Changes induced by ultraviolet light in fluorescence of collagen in the presence of β-carotene

On the Nature of Stationary and Time-Resolved Fluorescence Spectroscopy of Collagen Powder from Bovine Achilles Tendon

This paper presents a more systematic study of steady-state and time-resolved autofluorescence spectroscopy of collagen isolated from bovine Achilles tendon. In steady-state fluorescence measurements, the excitation and emission spectra of collagen powder, recorded at different fluorescence excitation and detection wavelengths, were compared with the fluorescence excitation and emission spectra of the amino acids phenylalanine, tyrosine, and tryptophan, as well as with similar spectra for 13 autofluorescent collagen cross-links, which have been identified and described in the literature so far. In time-resolved studies, fluorescence was excited by the pulsed light of different wavelengths, and for each excitation wavelength, fluorescence decay was recorded for several detection wavelengths. Data analysis allowed recovery of the fluorescence decay times for each experimental excitation detection event. The obtained information on the decay times of the measured fluorescent signals was discussed, taking into account the available literature data from similar studies of isolated collagen and collagen-rich tissues. Based on the obtained results, it was found that the shape and position of the measured fluorescence excitation and emission spectra of collagen strongly depend on the emission and excitation wavelengths selected in the measurements. From the recorded excitation and emission bands of collagen, it can be concluded with high probability that there are additional, so far unidentified, collagen cross-links, which can be excited at longer excitation wavelengths. In addition, the collagen excitation spectra were measured at longer emission wavelengths at which the collagen cross-links emit fluorescent light. In addition to the emission spectra obtained for excitation in the deep-UV region, the results of time-resolved fluorescence studies with excitation in the deep-UV region and detection at longer wavelengths suggest that fluorescence excitation energy transfer processes occur from the amino acids to the collagen cross-links, and also between the cross-links themselves.

An acetal-based polymeric crosslinker with controlled pH-sensitivity

.An acetal based polymeric cross-linker with controlled pH-sensitivity was used for the synthesis of collagen hydrogels and sponges. The novel cross-linker was synthesized using DE-ATRP and was more biocompatible compared to the commercial 4-star PEG.

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.

Synthesis of fluorescent metal nanoparticles in aqueous solution by photochemical reduction

A facile green chemistry approach for the synthesis of sub-5 nm silver and gold nanoparticles is reported. The synthesis was achieved by a photochemical method using tyrosine as the photoreducing agent. The size of the gold and silver nanoparticles was about 3 and 4 nm, respectively. The nanoparticles were characterized using x-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and photoluminescence spectroscopy. Both silver and gold nanoparticles synthesized by this method exhibited fluorescence properties and their use for cell imaging applications has been demonstrated.

Flash photolysis and pulse radiolysis studies on elastin hydrolysates

The formation of reactive species and free radicals in water soluble elastin hydrolysates have been investigated by pulse radiolysis and flash photolysis. Elastin hydrolysates were obtained by hydrolysis of elastin extracted from aorta. An investigation of the photochemical properties of elastin hydrolysates in water was carried out using nanosecond laser irradiation. The transient spectra of elastin hydrolysates solution excited at 266 nm showed two bands. One of them with maximum at 295 nm and the second one with maximum at 400 nm. The reactions of hydrated electrons and ˙OH radicals with elastin have been studied by pulse radiolysis. In the absorption spectra of products resulting from the reaction of elastin with e(aq)(-) small maximum absorption in UV and visible light was observed. In the absorption spectra of products resulting from the reaction of the hydroxyl radicals with elastin two bands were observed. The first one at 320 nm and the second one at 410 nm. Reaction of OH radicals with elastin hydrolysates lead to formation of Tyr phenoxyl radicals with absorption at 410 nm. The influence of the addition of sodium azide NaN3 on the formation of the transients was evaluated.

Structural study and preliminary biological evaluation on the collagen hydrogel crosslinked by γ-irradiation

Under γ-irradiation, concentrated collagen solutions yielded collagen hydrogels and liquid products. The molecular structure of collagen hydrogels and the source of the liquid products were studied. Furthermore, preliminary biological properties of the hydrogels were investigated. The results revealed that crosslinking occurred to form collagen hydrogel and the crosslinking density increased with the increasing of the absorbed dose, and the collagen hydrogels showed enhanced mechanical properties. Meanwhile, collagen underwent radiation degradation and water was squeezed out from hydrogel by contraction of hydrogel, yielding liquid products. Collagen hydrogels induced by γ-irradiation maintained the backbone structure of collagen, and tyrosine partially involved in crosslinking. The irradiated collagen hydrogels have higher denatured temperature, can promote fibroblasts proliferation, and their degradation rate in vivo depended on the absorbed dose. The comprehensive results suggested that the collagen hydrogels prepared by radiation crosslinking preserved the triple helical conformation, possessed improved thermal stability and mechanical properties, excellent biocompatibility, which is expected to favor its application as biomaterials.

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.

Implications of light energy on food quality and packaging selection

Light energy in the ultraviolet and visible light regions plays a critical role in overall food quality, leading to various degradation and oxidation reactions. Food degradation and oxidation result in the destruction of nutrients and bioactive compounds, the formation of off odors and flavors, the loss of food color, and the formation of toxic substances. Food compounds are sensitive to various light wavelengths. Understanding the effect that specific light wavelengths have on food compounds will allow the development of novel food packaging materials that block the most damaging light wavelengths to photostability of specific food compounds. Future research should focus more specifically on the effect of specific light wavelengths on the quality of specific food products, as there is limited published information on this particular topic. This information also can be directly related to the selection of food packaging materials to retain both high quality and visual clarity of food products exposed to light.

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.

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.

Spectroscopy study on the interaction of quercetin with collagen

In order to understand the interaction between quercetin and collagen clearly, the UV-vis, FTIR-HATR, and fluorescence spectroscopy were used, and the data obtained by these experiments suggested that quercetin could bind to collagen. Results of FTIR-HATR and UV-vis absorption spectra suggested that the interaction of quercetin and collagen did not alter the conformation of collagen. The fluorescence spectra revealed that collagen could cause the quenching of quercetin fluorescence through a dynamic quenching procedure. The calculated quenching constant K(SV) and bimolecular quenching rate constant k(q) suggested that diffusion played a major role in quenching. In addition, the interaction of quercetin and collagen was evaluated by calculating (determining) the number of binding sites (n) and apparent binding constant K(A).

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.

Template-directed patterning of polymers and biomaterials

A novel method of patterning surfaces with synthetic or biological polymers is demonstrated. It consists of using microcontact printing to pattern a gold surface with an adsorbate that imparts hydrophilicity; the remainder of the surface is covered with one that imparts hydrophobicity. 16-Mercaptohexadecanoic acid (MHDA) and 1H,1H,2H,2H-perfluorodecanethiol, respectively, have been used as the hydrophilic and hydrophobic adsorbates. This functionalized gold surface then serves as a template for patterning hydrophilic polymers and biomaterials, which are either spin-coated or drop-cast onto the surface. Using this methodology, it is shown by atomic force microscopy, scanning electron microscopy (SEM), and fluorescence microscopy that micron-scale patterns of a poly(ethylene)-block-poly(ethylene oxide) copolymer, poly-L-tryptophan, and bovine collagen can be fabricated, with these mimicking the MHDA patterns. For the block copolymer, it is found by atomic force microscopy that the heights of the polymer patterns decrease as their widths decrease. This is believed to be due to the inherent instability of tall, narrow polymer structures and the tendency of the polymer to minimize its exposed surface area. For poly-L-tryptophan, two different molecular weights of this polyamino acid have been studied, and different morphologies within the patterned regions are observed. While oligomeric poly-L-tryptophan (1,000-5,000 g/mol) gives smooth MHDA-covered patterns, the higher molecular weight (15,000-50,000 g/mol) yields fibrous ones.

Stabilization of type I collagen against collagenases (type I) and thermal degradation using iron complex

The widespread application of collagen as a biomaterial warrants research in understanding the stabilization of the same. In this study, interaction of iron-tetrakis (hydroxymethyl) phosphonium (THP) complex with type I collagen has been investigated. DSC and hydrothermal measurement studies reveal that the shrinkage temperature of iron-THP treated rat tail tendon (RTT) collagen is 33 degrees C higher than that of native RTT collagen. Fe-THP complex also brings about high degree of enzymatic stability to type I collagen. The effect of Fe-THP on the conformation of collagen was studied using circular dichroism and it was found that no major alterations in the triple helical structure of collagen occur on treatment with Fe-THP. It is observed from viscosity experiment results that though Fe-THP complex is able to bring about long range ordering of collagen, as evident from the thermal and enzymatic stability imparted to collagen, this ordering does not lead to any aggregation of collagen. Since THPS is reducing in nature, it is expected to keep iron in the +2 state and if THP chelates to Fe(II), the hydrolytic behavior of iron can also be controlled.

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.

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.