevant complement of vibrational and thermal characterization to follow human skin modifications with intrinsic and extrinsic aging.

Conformational and thermal characterization of left ventricle remodeling post-myocardial infarction.

Adverse cardiac remodeling after myocardial infarction (MI) causes impaired ventricular function and heart failure. Histopathological characterization is commonly used to detect the location, size and shape of MI sites. However, the information about chemical composition, physical structure and molecular mobility of peri- and infarct zones post-MI is rather limited. The main objective of this work was to explore the spatiotemporal biochemical and biophysical alterations of key cardiac components post-MI. The FTIR spectra of healthy and remote myocardial tissue shows amides A, I, II and III associated with proteins in freeze-died tissue as major absorptions bands. In infarcted myocardium, the spectrum of these main absorptions was deeply altered. FITR evidenced an increase of the amide A band and the distinct feature of the collagen specific absorption band at 1338cm-1 in the infarct area at 21days post-MI. At 21days post-MI, it also appears an important shift of amide I from 1646cm-1 to 1637cm-1 that suggests the predominance of the triple helical conformation in the proteins. The new spectra bands also indicate an increase in proteoglycans, residues of carbohydrates in proteins and polysaccharides in ischemic areas. Thermal analysis indicates a deep increase of unfreezable water/freezable water in peri- and infarcted tissues. In infarcted tissue is evidenced the impairment of myofibrillar proteins thermal profile and the emergence of a new structure. In conclusion, our results indicate a profound evolution of protein secondary structures in association with collagen deposition and reorganization of water involved in the scar maturation of peri- and infarct zones post-MI.

Identification of ageing biomarkers in human dermis biopsies by thermal analysis (DSC) combined with Fourier transform infrared spectroscopy (FTIR/ATR).

BACKGROUND/PURPOSE: The purpose of this clinical study was to identify suitable biomarkers for a better understanding of the molecular and organizational changes in human dermis during intrinsic and extrinsic ageing. METHODS: Sun-exposed and non-exposed skin biopsies were collected from twenty-eight women devised in two groups (20-30 and ≥60 years old). The hydric organization and thermal transitions were determined by Differential Scanning Calorimetry (DSC). Fourier Transform Infrared spectroscopy (FTIR) was used to identify the absorption bands of the dermis and to quantify the different absorbance ratio. RESULTS: The amounts of total, freezable and unfreezable water were determined. A significant increasing amount of freezable water is evidenced in sun-exposed area skin of aged group compared with young group (P=.0126). Another significant effect of extrinsic ageing (P=.0489) is the drastic decrease of fibrillary collagen, the main protein component of dermis. The only significant effect of intrinsic ageing (P=.0184) is an increase of the heat-stable fraction of collagens in dermis. CONCLUSION: DSC and FTIR are well-suited techniques to characterize human skin, giving accurate results with a high reproducibility. The combination of these techniques is useful for a better understanding of human skin modifications with intrinsic and extrinsic ageing.

Conformational and thermal characterization of a synthetic peptidic fragment inspired from human tropoelastin: Signature of the amyloid fibers.

OBJECTIVES: This work deals with the conformational and thermal characterization of a synthetic peptide (S4) released during the proteolysis of human tropoelastin by the matrix metalloproteinase-12 that was shown to form amyloid-like fibres under certain conditions. MATERIALS AND METHODS: S4 peptides were synthesized by solid-phase methodology and aggregated in solution at 80°C. Fourier transform-infrared spectroscopy (FT-IR) was used to access the secondary structure. Thermal characterization was performed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). RESULTS: The DSC study of the soluble linear peptide S4 in solution in TBS reveals the irreversible aggregation into amyloid fibres. FT-IR, DSC and TGA analyses performed on freeze-dried samples evidence differences between the linear peptide and its associated amyloid-like fibres, both on the conformation and the physical structure. When S4 peptides are aggregated, the prominent conformation scanned by FT-IR is the cross ß-structure, corresponding to TGA to an increase of the thermal stability. Moreover, the DSC thermograms of S4 fibres are characteristic of a highly ordered structure, in contrast to the DSC thermograms of S4 linear peptides, characteristic of an amorphous structure. Finally, the DSC analysis of differently hydrated S4 fibres brings to the fore the specific thermal answer of the wet interfaces of the cross ß-fibres. CONCLUSION: FT-IR and thermal techniques are well suited to evidence conformational and structural differences between the soluble peptide and its amyloid form.

Analysis of the molecular mobility of collagen and elastin in safe, atheromatous and aneurysmal aortas.

AIM OF THE STUDY: In this study, we propose to use a thermal technique, Differential Scanning Calorimetry (DSC) to follow the evolution of elastin and collagen in safe and pathological cardiovascular tissues. PATIENTS AND METHODS: The first part of this study deals with the analysis of the elastin network and associated proteins during ageing (from children to old persons) in aortic walls. The second part is devoted to the characterization of the collagenic phase in aneurysms. In both cases, physical data are correlated with biochemical analyses. RESULTS AND CONCLUSION: For old persons aortas with atheromatous stades, elastin and associated proteins are found to interpenetrate to form a homogenous phase. Abdominal aortic aneurysms (AAA) are characterized by structural alterations of the aortic wall resulting from the degradation of elastic fibers and an increase of collagen/elastin ratio. Notable modifications are evidenced between collagen from control tissue and collagen from AAA, particularly concerning the thermal denaturation. Biochemical and thermal results are compatible with the increase of new collagen deposition and/or impairment of the collagen phase stability in the extracellular matrix of AAAs.

Maternal dietary omega-3 deficiency worsens the deleterious effects of prenatal inflammation on the gut-brain axis in the offspring across lifetime.

Maternal immune activation (MIA) and poor maternal nutritional habits are risk factors for the occurrence of neurodevelopmental disorders (NDD). Human studies show the deleterious impact of prenatal inflammation and low n-3 polyunsaturated fatty acid (PUFA) intake on neurodevelopment with long-lasting consequences on behavior. However, the mechanisms linking maternal nutritional status to MIA are still unclear, despite their relevance to the etiology of NDD. We demonstrate here that low maternal n-3 PUFA intake worsens MIA-induced early gut dysfunction, including modification of gut microbiota composition and higher local inflammatory reactivity. These deficits correlate with alterations of microglia-neuron crosstalk pathways and have long-lasting effects, both at transcriptional and behavioral levels. This work highlights the perinatal period as a critical time window, especially regarding the role of the gut-brain axis in neurodevelopment, elucidating the link between MIA, poor nutritional habits, and NDD.

Essential omega-3 fatty acids tune microglial phagocytosis of synaptic elements in the mouse developing brain.

Omega-3 fatty acids (n-3 PUFAs) are essential for the functional maturation of the brain. Westernization of dietary habits in both developed and developing countries is accompanied by a progressive reduction in dietary intake of n-3 PUFAs. Low maternal intake of n-3 PUFAs has been linked to neurodevelopmental diseases in Humans. However, the n-3 PUFAs deficiency-mediated mechanisms affecting the development of the central nervous system are poorly understood. Active microglial engulfment of synapses regulates brain development. Impaired synaptic pruning is associated with several neurodevelopmental disorders. Here, we identify a molecular mechanism for detrimental effects of low maternal n-3 PUFA intake on hippocampal development in mice. Our results show that maternal dietary n-3 PUFA deficiency increases microglia-mediated phagocytosis of synaptic elements in the rodent developing hippocampus, partly through the activation of 12/15-lipoxygenase (LOX)/12-HETE signaling, altering neuronal morphology and affecting cognitive performance of the offspring. These findings provide a mechanistic insight into neurodevelopmental defects caused by maternal n-3 PUFAs dietary deficiency.

Dynamic mechanical properties of a biomimetic hydroxyapatite/polyamide 6,9 nanocomposite.

A biomimetic composite of nanohydroxyapatite (nHap) and semicrystalline polyamide 6,9 (PA 6,9) was synthesized by thermally induced phase separation. The nHap powder was dispersed in a polymer matrix with a low ratio ranging 1-10 wt %. The mean size of the nHap, determined by scanning electron microscopy (SEM) was approximately 100-200 nm (length), 40-60 nm (width). Physicochemical analyses were performed in order to characterize the PA 6,9 and nHap separately on the one hand, and the PA 6,9/nHap composites on the other hand. Differential scanning calorimetry (DSC) and dynamic mechanical analyses (DMA) have pointed out an optimization of the composite physical properties as a function of nHap content till a limit value of 5 wt %. Above this value, the mechanical properties decreased. Four main parameters have been found to influence the composite physical properties improvement: the fillers content, the physical structure of the polymeric matrix, the particles dispersion and the physical interaction strength between organic and inorganic phases. The dynamic mechanical properties of this biomimetic nanocomposite were compared with human cortical bone.

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.

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.

Comparison of chemical treatments on the chain dynamics and thermal stability of bovine pericardium collagen.

A new approach for the replacement of heart valves consists of obtaining an acellular matrix from animal aortic valves that performs mechanically, is nonantigenic, and is free from calcification and fibroblast proliferation. Novel biochemical treatments must be developed for this purpose. In this work, we focus on the characterization of collagen in acellular bovine cardiovascular tissues, fresh or glutaraldehyde treated, and stored in different solutions [phosphate-buffered saline (PBS), ethanol, octanol, and glutaraldehyde], to determine whether the resulting fibrous material is structurally preserved. The preservation of the triple helical structure of collagen is checked by differential scanning calorimetry (DSC), which is a well suited technique to analyze thermal transitions in proteins, such as denaturation. To get insight into the molecular dynamics of collagen in the nanometric range, we used thermally stimulated currents, a dielectric technique running at low frequency, that measure the dipolar reorientations in proteins submitted to a static electrical field. The combined use of these two techniques allowed us to evaluate the physical structure and conformation of collagen after the different chemical treatments. We have found that the glutaraldehyde treatment followed by octanol storage preserves the triple helical conformation of the polypeptidic chains of collagen, contrary to the ethanol and PBS storage that induce drastic changes in the thermal and dielectric behavior of the protein. Moreover, this particular chemical treatment stabilizes the collagen structure (shift toward high temperature of the collagen denaturation and stiffening of the chains by a cross-linking action) when compared to the control sample, and so could provide interesting fibrous material for the conception of bioprosthetic heart valve.

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.

Dielectric study of the molecular mobility and the isothermal crystallization kinetics of an amorphous pharmaceutical drug substance.

During the development of new pharmaceutical products based on drug substances in their amorphous form, the molecular mobility of an amorphous active ingredient was characterized in detail within a very broad time-temperature range. The relation between the isothermal crystallization kinetics and the dynamics of this amorphous substance was investigated. First, dynamic dielectric spectroscopy (DDS) and the thermostimulated current (TSC) techniques were used to analyze the molecular mobility of the amorphous drug substance over a wide frequency and temperature range (the drug substance is referred to as SSR in this text and was chosen as a model glass-forming system). Two relaxation processes, corresponding to different molecular motions, were identified. The beta(a)-relaxation process, associated with intramolecular oscillation of small dipolar groups, followed Arrhenius temperature behavior over the entire time-temperature domain that was studied. However, the main alpha(a)-relaxation process, assigned to the dielectric manifestation of the dynamic glass transition of the amorphous phase, was described by Vogel-Fulcher-Tammann (VFT) and Arrhenius behavior above and below the glass transition temperature (T(g)) respectively. The physical meaning of these complex dynamics is explained in the context of the Adam and Gibbs (AG) model, by the temperature dependence of the size of cooperatively rearranging regions (CRR) that govern the time scale of delocalized molecular motions. The distinction between the molecular mobility and the structural relaxation of amorphous systems below T(g) is discussed. This work shows that the complementary nature of both DDS and TSC techniques is essential to directly analyze the intramolecular and molecular motions of disordered phases over a wide time-temperature range above and below the T(g). Second, real-time dielectric measurements were carried out to determine the isothermal crystallization kinetics of the SSR amorphous drug. Whatever the crystalline form obtained over time in the crystallization process, the decrease of the dielectric response of amorphous phase, which is characteristic of the isothermal crystallization, was studied to monitor the time dependence of the degree of crystallinity. The characteristic crystallization time, derived from Kohlrausch-Williams-Watt (KWW)-Avrami analyses performed at different temperatures, followed an Arrhenius temperature dependence. Behaviors specific to the molecular mobility of the amorphous drug substance were compared with the characteristic crystallization time. It was concluded that the crystal growth process of the SSR drug seems to be controlled by the intramolecular motions involving the beta(a)-relaxation mode and not by the molecular motions responsible for the alpha(a)-relaxation mode in the range of temperatures >T(g). Subsequent studies will focus on the crystallization process of the SSR drug in the glassy state (T < T(g)).

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.

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.

Dynamic mechanical properties of oral mucosa: Comparison with polymeric soft denture liners.

The purpose of this work was to characterize the viscoelastic behaviour of oral mucosa and compare it with the dynamic mechanical properties of different soft liners. For this purpose, a sample of pig oral mucosa and six commercialized soft liner samples have been investigated. A comparison was also carried with the first suitable hard rubber for dental prosthetics: vulcanite. Creep recovery (CR) and dynamic mechanical analysis (DMA) have been used to determine the mechanical modulus of oral mucosa and soft liners respectively. The Poisson ratio is used to compare mucosa bulk modulus and soft liner shear modulus. The biomechanical concept of conventional complete dentures needs a good adjustment of dynamic mechanical impedance between the base and oral mucosa. The viscoelastic mechanical property of the oral mucosa as a referent biopolymer has been confirmed in vitro. The modulus value, adjusted for old patients in physiological conditions, is in the order of 3 MPa. This study underlines the plasticization effect of absorbed water on the mechanical properties of the underlying tissue. This study allows us to define some characteristics of the most adapted biomaterial according to the clinical exigency. The required biomaterial must display the following properties: compatibility and chemical resistance with biological environment perpetuated mechanical properties during physiological conditions and clinical use, good adjustment of dynamic mechanical impedance with supporting mucosa and easy sample processing.

Human tropoelastin sequence: dynamics of polypeptide coded by exon 6 in solution.

Calorimetric studies were performed on exon 6 in powdered form and in solution [water and 2,2,2-trifluoroethanol (TFE), a structure-inducing solvent or cosolvent]. Dynamic dielectric spectroscopy (DDS) analyses were realized in water and 20% TFE. The major role of solvent-peptide organization is evidenced with these techniques. Calorimetric measurements reveal the structural water organization around the polypeptide as well as the presence of hydrophobic interactions in TFE solution. Dielectric measurements showed for exon 6/water a decrease of relaxations times of bulk solvent implying a faster dynamics with a slight increase of the activation entropy, suggesting that exon 6 probably creates disorder within the solvent. For TFE/water mixtures, an influence of exon 6 on its environment was seen with a relaxation associated with the exon 6/solvent interactions reinforced by storage of 72 h. Finally, exon 6/solvent interactions were clearly observed with addition of TFE.

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.