Identification of an intermediate state in the helix-coil degradation of collagen by ultraviolet light

Fluence-dependent degradation of fibrillar type I collagen by 222 nm far-UVC radiation

For more than 100 years, germicidal lamps emitting 254 nm ultraviolet (UV) radiation have been used for drinking-water disinfection and surface sterilization. However, due to the carcinogenic nature of 254 nm UV, these lamps have been unable to be used for clinical procedures such as wound or surgical site sterilization. Recently, technical advances have facilitated a new generation of germicidal lamp whose emissions centre at 222 nm. These novel 222 nm lamps have commensurate antimicrobial properties to 254 nm lamps while producing few short- or long-term health effects in humans upon external skin exposure. However, to realize the full clinical potential of 222 nm UV, its safety upon internal tissue exposure must also be considered. Type I collagen is the most abundant structural protein in the body, where it self-assembles into fibrils which play a crucial role in connective tissue structure and function. In this work, we investigate the effect of 222 nm UV radiation on type I collagen fibrils in vitro. We show that collagen's response to irradiation with 222 nm UV is fluence-dependent, ranging from no detectable fibril damage at low fluences to complete fibril degradation and polypeptide chain scission at high fluences. However, we also show that fibril degradation is significantly attenuated by increasing collagen sample thickness. Given the low fluence threshold for bacterial inactivation and the macroscopic thickness of collagenous tissues in vivo, our results suggest a range of 222 nm UV fluences which may inactivate pathogenic bacteria without causing significant damage to fibrillar collagen. This presents an initial step toward the validation of 222 nm UV radiation for internal tissue disinfection.

3D-Printing Biodegradable PU/PAAM/Gel Hydrogel Scaffold with High Flexibility and Self-Adaptibility to Irregular Defects for Nonload-Bearing Bone Regeneration

A three-dimensional (3D) printed biodegradable hydrogel scaffold with a strong self-expanding ability to conform to the contour of irregular bone defects and be closely adjacent to host tissues is reported herein. The scaffold has a triple cross-linked network structure consisting of photo-cross-linked polyacrylamide (PAAM) and polyurethane (PU) as the primary IPN network and chemical cross-linked gelatin (Gel) as the secondary network, which confers the scaffold with good mechanical properties. The addition of PU in the polymerization process of acrylamide (AAM) can improve the ultraviolet (UV) photocuring efficiency of the hydrogel and incorporate abundant hydrogen bonds between the PAAM copolymer chain and the PU chain. The results show that the hydrogel scaffold contains regular structures with smooth morphology, excellent dimensional stability, and uniform aperture. The degradation rate of the hydrogel scaffold is controllable through adjusting cross-linking agents and can be up to about 60% after degradation for 28 days. More importantly, the rapid self-inflating characteristic of the scaffold in water, that is, the volume of hydrogel scaffold can increase to about 8 times that of their own in an hour and can generate a slight compressive stress on the surrounding host tissue, thus stimulating the reconstruction and growth of new bone tissues. The in vitro experiment indicates that the scaffold is nontoxic and biocompatible. The in vivo experiment shows that the PU/PAAM/Gel chemically cross-linked scaffold displays the desirable osteogenic capability. This UV-curable 3D printed self-adaptive and degradable hydrogel scaffold holds great potential for nonload-bearing bone repair.

The Influence of UV Light on Rheological Properties of Collagen Extracted from Silver Carp Skin

Acid soluble collagen (ASC) was extracted from Silver Carp fish skin. Collagen was dissolved in acetic acid at varying concentrations and its rheological properties were studied. Steady shear flow properties of collagen solutions at concentrations of 5 and 10 mg/mL were characterized using rheometry at 20 °C. Collagen solutions were irradiated with UV light (wavelength 254 nm) for up to 2 h and rheological properties were measured. All the collagen solutions showed a shear-thinning flow behavior. A constant viscosity region was observed after 1 h of UV irradiation, which showed that collagen molecules were fully denatured. A short treatment with collagen solution by UV (ultraviolet) light led to an increase in viscosity; however, the denaturation temperature of UV-irradiated collagen decreased. Depending on the time of UV treatment, collagen extracted from Silver Carp fish skin may undergo physical crosslinking or photodegradation. Physically crosslinked collagen may find applications in functional food, cosmetic, biomedical, and pharmaceutical industries.

UV irradiation of Type I collagen gels changed the morphology of the interconnected brain capillary endothelial cells on them

We cultured mouse brain capillary endothelial cell line bEnd.3 on the UV-irradiated Type I collagen gel. Morphology of bEnd.3 cells on the Type I collagen gel was drastically changed if the gel was crosslinked by UV irradiation. The interconnecting network of bEnd.3 cells which have cord-like morphology on the soft collagen gels was converted to the monolayer of the flat cells, tightly-bound each other covering the gel surface, in a confluent state. The collagen gels were mechanically stiffened by UV irradiation for 15 min with UV light at 254 nm showing approximately two times higher value of Young's modulus E (1.51 ± 0.58 kPa) than the control gel (3.17 ± 1.17 kPa). AFM images of the collagen fibrils were not severely changed after irradiation. Collagen subunit proteins were crosslinked and degraded simultaneously under UV irradiation proved by results of SDS-PAGE and separation by centrifugation. Expression of Integrin gene was measured by quantitative real-time PCR. Expression of the integrin α2 gene, tight junction protein 1 gene, and claudin 5 gene were down-regulated in cells on the UV irradiated collagen gel in comparison with the unirradiated one while expression of the integrin β1 gene and Integrin α1 gene did not significantly change. Thick actin filaments were more clearly observed in the cells on the UV-irradiated collagen gel than the unirradiated one by fluorescent microscopy. We conclude that UV irradiation made the collagen gel stiffened and changed the physiological state of bEnd.3 cells including their adhesion, extension, and proliferation.

Ultraviolet light (365 nm) transmission properties of articular cartilage as a function of depth, extracellular matrix, and swelling

Current tissue engineering approaches for treatment of injured or diseased articular cartilage use ultraviolet light (UV) for in situ photopolymerization of biomaterials to fill chondral and osteochondral defects as well as resurfacing, stiffening and bonding the extracellular matrix and tissue interfaces. The most commonly used UV light wavelength is UVA 365 nm, the least cytotoxic and deepest penetrating. However, little information is available on the transmission of UVA 365 nm light through the cartilage matrix. In the present study, 365 nm UV light transmission was measured as a function of depth through 100 μm thick slices of healthy articular cartilage removed from mature bovine knees. Transmission properties were measured in normal (Native) cartilage and after swelling equilibration in phosphate-buffered saline (Swollen). Single-factor and multiple linear regression analyses were performed to determine depth-dependencies between the effective attenuation coefficients and proteoglycan, collagen and water contents. For both cartilages, a significant depth-dependency was found for the effective attenuation coefficients, being highest at the articular surface (superficial zone) and decreasing with depth. The effective attenuation coefficients for full-thickness cartilages were approximately a third lower than the total attenuation coefficients calculated from the individual slices. Analysis of absorption and scattering effects due to the ECM and chondrocytes found that UV light scatter coefficients were ∼10 times greater than absorption coefficients. The greater transmittance of UV light through the thicker cartilage was attributed to the collagen within the ECM causing significant backscatter forward reflectance.

Quantification of nitrogenous bases, DNA and Collagen type I for the estimation of the postmortem interval in bone remains

Estimating the postmortem interval (PMI) is an important goal in forensic medicine and continues to be one of the most difficult tasks of the forensic investigator. Few accurate methods exist to determine the time since death of skeletonized human remains due to the great number of intrinsic and external factors that may alter the normal course of postmortem change. The purpose of this research was to assess the usefulness of various biochemical parameters, such as nitrogenous bases (adenine, guanine, purines, cytosine, thymine, pyrimidines, hypoxanthine and xanthine), DNA and Collagen Type I peptides to estimate PMI. These parameters were analysed in cortical bone for the establishment of data in a total of 80 long bones of 80 corpses (50 males, 30 females) with a mean age of 68.31 years (S.D.=18.021, range=20-97). The bones were removed from the cement niches of a cemetery in Murcia (south-eastern Spain), where they had lain for between 5 and 47 years (mean time 23.83 years, S.D.=10.85). Our results show a significant decrease in adenine (p=0.0004), guanine (p=0.0001), purines (p=0.0001), cytosine (p=0.0001), thymine (p=0.0226), pyrimidines (p=0.0002) and the number of peptides of Collagen type I (p=0.0053) in those with a PMI≥20 years. In a curvilinear regression analysis the results show that 30.6% of the variable PMI could be explained by guanine concentration, in bones with a PMI<20 years, while in cases of a PMI≥20 years, the variable that best explained membership of this group was adenine (38.0%). In the discriminant analysis applied to the all the variables as a function of PMI when two groups were established, 86.7% of the cases were correctly classified. These results show that the quantification of Collagen type I proteins and nitrogenous bases could be used as a complementary tool, together with other analyses, in the estimation of PMI.

Single-photon absorption of isolated collagen mimetic peptides and triple-helix models in the VUV-X energy range

By monitoring ionization and fragmentation after single-photon absorption, we show that an isolated collagen triple helix model is stabilized by proline hydroxylation.

A radio-theranostic nanoparticle with high specific drug loading for cancer therapy and imaging

We have developed a theranostic nanoparticle delivering the model radionuclide (177)Lu based on the versatile lipid-calcium-phosphate (LCP) nanoparticle delivery platform. Characterization of (177)Lu-LCP has shown that radionuclide loading can be increased by several orders of magnitude without affecting the encapsulation efficiency or the morphology of (177)Lu-LCP, allowing consistency during fabrication and overcoming scale-up barriers typical of nanotherapeutics. The choice of (177)Lu as a model radionuclide has allowed in vivo anticancer therapy in addition to radiographic imaging via the dual decay modes of (177)Lu. Tumor accumulation of (177)Lu-LCP was measured using both SPECT and Cerenkov imaging modalities in live mice, and treatment with just one dose of (177)Lu-LCP showed significant in vivo tumor inhibition in two subcutaneous xenograft tumor models. Microenvironment and cytotoxicity studies suggest that (177)Lu-LCP inhibits tumor growth by causing apoptotic cell death via double-stranded DNA breaks while causing a remodeling of the tumor microenvironment to a more disordered and less malignant phenotype.

Damage to skin extracellular matrix induced by UV exposure

SIGNIFICANCE

Chronic exposure to environmental ultraviolet radiation (UVR) plays a key role in both photocarcinogenesis and induction of accelerated skin aging. Although the spatiotemporal consequences of UVR exposure for the composition and architecture of the dermal extracellular matrix (ECM) are well characterized, the pathogenesis of photoaging remains poorly defined. Given the compelling evidence for the role of reactive oxygen species (ROS) as mediators of photoaging, UVR-exposed human skin may be an accessible model system in which to characterize the role of oxidative damage in both internal and external tissues.

RECENT ADVANCES

Although the cell-mediated degradation of dermal components via UVR-induced expression of ECM proteases has long been identified as an integral part of the photoaging pathway, the relative importance and identity of cellular and extracellular photosensitizers (direct hit and bystanders models, respectively) in initiating this enzymatic activity is unclear. Recently, both age-related protein glycation and relative amino-acid composition have been identified as potential risk factors for photo-ionization and/or photo-sensitization. Here, we propose a selective multi-hit model of photoaging.

CRITICAL ISSUES

Bioinformatic analyses can be employed to identify candidate UVR targets/photosensitizers, but the action of UVR on protein structure and/or ROS production should be verified experimentally. Crucially, in the case of biochemically active ECM components such as fibronectin and fibrillin, the downstream effects of photo-degradation on tissue homeostasis remain to be confirmed.

FUTURE DIRECTIONS

Both topical antioxidants and inhibitors of detrimental cell signaling may be effective in abrogating the effects of specific UVR-mediated protein degradation in the dermis.

The effects of crosslinking of scaffolds engineered from cartilage ECM on the chondrogenic differentiation of MSCs

Scaffolds fabricated from cartilage extracellular matrix provide a chondroinductive environment that stimulates cartilaginous matrix synthesis in a variety of cell types. A limitation of these cartilage-derived matrix (CDM) scaffolds is that they contract during in vitro culture, which unpredictably alters their shape. The current study examined the hypothesis that collagen crosslinking techniques could inhibit cell-mediated contraction of CDM scaffolds. We analyzed the effects of dehydrothermal (DHT) treatment, ultraviolet light irradiation (UV), and the chemical crosslinker carbodiimide (CAR) on scaffold contraction and chondrogenic differentiation of adult human bone marrow-derived stem cells (MSCs). Both physical and chemical crosslinking treatments retained the original scaffold dimensions. DHT and UV treatments produced significantly higher glycosaminoglycan and collagen contents than CAR crosslinked and non-crosslinked constructs. Crosslinking treatments influenced the composition of newly synthesized matrix, and DHT treatment best matched the composition of native cartilage. DHT, UV, and non-crosslinked CDM films supported cell attachment, while CAR crosslinking inhibited cell adhesion. These results affirm that collagen crosslinking treatments can prevent cell-mediated contraction of CDM scaffolds. Interestingly, crosslinking treatments influence chondrogenic differentiation. These effects seem to be mediated by modifications to cell-matrix interactions between MSCs and the CDM; however, further work is necessary to elucidate the specific mechanisms involved in this process.

Chemical consequences of cutaneous photoageing

Human skin, in common with other organs, ages as a consequence of the passage of time, but in areas exposed to solar ultraviolet radiation, the effects of this intrinsic ageing process are exacerbated. In particular, both the severity and speed of onset of age-related changes, such as wrinkle formation and loss of elasticity, are enhanced in photoaged (also termed extrinsically aged) as compared with aged, photoprotected, skin. The anatomy of skin is characterised by two major layers: an outer, avascular, yet highly cellular and dynamic epidermis and an underlying vascularised, comparatively static and cell-poor, dermis. The structural consequences of photoageing are mainly evident in the extracellular matrix-rich but cell-poor dermis where key extracellular matrix proteins are particularly susceptible to photodamage. Most investigations to date have concentrated on the cell as both a target for and mediator of, ultraviolet radiation-induced photoageing. As the main effectors of dermal remodelling produced by cells (extracellular proteases) generally have low substrate specificity, we recently suggested that the differential susceptibility of key extracellular matrix proteins to the processes of photoageing may be due to direct, as opposed to cell-mediated, photodamage.

In this review, we discuss the experimental evidence for ultraviolet radiation (and related reactive oxygen species)-mediated differential degradation of normally long lived dermal proteins including the fibrillar collagens, elastic fibre components, glycoproteins and proteoglycans. Whilst these components exhibit highly diverse primary and hence macro- and supra-molecular structures, we present evidence that amino acid composition alone may be a useful predictor of age-related protein degradation in both photoexposed and, as a consequence of differential oxidation sensitivity, photoprotected, tissues.

UV damage of collagen: insights from model collagen peptides

Fibrils of Type I collagen in the skin are exposed to ultraviolet (UV) light and there have been claims that collagen photo-degradation leads to wrinkles and may contribute to skin cancers. To understand the effects of UV radiation on collagen, Type I collagen solutions were exposed to the UV-C wavelength of 254 nm for defined lengths of time at 4°C. Circular dichroism (CD) experiments show that irradiation of collagen leads to high loss of triple helical content with a new lower thermal stability peak and SDS-gel electrophoresis indicates breakdown of collagen chains. To better define the effects of UV radiation on the collagen triple-helix, the studies were extended to peptides which model the collagen sequence and conformation. CD studies showed irradiation for days led to lower magnitudes of the triple-helix maximum at 225 nm and lower thermal stabilities for two peptides containing multiple Gly-Pro-Hyp triplets. In contrast, the highest radiation exposure led to little change in the T(m) values of (Gly-Pro-Pro)(10) and (Ala-Hyp-Gly)(10) , although (Gly-Pro-Pro)(10) did show a significant decrease in triple helix intensity. Mass spectroscopy indicated preferential cleavage sites within the peptides, and identification of some of the most susceptible sites of cleavage. The effect of radiation on these well defined peptides gives insight into the sequence and conformational specificity of photo-degradation of collagen.

Effect of UV irradiation on the physico-chemical properties of iron crosslinked collagen

Collagen is the main component of connective tissue and finds immense applications as a biomaterial. In this study, effect of UV irradiation on collagen crosslinked with iron has been carried out. The physical and optical properties of crosslinked collagen affected by UV irradiation were analyzed using electrospectral and fluorescence studies. The electronic spectral studies showed that the photoproducts formed on UV radiation decrease in the presence of iron. Circular dichroic studies revealed that the conformational changes brought about in the protein due to UV irradiation have been reduced owing to the crosslinking with iron. However, prolonged irradiation does bring about conformational changes to the protein.

An efficient visible light controlled protein delivery system

A visible light triggered protein delivery system has been assembled through hydroxyl coordinated onto titania nanoparticles. Biomolecules such as hemoglobin (Hb) can be controlled-released from the hybrid material TiO(2)-DB-Hb by switching visible light on/off. The released Hb not only retains its senior structure but also can fulfil the enzymatic bioactivity. Controlled delivery of Hb stems from the scission of the Ti-O coordination bond with the aid of photo-inducing electron transfer property of titania.

The use of thermal techniques for the characterization and selection of natural biomaterials

In this paper we explore the ability of thermal analysis to check elastin and collagen integrity in different biomaterial applications. Differential Scanning Calorimetry (DSC) has been used to analyze the first and second order transitions of the biological macromolecules in the hydrated and dehydrated state. First, we report the characterization of control cardiovascular tissues such as pericardium, aortic wall and valvular leaflet. Their thermal properties are compared to pure elastin and pure collagen. Second, we present results obtained on two collagen rich tissues: pericardia with different chemical treatments and collagen with physical treatments. Finally, more complex cardiovascular tissues composed of elastin and collagen are analyzed and the effect of detergent treatment on the physical structure of collagen and elastin is brought to the fore.

[Modification of collagen during action light]

In work chemical modification of collagen during action visible spectrum sunlight. These changes of collagen were found to indicate a photodegradation and photooxidation processes in collagen.

Laser-induced modification of the patellar ligament tissue: comparative study of structural and optical changes

The effects of non-ablative infrared (IR) laser treatment of collagenous tissue have been commonly interpreted in terms of collagen denaturation spread over the laser-heated tissue area. In this work, the existing model is refined to account for the recently reported laser-treated tissue heterogeneity and complex collagen degradation pattern using comprehensive optical imaging and calorimetry toolkits. Patella ligament (PL) provided a simple model of type I collagen tissue containing its full structural content from triple-helix molecules to gross architecture. PL ex vivo was subjected to IR laser treatments (laser spot, 1.6 mm) of equal dose, where the tissue temperature reached the collagen denaturation temperature of 60 ± 2°C at the laser spot epicenterin the first regime, and was limited to 67 ± 2°C in the second regime. The collagen network was analyzed versus distance from the epicenter. Experimental characterization of the collagenous tissue at all structural levels included cross-polarization optical coherence tomography, nonlinear optical microscopy, light microscopy/histology, and differential scanning calorimetry. Regressive rearrangement of the PL collagen network was found to spread well outside the laser spot epicenter (>2 mm) and was accompanied by multilevel hierarchical reorganization of collagen. Four zones of distinct optical and morphological properties were identified, all elliptical in shape, and elongated in the direction perpendicular to the PL long axis. Although the collagen transformation into a random-coil molecular structure was occasionally observed, it was mechanical integrity of the supramolecular structures that was primarily compromised. We found that the structural rearrangement of the collagen network related primarily to the heat-induced thermo-mechanical effects rather than molecular unfolding. The current body of evidence supports the notion that the supramolecular collagen structure suffered degradation of various degrees, which gave rise to the observed zonal character of the laser-treated lesion.

On the effects of UV-C and pH on the mechanical behavior, molecular conformation and cell viability of collagen-based scaffold for vascular tissue engineering

Collagen-based vascular substitutes represent in VTE a valid alternative for the replacement of diseased small-calibre blood vessels. In this study, collagen gel-based scaffolds were crosslinked combining modulation of pH and UV-C radiation. The effects on the mechanical properties, on the molecular structure and on cell viability and morphology were investigated. The mechanical response increased as a function of pH or UV-C dose and strongly depended on the test speed. Collagen molecular conformation resulted only slightly modified. While cell adhesion was not significantly altered, cell proliferation partially decreased in function of pH and UV-C. These findings suggest that UV-C treated collagen gels can represent an adequate substrate for VTE applications.

UV-vis and FT-IR spectra of ultraviolet irradiated collagen in the presence of antioxidant ascorbic acid

The influence of deleterious UV radiation on collagen molecules in the absence and presence of ascorbic acid using UV-vis and FT-IR spectroscopy has been studied. Intensity of UV-vis absorption spectrum of collagen with a maximum at 275 m due to the aromatic residues (tyrosine and phenylalanine) increases with the increasing dose of UV radiation. This effect is significantly hindered in the presence of antioxidant ascorbic acid. Intensities of FT-IR bands (amide A, B, I and II) of collagen decrease with the increase of the UV radiation dosage. Intensities of bands are also decreased in the presence of ascorbic acid. Results suggest that increasing the concentration of ascorbic acid increases the photo-stability of collagen, and the collagen becomes less sensitive to UV radiation. It is possible that hydrogen bonds form between the groups N-H of collagen and C=O of ascorbic acid. It is believed that under UV radiation free radicals appear in acid soluble collagen and resulting in photodegradation of the macromolecule restore due to the ability of ascorbic acid donating one or two electrons. Increasing the dose of radiation causes more molecules of ascorbic acid to slow down, and their antioxidant effect is diminished accordingly.

Stability of collagen in the presence of 3,4-dihydroxyphenylalanine (DOPA)

Many cross-linking agents for collagen are available with varying levels of toxicity and some are in use in biomedical implants of collagen. L-DOPA (3,4-dihydroxyphenylalanine), a neurotransmitter, is a naturally present compound in the living system and is the target in therapeutic strategy of Parkinson's disease. This work reports the effect of the neurotransmitter DOPA on the stability of collagen solution using circular dichroism (CD), fluorescence spectroscopy, melting and shrinkage temperature. Collagen solution treated with various concentrations of DOPA ranging from 10(-2) to 10(-5)M was analyzed using fluorescence and CD spectra. When collagen was treated with DOPA, the intensity of emission was found to increase indicating the possibility of interaction of DOPA with collagen and maximum emission intensity was observed between 10(-3) and 10(-4)M for L-DOPA and DL-DOPA, respectively. CD studies show possible aggregation of collagen even in the presence of low concentrations of DOPA. The shrinkage temperature of DOPA treated collagen fibres was experimentally determined to be 69+/-1 degrees C. The melting temperature of DOPA cross linked collagen solution also exhibited a significant increase from 35 to 40 degrees C (+/-0.1) (P<0.05). The experimental results suggest that the optimum concentration for cross linking collagen with DOPA ranges between 10(-3) and 10(-4)M. Thus, DOPA may be a useful stabilizing agent for collagen for biomedical applications.

Identification of free radicals induced by UV irradiation in collagen water solutions

Electron paramagnetic resonance (EPR) method has shown that hydrogen atoms and acetic acid free radicals appear in surrounding acetic acid-water solution of collagen under ultraviolet (UV) irradiation. These free radicals interact with the collagen molecule; consequently, seven superfine components of EPR spectrum with the split of aH = 11.3G and g-factor 2.001 appear. It is assumed that this spectrum is related to the free radical occurred on the proline residue in collagen molecule. In order to discover .OH hydroxyl radicals even in minor concentration, spin trap 5.5-dimethyl-1-pyrroline N-oxide (DMPO) has been applied. During the irradiation of collagen water solution in the presence of spin trap, EPR spectrum of the DMPO/.OH adduct has not been identified, while the above mentioned spectrum has been observed once the hydrogen peroxide H2O2 and FeSO4 were added to the sample. That means that water photolysis does not take place in collagen water-solution due to UV irradiation. It was suggested that occurrence of hydrogen radical is connected with the electron transmission to the hydrogen ion. The possible source of free electrons can be aromatic residues, photo ionization of which takes place in collagen molecule due to UV irradiation.

Assessment of tissue scaffold degradation using electrochemical techniques

Degradation of a commercially available collagen-glycosaminoglycan dermal equivalent matrix was studied using electrochemical techniques. Degradation was accelerated by exposure to gamma radiation followed by storage at elevated temperatures or exposure to enzymes. The time-dependent diffusion of a small, electrochemically active, molecular probe, potassium ferrocyanide, through the matrix was monitored via changes in the oxidation peak currents of cyclic voltammograms. These measurements were made using a two-compartment diffusion chamber with the sample positioned well away from the working electrodes and a single-compartment electrode cell where the matrix was in direct contact with the working electrode. The relative merits of these two approaches are considered. Regardless of the approach chosen, amperometry appears well suited to monitoring progressive diffusivity changes through mechanically weak porous structures subject to different solution environments.

Kinetics of a collagen-like polypeptide fragmentation after mid-IR free-electron laser ablation

Tissue ablation with mid-infrared irradiation tuned to collagen vibrational modes results in minimal collateral damage. The hypothesis for this effect includes selective scission of protein molecules and excitation of surrounding water molecules, with the scission process currently favored. In this article, we describe the postablation infrared spectral decay kinetics in a model collagen-like peptide (Pro-Pro-Gly)(10). We find that the decay is exponential with different decay times for other, simpler dipeptides. Furthermore, we find that collagen-like polypeptides, such as (Pro-Pro-Gly)(10), show multiple decay times, indicating multiple scission locations and cross-linking to form longer chain molecules. In combination with data from high-resolution mass spectrometry, we interpret these products to result from the generation of reactive intermediates, such as free radicals, cyanate ions, and isocyanic acid, which can form cross-links and protein adducts. Our results lead to a more complete explanation of the reduced collateral damage resulting from infrared laser irradiation through a mechanism involving cross-linking in which collagen-like molecules form a network of cross-linked fibers.

Stabilization of scleral collagen by glycerol aldehyde cross-linking

The paper aims at the evaluation of prospects for using glyceraldehyde as a cross-linking agent for the scleral tissue. Stability parameters (denaturation temperature, Young's modulus, ultimate tensile stress, proteolytic resistance) and analytical parameter (fluorescence intensity) were determined during the glycation process of isolated rabbit sclera. The analysis of fluorescence spectral characteristic provided information about some glycation products. The glyceraldehyde treatment was resulted in a significant increase in thermal stability, proteolytic resistance and improvement of biomechanical characteristics (Young's modulus, ultimate tensile stress). Unique properties of the reaction between scleral collagen and glyceraldehyde are observed at short cross-linking times. The appearance of intermediate collagen fraction with lowest thermal and proteolytic stability was detected.

Nitroxides are more efficient inhibitors of oxidative damage to calf skin collagen than antioxidant vitamins

Reactive oxygen species generated upon UV-A exposure appear to play a major role in dermal connective tissue transformations including degradation of skin collagen. Here we investigate on oxidative damage to collagen achieved by exposure to (i) UV-A irradiation and to (ii) AAPH-derived radicals and on its possible prevention using synthetic and natural antioxidants. Oxidative damage was identified through SDS-PAGE, circular dichroism spectroscopy and quantification of protein carbonyl residues. Collagen (2 mg/ml) exposed to UV-A and to AAPH-derived radicals was degraded in a time- and dose-dependent manner. Upon UV-A exposure, maximum damage was observable at 730 kJ/m2 UV-A, found to be equivalent to roughly 2 h of sunshine, while exposure to 5 mM AAPH for 2 h at 50 degrees C lead to maximum collagen degradation. In both cases, dose-dependent protection was achieved by incubation with muM concentrations of nitroxide radicals, where the extent of protection was shown to be dictated by their structural differences whereas the vitamins E and C proved less efficient inhibitors of collagen damage. These results suggest that nitroxide radicals may be able to prevent oxidative injury to dermal tissues in vivo alternatively to commonly used natural antioxidants.

Non-destructive assessment of parchment deterioration by optical methods

A non-destructive and non-invasive method for quantitative characterization of parchment deterioration, based on spectral measurements, is proposed. Deterioration due to both natural aging (ancient parchments) and artificial aging (achieved by means of controlled UV irradiation and temperature treatment) was investigated. The effect of aging on parchment native fluorescence was correlated with its deterioration condition. Aging causes fluorescence intensity drop, spectral shift of the main peak, and an overall change in the fluorescence spectral features. Digital color imaging analysis based on visible reflectance from the parchment surface was also applied, and the correspondent color components (RGB) were successively correlated with the state of parchment deterioration/aging. The fluorescence and color imaging data were validated by analysis of historical parchments, aged between 50 and 2000 years and covering a large variety of states of deterioration. The samples were independently assessed by traditional microscopy methods. We conclude that the proposed optical method qualifies well as a non-destructive tool for rapid assessment of the stage of parchment deterioration.

Flash photolysis and pulse radiolysis studies on collagen Type I in acetic acid solution

An investigation of the photochemical properties of collagen Type I in acetic acid solution was carried out using nanosecond laser irradiation. The transient spectra of collagen solution excited at 266 nm show two bands. One of them with maximum at 295 nm and the second one with maximum at 400 nm. The peak at 400 nm is assigned to tyrosyl radicals. The first peak of the transient absorption spectra at 295 nm is probably due to photoionisation producing collagen radical cation. The transient for collagen solution in acetic acid at 640 nm was not observed. It is evidence that there is no hydrated electron in the irradiated collagen solution. The reactions of hydrated electrons and (*)OH radicals with collagen have been studied by pulse radiolysis. In the absorption spectra of products resulting from the reaction of collagen with e(aq)(-) no characteristic maximum absorption in UV and visible light region has been observed. In the absorption spectra of products resulting from the reaction of the hydroxyl radicals with collagen two bands have been observed. The first one at 320 nm and the second one at 405 nm. Reaction of (*)OH radicals with tyrosine residues in collagen chains gives rise to Tyr phenoxyl radicals (absorption at 400 nm).

Effects of solar radiation on collagen and chitosan films

Photo-aging and photo-degradation are the deleterious effect of chronic exposure to sun light of many materials made of natural polymers. The resistance of the products on the action of solar radiation is very important for material scientists. The effect of solar radiation on two natural polymers: collagen and chitosan as well as collagen/chitosan blends in the form of thin films has been studied by UV-Vis and FTIR spectroscopy. It was found that UV-Vis spectra, which characterise collagen and collagen/chitosan films, were significantly altered by solar radiation. FTIR spectra of collagen and collagen/chitosan films showed that after solar irradiation the positions of amide A and amide I bands were shifted to lower wavenumbers. There was not any significant alteration of chitosan UV-Vis and FTIR spectra after solar radiation. In the condition of the experiment chitosan films were resistant to the action of solar radiation. The effect of solar UV radiation in comparison to artificial UV radiation has been discussed.

Thermal denaturation of UV-irradiated wet rat tail tendon collagen

The thermal helix-coil transition of UV irradiated collagen in rat tail tendon has been investigated by differential scanning calorimetry. During UVB irradiation the tendons were immersed in water to keep the collagen fibers in a fully hydrated condition at all times. UV irradiation induced changes in collagen which caused both stabilization and destabilization of the triple helix in fibers. The helix-coil transition for non-irradiated collagen occurred near 64 degrees C, for irradiated 1 and 3 h at 66 and 67 degrees C, respectively. After irradiating for longer times (20-66 h) the helix-coil transition peak occurred at much lower temperatures. The peak was very broad and suggested that collagen was reduced by UV to different polypeptides of different molecular weight and different lower thermal stabilities. It was caused by the disruption of a network of hydrogen-bonded water molecules surrounding the collagen macromolecule.

Thermal stability of UV-irradiated collagen in bovine lens capsules and in bovine cornea

The thermal stability of UVB irradiated collagen in bovine lens capsules and in bovine cornea has been investigated by differential scanning calorimetry (DSC). During UVB irradiation the lens capsules and cornea were immersed in water to keep the collagen in a fully hydrated condition at all times. UV irradiation induced changes in collagen which caused both stabilization and destabilization of the collagen structure. The helix-coil transition for non-irradiated collagen in cornea occurred near 66 degrees C, instead for the irradiated one for 3h it occurred at 69 degrees C. After irradiating for longer times (20-96h) the helix-coil transition peak occurred at much lower temperatures. The peak was very broad and suggested that collagen was reduced by UV to different polypeptides of different molecular weight and different lower thermal stabilities. The irradiation of lens capsules with UVB light in vitro resulted in changes in the thermal properties of type-IV collagen consistent with increased cross-linking. DSC of lens capsules showed two major peaks at melting temperatures at 54 degrees C Tm1 and 78 degrees C Tm2, which can be attributed to the denaturation of the triple helix and 7S domains, respectively. UVB irradiation of lens capsules in vitro for 6 h caused an increase in Tm1 from 54 to 57 degrees C. The higher temperature required to denature the type-IV collagen after irradiation in vitro suggested an increase of intermolecular cross-linking.

Free radical scavenging alleviates the biomechanical impairment of gamma radiation sterilized bone tissue

Terminal sterilization of bone allografts by gamma radiation is often essential prior to their clinical use to minimize the risk of infection and disease transmission. While gamma radiation has efficacy superior to other sterilization methods it also impairs the material properties of bone allografts, which may result in premature clinical failure of the allograft. The mechanisms by which gamma radiation sterilization damages bone tissue are not well known although there is evidence that the damage is induced via free radical attack on the collagen. In the light of the existing literature, it was hypothesized that gamma radiation induced biochemical damage to bone's collagen that can be reduced by scavenging for the free radicals generated during the ionizing radiation. It was also hypothesized that this lessening of the extent of biochemical degradation of collagen will be accompanied by alleviation in the extent of biomechanical impairment secondary to gamma radiation sterilization. Standardized tensile test specimens machined from human femoral cortical bone and specimens were assigned to four treatment groups: control, scavenger treated-control, irradiated and scavenger treated-irradiated. Thiourea was selected as the free radical scavenger and it was applied in aqueous form at the concentration of 1.5 M. Monotonic and cyclic mechanical tests were conducted to evaluate the mechanical performance of the treatment groups and the biochemical integrity of collagen molecules were assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native mechanical properties of bone tissue did not change by thiourea treatment only. The effect of thiourea treatment on mechanical properties of irradiated specimens were such that the post-yield energy, the fracture energy and the fatigue life of thiourea treated-irradiated treatment group were 1.9-fold, 3.3-fold and 4.7-fold greater than those of the irradiated treatment group, respectively. However, the mechanical function of thiourea treated and irradiated specimens was not to the level of unirradiated controls. The damage occurred through the cleavage of the collagen backbone as revealed by SDS PAGE analysis. Irradiated specimens did not exhibit a noteworthy amount of intact alpha-chains whereas those irradiated in the presence of thiourea demonstrated intact alpha-chains. Results demonstrated that free radical damage is an important pathway of damage, caused by cleaving the collagen backbone. Blocking the activity of free radicals using the scavenger thiourea reduces the extent of damage to collagen, helping to maintain the mechanical strength of sterilized tissue. Therefore, free radical scavenger thiourea has the potential to improve the functional life-time of the allograft component following transplantation.

Mechanical properties of UV irradiated rat tail tendon (RTT) collagen

The mechanical properties of RTT collagen tendon before and after UV irradiation have been investigated by mechanical testing (Instron). Air-dried tendon were submitted to treatment with UV irradiation (wavelength 254 nm) for different time intervals. The changes in such mechanical properties as breaking strength and percentage elongation have been investigated. The results have shown, that the mechanical properties of the tendon were greatly affected by time of UV irradiation. Ultimate tensile strength and ultimate percentage elongation decreased after UV irradiation of the tendon. Increasing UV irradiation leads to a decrease in Young's modulus of the tendon.

Photoimmobilization of Proteins for Affinity Capture Combined with MALDI TOF MS Analysis

Affinity capture surfaces can be prepared in a number of ways. A method of obtaining such surfaces through UV-activated immobilization of binding proteins using a benzophenone derivative is reported. Photoimmobilized protein G was used to selectively capture and preconcentrate bovine IgG from a mixture with BSA, and the affinity of photoattached concanavalin A toward ovalbumin was compared with that of commercially available concanavalin A on agarose beads. The results of the capture after tryptic digestion were analyzed by MALDI TOF MS. Immobilized trypsin was also prepared through photoimmobilization and later used to digest hemoglobin. Immobilized enzyme digestion resulted in more partial cleavages than solution-phase digestion. More methionine and tryptophan oxidation was also observed. Photoimmobilization was shown to be a quick and easy way of immobilizing ligands on surfaces.