Determination of secondary structure of normal fibrin from human peripheral blood

Development of in situ forming autologous fibrin scaffold incorporating synthetic teriparatide peptide for bone tissue engineering

INTRODUCTION

This study investigates the potential of an in-situ forming scaffold using a fibrin-based scaffold derived from autologous plasma combined with Synthetic Teriparatide (TP) for bone regeneration application. TP is known for its bone formation stimulation but has limited clinical use due to side effects. This autologous delivery system aims to provide precise, controlled, localized, and long-term release of TP for accelerating bone regeneration.

METHODS

Fibrinogen from autologous plasma was extracted using ethanol, and thrombin was precipitated with ammonium sulfate to create the fibrin scaffold. Characterization of fibrinogen was done through FTIR, SDS-Page, porosity, SEM, degradation, and rheology tests. Viability was assessed by MTT in five groups with different concentrations of TP in fibrin scaffold (50, 100, and 150 µl/ml), fibrin alone, and a control group against HEK and Wharton's jelly cells. The release profile of different concentrations of TP in the fibrin scaffold was also examined.

RESULTS

The formation time of the fibrin scaffold was 4 ± 0.2 s. The highest Infrared absorption for fibrinogen was confirmed. Rheology assessment revealed a higher elastic modulus than the viscous modulus. The created fibrin scaffold displayed a consistent three-dimensional microstructure with an interconnected porous network. Cytotoxicity assays demonstrated good biocompatibility and enhanced cell growth with different concentrations of TP in the fibrin scaffold. The TP release increased with higher concentrations, peaking at an average of 61% over 54 h.

CONCLUSION

Autologous plasma-derived fibrin scaffolds incorporating TP exhibit satisfactory release within the scaffold and hold promise as a versatile bone filler for clinical use, facilitating osteoregeneration.

Biocompatible Short-Peptides Fibrin Co-assembled Hydrogels

Fibrin hydrogels made by self-assembly of fibrinogen obtained from human plasma have shown excellent biocompatible and biodegradable properties and are widely used in regenerative medicine. The fibrinogen self-assembly process can be triggered under physiological conditions by the action of thrombin, allowing the injection of pregel mixtures that have been used as cell carriers, wound-healing systems, and bio-adhesives. However, access to fibrinogen from human plasma is expensive and fibrin gels have limited mechanical properties, which make them unsuitable for certain applications. One solution to these problems is to obtain composite gels made of fibrin and other polymeric compounds that improve their mechanical properties and usage. Herein, we prepared composite hydrogels made by the self-assembly of fibrinogen together with Fmoc-FF (Fmoc-diphenylalanine) and Fmoc-RGD (Fmoc-arginine-glycine-aspartic acid). We have shown that the mixture of these three peptides co-assembles and gives rise to a unique type of supramolecular fiber, whose morphology and mechanical properties can be modulated. We have carried out a complete characterization of these materials from chemical, physical, and biological points of view. Composite gels have improved mechanical properties compared to pure fibrin gels, as well as showing excellent biocompatibility ex vivo. In vivo experiments have shown that these gels do not cause any type of inflammatory response or tissue damage and are completely resorbed in short time, which would enable their use as vehicles for cell, drug, or growth factor release.

Modification of protein secondary structure as an indicator of radiation-induced abscopal effect: A spectroscopic investigation

In this study, we investigate the abscopal effect induced in the brain, lung and kidney as a result of partial irradiation of experimental animals with 2 Gy γ-rays. Modifications in the protein secondary structure were used as indicator for the abscopal effect. FTIR spectroscopy and analysis of the amide I and amide II absorption bands suggested possible modifications in the protein secondary structure in the brain and kidney following irradiation. Significant shift in the amide I band was recorded only in the brain. However, the amide I/amide II band area ratio for the three organs examined varied differentially in the irradiated groups as compared with the sham-irradiated group. Employing the lorentzian model to analyze the amide I band of the FTIR spectra, we dissected the amide I band into its components, each component represents one form of the protein secondary structure. Calculation of the weight percentage contribution of each of the protein secondary structure revealed decrease in the α-helix contribution associated with equivalent increase in β-sheets and turns/random coils contributions in the brain and kidney, however the response was more evident in the brain. No change in the α-helix or β-sheets contributions was reported in the lung following irradiation. The data suggest the induction of abscopal effect in the brain and kidney rather than the lung in the form of protein conformation modification. The data also indicate that the abscopal effect is comparable to the effect of direct irradiation in both of the brain and kidney.

Three dimensional porous scaffolds derived from collagen, elastin and fibrin proteins orchestrate adipose tissue regeneration

Current gold standard to treat soft tissue injuries caused by trauma and pathological condition are autografts and off the shelf fillers, but they have inherent weaknesses like donor site morbidity, immuno-compatibility and graft failure. To overcome these limitations, tissue-engineered polymers are seeded with stem cells to improve the potential to restore tissue function. However, their interaction with native tissue is poorly understood so far. To study these interactions and improve outcomes, we have fabricated scaffolds from natural polymers (collagen, fibrin and elastin) by custom-designed processes and their material properties such as surface morphology, swelling, wettability and chemical cross-linking ability were characterised. By using 3D scaffolds, we comprehensive assessed survival, proliferation and phenotype of adipose-derived stem cells in vitro. In vivo, scaffolds were seeded with adipose-derived stem cells and implanted in a rodent model, with X-ray microtomography, histology and immunohistochemistry as read-outs. Collagen-based materials showed higher cell adhesion and proliferation in vitro as well as higher adipogenic properties in vivo. In contrast, fibrin demonstrated poor cellular and adipogenesis properties but higher angiogenesis. Elastin formed the most porous scaffold, with cells displaying a non-aggregated morphology in vitro while in vivo elastin was the most degraded scaffold. These findings of how polymers present in the natural polymers mimicking ECM and seeded with stem cells affect adipogenesis in vitro and in vivo can open avenues to design 3D grafts for soft tissue repair.

Controlling the Multiscale Structure of Nanofibrous Fibrinogen Scaffolds for Wound Healing

As a key player in blood coagulation and tissue repair, fibrinogen has gained increasing attention to develop nanofibrous biomaterial scaffolds for wound healing. Current techniques to prepare protein nanofibers, like electrospinning or extrusion, are known to induce lasting changes in the protein conformation. Often, such secondary changes are associated with amyloid transitions, which can evoke unwanted disease mechanisms. Starting from our recently introduced technique to self-assemble fibrinogen scaffolds in physiological salt buffers, we here investigated the morphology and secondary structure of our novel fibrinogen nanofibers. Aiming at optimum self-assembly conditions for wound healing scaffolds, we studied the influence of fibrinogen concentration and pH on the protein conformation. Using circular dichroism and Fourier-transform infrared spectroscopy, we observed partial transitions from α-helical structures to β-strands upon fiber formation. Interestingly, a staining with thioflavin T revealed that this conformational transition was not associated with any amyloid formation. Toward novel scaffolds for wound healing, which are stable in aqueous environment, we also introduced cross-linking of fibrinogen scaffolds in formaldehyde vapor. This treatment allowed us to maintain the nanofibrous morphology while the conformation of fibrinogen nanofibers was redeveloped toward a more native state after rehydration. Altogether, self-assembled fibrinogen scaffolds are excellent candidates for novel wound healing systems since their multiscale structures can be well controlled without inducing any pathogenic amyloid transitions.

Microscale spatial heterogeneity of protein structural transitions in fibrin matrices

Following an injury, a blood clot must form at the wound site to stop bleeding before skin repair can occur. Blood clots must satisfy a unique set of material requirements; they need to be sufficiently strong to resist pressure from the arterial blood flow but must be highly flexible to support large strains associated with tissue movement around the wound. These combined properties are enabled by a fibrous matrix consisting of the protein fibrin. Fibrin hydrogels can support large macroscopic strains owing to the unfolding transition of α-helical fibril structures to β sheets at the molecular level, among other reasons. Imaging protein secondary structure on the submicrometer length scale, we reveal that another length scale is relevant for fibrin function. We observe that the protein polymorphism in the gel becomes spatially heterogeneous on a micrometer length scale with increasing tensile strain, directly showing load-bearing inhomogeneity and nonaffinity. Supramolecular structural features in the hydrogel observed under strain indicate that a uniform fibrin hydrogel develops a composite-like microstructure in tension, even in the absence of cellular inclusions.

Neurodegenerative disorders: dysregulation of a carefully maintained balance?

The aggregation of misfolded proteins has long been regarded as a pathological event in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease and Huntington's disease. However, the exact molecular mechanisms that govern protein metabolism that may lead to toxicity remain largely unclear. Originally targeted as the causative agent, it has since become evident that aggregation formation may not be necessary for disease progression and studies show that they may even serve functional and protective roles. Although the focus has since shifted to the toxicity of intermediate protein species preceding aggregation formation, many questions remain: Is the blame for the neural destruction to be put on one event alone, or rather on a state of cellular disequilibrium resulting from multiple events? If the cause is multifactorial, then what triggers the toxic cascade and how can this be targeted therapeutically? In order to understand the origin of toxicity, the exact underlying mechanism and impact of each contributing process must be assessed. Therefore, the structural properties, mechanism of formation, cytotoxic and/or protective effects, as well as the clinical impact of protein intermediates and aggregates will be reviewed here with the goal to establish a neurodegenerative disease model aimed at improving current therapeutics, which may ultimately contribute towards improved treatment modalities.

Raman spectroscopy enables noninvasive biochemical characterization and identification of the stage of healing of a wound

Accurate and rapid assessment of the healing status of a wound in a simple and noninvasive manner would enable clinicians to diagnose wounds in real time and promptly adjust treatments to hasten the resolution of nonhealing wounds. Histologic and biochemical characterization of biopsied wound tissue, which is currently the only reliable method for wound assessment, is invasive, complex to interpret, and slow. Here we demonstrate the use of Raman microspectroscopy coupled with multivariate spectral analysis as a simple, noninvasive method to biochemically characterize healing wounds in mice and to accurately identify different phases of healing of wounds at different time-points. Raman spectra were collected from "splinted" full thickness dermal wounds in mice at 4 time-points (0, 1, 5, and 7 days) corresponding to different phases of wound healing, as verified by histopathology. Spectra were deconvolved using multivariate factor analysis (MFA) into 3 "factor score spectra" (that act as spectral signatures for different stages of healing) that were successfully correlated with spectra of prominent pure wound bed constituents (i.e., collagen, lipids, fibrin, fibronectin, etc.) using non-negative least squares (NNLS) fitting. We show that the factor loadings (weights) of spectra that belonged to wounds at different time-points provide a quantitative measure of wound healing progress in terms of key parameters such as inflammation and granulation. Wounds at similar stages of healing were characterized by clusters of loading values and slowly healing wounds among them were successfully identified as "outliers". Overall, our results demonstrate that Raman spectroscopy can be used as a noninvasive technique to provide insight into the status of normally healing and slow-to-heal wounds and that it may find use as a complementary tool for real-time, in situ biochemical characterization in wound healing studies and clinical diagnosis.

Interactions between inorganic pigments and proteinaceous binders in reference paint reconstructions

The degradation of the proteinaceous binders, ovalbumin (OVA) and casein, and their interactions with azurite (Cu(3)(CO(3))(2)(OH)(2)), calcium carbonate (CaCO(3)), hematite (Fe(2)O(3)) and red lead (Pb(3)O(4)) pigments were studied. A multi-analytical approach based on Thermogravimetric Analysis (TG), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR) and Size Exclusion Chromatography (SEC) was used. The research was carried out on a set of paint reconstructions, which were analysed before and after artificial light ageing. We highlighted that in most cases the inorganic pigments interact with both proteins by decreasing their thermal stability and their intermolecular β-sheet content, and that ageing induces aggregation. We hypothesized that pigments intercalate between protein molecules, producing a partial disruption to the protein-protein intermolecular interaction. In the case of casein, these phenomena continued during ageing. In fact, we observed a complete disappearance of intermolecular β-sheets and an increase in intramolecular β-sheets and random coil during ageing. This result is in agreement with the structural properties of casein, whose aggregation is known to be induced by hydrophobic interactions. On the other hand, in aged OVA paint replicas, we observed the formation of new intermolecular β-sheets and an increase in thermostability. In addition FTIR showed oxidation of the side chains of the aged OVA/hematite sample and aged casein pigment samples, and SEC highlighted hydrolysis phenomena in aged carbonate, azurite and red lead/OVA complexes and in aged casein/calcium carbonate and casein/azurite samples.

The α-helix to β-sheet transition in stretched and compressed hydrated fibrin clots

Fibrin is a protein polymer that forms the viscoelastic scaffold of blood clots and thrombi. Despite the critical importance of fibrin deformability for outcomes of bleeding and thrombosis, the structural origins of the clot's elasticity and plasticity remain largely unknown. However, there is substantial evidence that unfolding of fibrin is an important part of the mechanism. We used Fourier transform infrared spectroscopy to reveal force-induced changes in the secondary structure of hydrated fibrin clots made of human blood plasma in vitro. When extended or compressed, fibrin showed a shift of absorbance intensity mainly in the amide I band (1600-1700 cm(-1)) as well as in the amide II and III bands, indicating an increase of the β-sheets and a corresponding reduction of the α-helices. The structural conversions correlated directly with the strain or pressure and were partially reversible at the conditions applied. The additional absorbance observed at 1612-1624 cm(-1) was characteristic of the nascent interchain β-sheets, consistent with protein aggregation and fiber bundling during clot deformation observed using scanning electron microscopy. We conclude that under extension and/or compression an α-helix to β-sheet conversion of the coiled-coils occurs in the fibrin clot as a part of forced protein unfolding.

Functional amyloid--from bacteria to humans

Amyloid--a fibrillar, cross beta-sheet quaternary structure--was first discovered in the context of human disease and tissue damage, and was thought to always be detrimental to the host. Recent studies have identified amyloid fibers in bacteria, fungi, insects, invertebrates and humans that are functional. For example, human Pmel17 has important roles in the biosynthesis of the pigment melanin, and the factor XII protein of the hemostatic system is activated by amyloid. Functional amyloidogenesis in these systems requires tight regulation to avoid toxicity. A greater understanding of the diverse physiological applications of this fold has the potential to provide a fresh perspective for the treatment of amyloid diseases.

Adsorption of pathogenic prion protein to quartz sand

Management responses to prion diseases of cattle, deer, and elk create a significant need for safe and effective disposal of infected carcasses and other materials. Furthermore, soil may contribute to the horizontal transmission of sheep scrapie and cervid chronic wasting disease by serving as an environmental reservoirforthe infectious agent. As an initial step toward understanding prion mobility in porous materials such as soil and landfilled waste, the influence of pH and ionic strength (l) on pathogenic prion protein (PrPsc) properties (viz. aggregation state and zeta-potential) and adsorption to quartz sand was investigated. The apparent average isoelectric point of PrPsc aggregates was 4.6. PrPsc aggregate size was largest between pH 4 and 6, and increased with increasing l at pH 7. Adsorption to quartz sand was maximal near the apparent isoelectric point of PrPsc aggregates and decreased as pH either declined or increased. PrPsc adsorption increased as suspension l increased, and reached an apparent plateau at l approximately 0.1 M. While trends with pH and l in PrPsc attachment to quartz surfaces were consistent with predictions based on Born-DLVO theory, non-DLVO forces appeared to contribute to adsorption at pH 7 and 9 (l = 10 mM). Our findings suggest that disposal strategies that elevate pH (e.g., burial in lime or fly ash), may increase PrPsc mobility. Similarly, PrPsc mobility may increase as a landfill ages, due to increases in pH and decreases in l of the leachate.

Peptide Secondary Structure Folding Reaction Coordinate: Correlation between UV Raman Amide III Frequency, Ψ Ramachandran Angle, and Hydrogen Bonding

We used UV resonance Raman (UVRR) spectroscopy to quantitatively correlate the peptide bond AmIII3 frequency to its Psi Ramachandran angle and to the number and types of amide hydrogen bonds at different temperatures. This information allows us to develop a family of relationships to directly estimate the Psi Ramachandran angle from measured UVRR AmIII3 frequencies for peptide bonds (PBs) with known hydrogen bonding (HB). These relationships ignore the more modest Phi Ramachandran angle dependence and allow determination of the Psi angle with a standard error of +/-8 degrees , if the HB state of a PB is known. This is normally the case if a known secondary structure motif is studied. Further, if the HB state of a PB in water is unknown, the extreme alterations in such a state could additionally bias the Psi angle by +/-6 degrees . The resulting ability to measure Psi spectroscopically will enable new incisive protein conformational studies, especially in the field of protein folding. This is because any attempt to understand reaction mechanisms requires elucidation of the relevant reaction coordinate(s). The Psi angle is precisely the reaction coordinate that determines secondary structure changes. As shown elsewhere (Mikhonin et al. J. Am. Chem. Soc. 2005, 127, 7712), this correlation can be used to determine portions of the energy landscape along the Psi reaction coordinate.

Studies on the interaction of total saponins of panax notoginseng and human serum albumin by Fourier transform infrared spectroscopy

Total saponins of panax notoginseng (TPNS), isolated from the roots of panax notoginseng (Burk) F.H. Chen, have been considered as the main active components of San-Chi and have various therapeutical actions. Their interactions with human serum albumin have been investigated by Fourier transformed infrared spectrometry and fluorescence methods. The results showed that TPNS combined with HSA through C=O and C-N groups of polypeptide chain. The drug-protein combination caused the significant loss of alpha-helix structure and the microenvironment changes of the tyrosine residues in protein at higher drug concentration. Combining the curve-fitting results of amide I and amide III bands, the alterations of protein secondary structure after drug complexation were quantitatively determined. The alpha-helix structure has a decrease of approximately 6%, from 55 to 49% and the beta-sheet increased approximately 3%, from 23 to 26% at high drug concentration. However, no major alterations were observed for the beta-turn and random coil structures up on drug-protein binding.

Identification of beta-turn and random coil amide III infrared bands for secondary structure estimation of proteins

Fourier transform infrared spectroscopy is increasingly becoming an important method to determine secondary structure of peptides and proteins. Among the spectral regions arising out of coupled and uncoupled stretching and bending modes of amide bonds, amide I and amide III spectral bands have been found to be the most sensitive to the variations in secondary structure folding. Amide I spectral region (1700-1600 cm-1), although most commonly used primarily because of its strong signal, suffers from several limitations, including a strong interference from water vibrational band, relatively unstructured spectral contour, and overlap of revolved bands correspondingly to various secondary structures. In contrast, amide III spectral region (1350-1200 cm-1), albeit relatively weak in signals, does not have the above limitations. Easily resolved and better defined amide III bands are quite suitable for quantitative analysis of protein secondary structure. While amide III region has been successfully used for determination of alpha-helix and beta-sheets (Fu, F.-N., et al. (1994) Appl. Spectrosc. 48, 1432-1441), bands corresponding to beta-turns and random coils have not been identified, so far. In this paper, we describe, for the first time, identification of amide III bands corresponding to beta-turns and random coils by selectively enhancing random coils by treatment with a denaturing reagent, and secondary structure estimation of several proteins by using the band assignments. The assignments of spectral bands were as follows: 1330-1295 cm-1, alpha-helix; 1295-1270 cm-1, beta-turns; 1270-1250 cm-1, random coils; and 1250-1220 cm-1, beta-sheets. The estimations of secondary structural elements by the above assignments correlated quite well with secondary structure estimations from X-ray crystallography data.

Secondary structure and Ca2+-induced conformational change of calexcitin, a learning-associated protein

Calexcitin/cp20 is a low molecular weight GTP- and Ca2+-binding protein, which is phosphorylated by protein kinase C during associative learning, and reproduces many of the cellular effects of learning, such as the reduction of potassium currents in neurons. Here, the secondary structure of cloned squid calexcitin was determined by circular dichroism in aqueous solution and by Fourier transform infrared spectroscopy both in solution and on dried films. The results obtained with the two techniques are in agreement with each other and coincide with the secondary structure computed from the amino acid sequence. In solution, calexcitin is one-third in alpha-helix and one-fifth in beta-sheet. The conformation of the protein in solid state depends on the concentration of the starting solution, suggesting the occurrence of surface aggregation. The secondary structure also depends on the binding of calcium, which causes an increase in alpha-helix and a decrease in beta-sheet, as estimated by circular dichroism. The conformation of calexcitin is independent of ionic strength, and the calcium-induced structural transition is slightly inhibited by Mg2+ and low pH, while favored by high pH. The switch of calexcitin's secondary structure upon calcium binding, which was confirmed by intrinsic fluorescence spectroscopy and nondenaturing gel electrophoresis, is reversible and occurs in a physiologically meaningful range of Ca2+ concentration. The calcium-bound form is more globular than the apoprotein. Unlike other EF-hand proteins, calexcitin's overall lipophilicity is not affected by calcium binding, as assessed by hydrophobic liquid chromatography. Preliminary results from patch-clamp experiments indicated that calcium is necessary for calexcitin to inhibit potassium channels and thus to increase membrane excitability. Therefore the calcium-dependent conformational equilibrium of calexcitin could serve as a molecular switch for the short term modulation of neuronal activity following associative conditioning.