Probing non-enzymatic glycation of type I collagen: A novel approach using Raman and infrared biophotonic methods

Modulatory role of terminal monomeric flavan-3-ol units in the viscoelasticity of dentin

Flavan-3-ol monomers are the building blocks of proanthocyanidins (PACs), natural compounds from plants shown to mediate specific biologic activities on dentin. While the stereochemistry of the terminal flavan-3-ols, catechin (C) versus epicatechin (EC), impacts the biomechanical properties of the dentin matrix treated with oligomeric PACs, structure-activity relationships driving this bioactivity remain elusive. To gain insights into the modulatory role of the terminal monomers, two highly congruent trimeric PACs from Pinus massoniana only differing in the stereochemistry of the terminal unit (Trimer-C vs. Trimer-EC) were prepared to evaluate their chemical characteristics as well as their effects on the viscoelasticity and biostability of biomodified dentin matrices via infrared spectroscopy and multi-scale dynamic mechanical analyses. The subtle alteration of C versus EC as terminal monomers lead to distinct immediate PAC-trimer biomodulation of the dentin matrix. Nano- and micro-dynamic mechanical analyses revealed that Trimer-EC increased the complex moduli (0.51 GPa) of dentin matrix more strongly than Trimer-C (0.26 GPa) at the nanoscale length (p < 0.001), whereas the reverse was found at the microscale length (p < .001). The damping capacity (tan δ) of dentin matrix decreased by 70% after PAC treatment at the nano-length scale, while increased values were found at the micro-length scale (~0.24) compared to the control (0.18 ; p < .001). An increase in amide band intensities and a decrease of complex moduli was observed after storage in simulated body fluid for both Trimer-C and Trimer-EC modified dentin. The stereochemical configuration of the terminal monomeric units, C and EC, did not impact the chemo-mechanical stability of dentin matrix.

Physicochemical understanding of biomineralization by molecular vibrational spectroscopy: From mechanism to nature

The process and mechanism of biomineralization and relevant physicochemical properties of mineral crystals are remarkably sophisticated multidisciplinary fields that include biology, chemistry, physics, and materials science. The components of the organic matter, structural construction of minerals, and related mechanical interaction, etc., could help to reveal the unique nature of the special mineralization process. Herein, the paper provides an overview of the biomineralization process from the perspective of molecular vibrational spectroscopy, including the physicochemical properties of biomineralized tissues, from physiological to applied mineralization. These physicochemical characteristics closely to the hierarchical mineralization process include biological crystal defects, chemical bonding, atomic doping, structural changes, and content changes in organic matter, along with the interface between biocrystals and organic matter as well as the specific mechanical effects for hardness and toughness. Based on those observations, the special physiological properties of mineralization for enamel and bone, as well as the possible mechanism of pathological mineralization and calcification such as atherosclerosis, tumor micro mineralization, and urolithiasis are also reviewed and discussed. Indeed, the clearly defined physicochemical properties of mineral crystals could pave the way for studies on the mechanisms and applications.

Spectral Features Differentiate Aging-Induced Changes in Parchment-A Combined Approach of UV/VIS, µ-ATR/FTIR and µ-Raman Spectroscopy with Multivariate Data Analysis

From the moment of production, artworks are constantly exposed to changing environmental factors potentially inducing degradation. Therefore, detailed knowledge of natural degradation phenomena is essential for proper damage assessment and preservation. With special focus on written cultural heritage, we present a study on the degradation of sheep parchment employing accelerated aging with light (295-3000 nm) for one month, 30/50/80% relative humidity (RH) and 50 ppm sulfur dioxide with 30/50/80%RH for one week. UV/VIS spectroscopy detected changes in the sample surface appearance, showing browning after light-aging and increased brightness after SO₂-aging. Band deconvolution of ATR/FTIR and Raman spectra and factor analysis of mixed data (FAMD) revealed characteristic changes of the main parchment components. Spectral features for degradation-induced structural changes of collagen and lipids turned out to be different for the employed aging parameters. All aging conditions induced denaturation (of different degrees) indicated by changes in the secondary structure of collagen. Light treatment resulted in the most pronounced changes for collagen fibrils in addition to backbone cleavage and side chain oxidations. Additional increased disorder for lipids was observed. Despite shorter exposure times, SO₂-aging led to a weakening of protein structures induced by transitions of stabilizing disulfide bonds and side chain oxidations.

Effect of ribose incubation on physical, chemical, and mechanical properties of human cortical bone

Raman spectroscopy (RS) is sensitive to the accumulation of advanced glycation end-products (AGEs), and it measures matrix-sensitive properties that correlate with the fracture toughness of human cortical bone. However, it is unclear whether sugar-mediated accumulation of AGEs affects the fracture toughness of human cortical bone in a manner that is consistent with the negative correlations between amide I sub-peak ratios and fracture toughness. Upon machining 64 single-edge notched beam (SENB) specimens from cadaveric femurs (8 male and 7 female donors between 46 years and 61 years of age), pairs of SENB specimens were incubated in 15 mL of phosphate buffered saline with or without 0.1 M ribose for 4 weeks at 37 °C. After acquiring 10 Raman spectra per bone specimen (n = 32 per incubation group), paired SENB specimens were loaded in three-point bending at a quasi-static or a high loading rate approximating 10-4 s-1 or 10-2 s-1, respectively (n = 16 per incubation group per loading rate). While 2 amide I sub-peak ratios, I1670/I1640 and I1670/I1610, decreased by 3-5% with a 100% increase in AGE content, as confirmed by fluorescence measurements, the ribose incubation to accumulate AGEs in bone did not affect linear elastic (KIc) nor non-linear elastic (KJc) measurements of bone's ability to resist crack growth. Moreover, AGE accumulation did not affect the change in these properties when the loading rate changed. Increasing the loading rate increased KIc but decreased KJc. Ribose incubation did not affect mineral-related RS properties such as mineral-to-matrix ratios, Type B carbonate substitutions, and crystallinity. It did however increase the thermal stability of demineralized bone (differential scanning calorimetry), without affecting the network connectivity of the organic matrix (i.e., maximum slope during a hydrothermal isometric tension test of demineralized bone). In conclusion, RS is sensitive to AGE accumulation via the amide I band (plus the hydroxyproline-to-proline ratio), but the increase in AGE content due to ribose incubation was not sufficient to affect the fracture toughness of human cortical bone.

AGE-breaker ALT711 reverses glycation-mediated cancer cell migration

Diabetes is associated with increased risk of breast cancer and worse prognoses for cancer patients. Hyperglycemia can result in increased glycation, the process wherein crosslinkages are formed between sugars and extracellular matrix (ECM) proteins through the formation of advanced glycation endproducts (AGEs). Although accumulation of AGEs occurs naturally in vivo over time, it is greatly accelerated by the hyperglycemic environment of diabetic patients. AGE accumulation has been linked to stiffening-related diseases such as hypertension, cancer metastasis, and neurodegenerative disorders. In response, several AGE-inhibiting and AGE-breaking drugs have received significant attention for their ability to reduce AGE accumulation. The resulting effects of these drugs on cell behavior is not well understood. In this study, we measured cancer cell migration in glycated collagen with and without the AGE-breaking drug alagebrium chloride (ALT711) to investigate the drug's ability to disrupt ECM crosslinks and reduce tumor cell spreading, contractility, and migration. The mechanical properties and chemical composition of collagen glycated with increasing concentrations of glucose with and without ALT711 treatment were measured. Increasing glucose concentration resulted in increased AGE accumulation and matrix stiffness as well as increased cancer cell contractility, elongation, and migration. Treatment with ALT711 significantly lowered AGE accumulation within the collagen, decreased collagen stiffness, and reduced cell migration. These findings suggest that while hyperglycemia can increase collagen matrix stiffness, resulting in increased breast cancer cell migration, an AGE-breaker can reverse this phenotype and may be a viable treatment option for reducing cancer cell migration due to glycation.

Birefringence effect studies of collagen formed by nonenzymatic glycation using dual-retarder Mueller polarimetry

SIGNIFICANCE

Nonenzymatic glycation of collagen covalently attaches an addition of sugar molecules that initially were involved in a reversibly reaction with amino groups on the protein. Due to the ultimate formation of stable irreversible advanced glycation end products, the process of glycation leads to abnormal irreversible cross-linking, which ultimately accumulates with age and/or diabetes in the extracellular matrix, altering its organization.

AIM

We report the use of dual-retarder Mueller polarimetry in conjunction with phase retardance to differentiate collagen cross-linking in a normal collagen gel matrix from that in tissues with nonenzymatic cross-linking.

APPROACH

A dual-liquid crystal-based Mueller polarimetry system that involves electronic modulation of polarization state generators (PSGs) was employed to produce all types of polarization states without moving any part and enable detection of the signal directly using a Stokes polarimeter. The linear phase retardance response was obtained for the characterization of the solution and gel forms of collagen using differential Mueller matrix analysis.

RESULTS

We found that linear phase retardance measurements via differential Mueller matrix polarimetry successfully differentiated collagen gel matrices with different degrees of cross-linking formed by a nonenzymatic glycation process and demonstrated that this technology constitutes a quick and simple modality.

CONCLUSIONS

This approach has high sensitivity for studying differences in fibrillar cross-linking in glycated collagen. Further, our work suggests that this method of structural analysis has potential clinical diagnostic value owing to its noninvasive and cost-efficient nature.

Various Simulated Body Fluids Lead to Significant Differences in Collagen Tissue Engineering Scaffolds

This study aims to point out the main drawback with respect to the design of simulated body environments. Three media commonly used for the simulation of the identical body environment were selected, i.e., Kokubo’s simulated body fluid that simulates the inorganic component of human blood plasma, human blood plasma, and phosphate buffer saline. A comparison was performed of the effects of the media on collagen scaffolds. The mechanical and structural effects of the media were determined via the application of compression mechanical tests, the determination of mass loss, and image and micro-CT analyses. The adsorption of various components from the media was characterized employing energy-dispersive spectrometry. The phase composition of the materials before and after exposure was determined using X-ray diffraction. Infrared spectroscopy was employed for the interpretation of changes in the collagen secondary structure. Major differences in terms of the mechanical properties and mass loss were observed between the three media. Conversely, only minor structural changes were detected. Since no general recommendation exists for selecting the simulated body environment, it is necessary to avoid the simplification of the results and, ideally, to utilize alternative methods to describe the various aspects of degradation processes that occur in the media.

A dynamic mechanical method to assess bulk viscoelastic behavior of the dentin extracellular matrix

OBJECTIVES

To develop a protocol for assessment of the bulk viscoelastic behavior of dentin extracellular matrix (ECM), and to assess relationships between induced collagen cross-linking and viscoelasticity of the dentin ECM.

METHODS

Dentin ECM was treated with agents to induce exogenous collagen cross-linking: proanthocyanidins (PACs) from Vitis vinifera - VVe, PACs from Pinus massoniana - PMe, glutaraldehyde - (GA), or kept untreated (control). A dynamic mechanical strain sweep method was carried out in a 3-point bending submersion clamp at treatment; after protein destabilization with 4 M urea and after 7-day, 6-month, and 12-month incubation in simulated body fluid. Tan δ, storage (E'), loss (E"), and complex moduli (E*) were calculated and data were statistically analyzed using two-way ANOVA and post-hoc tests (α = 0.05). Chemical analysis of dentin ECM before and after protein destabilization was assessed with ATR-FTIR spectroscopy.

RESULTS

Significant interactions between study factors (treatment vs. time points, p < 0.001) were found for all viscoelastic parameters. Despite a significant decrease in all moduli after destabilization, PAC-treated dentin remained statistically higher than control (p < 0.001), indicating permanent mechanical enhancement after biomodification. Covalently crosslinked, GA-treated dentin was unaffected by destabilization (p = 0.873) and showed the lowest damping capacity (tan δ) at all time points (p < 0.001). After 12 months, the damping capacity of PMe and VVe groups decreased significantly. Changes in all amide IR resonances revealed a partial chemical reversal of PAC-mediated biomodification.

SIGNIFICANCE

Viscoelastic measurements and IR spectroscopy aid in elucidating the role of inter-molecular collagen cross-linking in the mechanical behavior of dentin ECM.

Analysis of Hepatic Fibrosis Characteristics in Cirrhotic Patients with and without Hepatocellular Carcinoma by FTIR Spectral Imaging

The evolution of cirrhosis is marked by quantitative and qualitative modifications of the fibrosis tissue and an increasing risk of complications such as hepatocellular carcinoma (HCC). Our purpose was to identify by FTIR imaging the spectral characteristics of hepatic fibrosis in cirrhotic patients with and without HCC. FTIR images were collected at projected pixel sizes of 25 and 2.7 μm from paraffinized hepatic tissues of five patients with uncomplicated cirrhosis and five cirrhotic patients with HCC and analyzed by k-means clustering. When compared to the adjacent histological section, the spectral clusters corresponding to hepatic fibrosis and regeneration nodules were easily identified. The fibrosis area estimated by FTIR imaging was correlated to that evaluated by digital image analysis of histological sections and was higher in patients with HCC compared to those without complications. Qualitative differences were also observed when fibrosis areas were specifically targeted at higher resolution. The partition in two clusters of the fibrosis tissue highlighted subtle differences in the spectral characteristics of the two groups of patients. These data show that the quantitative and qualitative changes of fibrosis tissue occurring during the course of cirrhosis are detectable by FTIR imaging, suggesting the possibility of subclassifying cirrhosis into different steps of severity.

Obtaining glycoconjugates of marine origin via Maillard reaction and their cytotoxic effect: an alternative for the use of animal byproducts

BACKGROUND

Protein glycation by Maillard reaction is commonly used to improve the functional and bioactive properties of food proteins. It is also known that this glycation method can be accelerated by heat without the need for chemical reagents that could be harmful to health. In this study, glycoconjugates were obtained from a mixture of connective tissue proteins (CTP) from jumbo squid (Dosidicus gigas) and two different sugars, dextran (DEX; 10 kDa) and glucose (GLU), using protein-to-carbohydrate ratios of 1:2 and 1:3, in solution at 50 °C for 6 h. The glycation products were characterized by means of their physicochemical properties and cytotoxic effect.

RESULTS

The intensity of the browning measured at A_420nm and A_294nm in glycoconjugates showed no significant difference (P < 0.05). CTP-DEX (1:2) and CTP-DEX (1:3) were those products with the greatest fluorescence related to the intermediate stage in the Maillard reaction, and also with the highest degree of glycation, which was confirmed using o-phthaldialdehyde assay and Fourier transform infrared analysis. The values of cellular viability for CTP-GLU (1:3), CTP-DEX (1:2, 1:3) as well as CTP (0, 6 h) were around 92-103%.

CONCLUSIONS

The operational parameters used in the glycation process achieved the formation of glycoconjugates from proteins of D. gigas, showing no cytotoxic effect on the HaCaT cell line. This research proposes an alternative for the modification of proteins and opens the way to future investigations regarding the bioactivity of these macromolecules to have applications for the use of byproducts in food science and technology. © 2020 Society of Chemical Industry.

Detection of Age-Related Changes in Tendon Molecular Composition by Raman Spectroscopy-Potential for Rapid, Non-Invasive Assessment of Susceptibility to Injury

The lack of clinical detection tools at the molecular level hinders our progression in preventing age-related tendon pathologies. Raman spectroscopy can rapidly and non-invasively detect tissue molecular compositions and has great potential for in vivo applications. In biological tissues, a highly fluorescent background masks the Raman spectral features and is usually removed during data processing, but including this background could help age differentiation since fluorescence level in tendons increases with age. Therefore, we conducted a stepwise analysis of fluorescence and Raman combined spectra for better understanding of the chemical differences between young and old tendons. Spectra were collected from random locations of vacuum-dried young and old equine tendon samples (superficial digital flexor tendon (SDFT) and deep digital flexor tendon (DDFT), total n = 15) under identical instrumental settings. The fluorescence-Raman spectra showed an increase in old tendons as expected. Normalising the fluorescence-Raman spectra further indicated a potential change in intra-tendinous fluorophores as tendon ages. After fluorescence removal, the pure Raman spectra demonstrated between-group differences in CH2 bending (1450 cm-1) and various ring-structure and carbohydrate-associated bands (1000-1100 cm-1), possibly relating to a decline in cellular numbers and an accumulation of advanced glycation end products in old tendons. These results demonstrated that Raman spectroscopy can successfully detect age-related tendon molecular differences.

Mechanisms of soft tissue and protein preservation in Tyrannosaurus rex

The idea that original soft tissue structures and the native structural proteins comprising them can persist across geological time is controversial, in part because rigorous and testable mechanisms that can occur under natural conditions, resulting in such preservation, have not been well defined. Here, we evaluate two non-enzymatic structural protein crosslinking mechanisms, Fenton chemistry and glycation, for their possible contribution to the preservation of blood vessel structures recovered from the cortical bone of a Tyrannosaurus rex (USNM 555000 [formerly, MOR 555]). We demonstrate the endogeneity of the fossil vessel tissues, as well as the presence of type I collagen in the outermost vessel layers, using imaging, diffraction, spectroscopy, and immunohistochemistry. Then, we use data derived from synchrotron FTIR studies of the T. rex vessels to analyse their crosslink character, with comparison against two non-enzymatic Fenton chemistry- and glycation-treated extant chicken samples. We also provide supporting X-ray microprobe analyses of the chemical state of these fossil tissues to support our conclusion that non-enzymatic crosslinking pathways likely contributed to stabilizing, and thus preserving, these T. rex vessels. Finally, we propose that these stabilizing crosslinks could play a crucial role in the preservation of other microvascular tissues in skeletal elements from the Mesozoic.

Interaction of the synthetic antithrombotic peptide P10 with thrombin: a spectroscopy study

Thrombin is a critical serine protease in the coagulation system and is widely used as a target protein for antithrombotics. Spectroscopic analysis is a simple and effective method that is used to study the interaction between small molecules and proteins. In this study, the interactions of a potential antithrombotic peptide AGFAGDDAPR (P10) with thrombin were investigated by fluorescence spectroscopy, UV-vis spectroscopy, circular dichroism, Fourier-transform infrared spectroscopy and Raman spectroscopy, respectively. The results showed that the peptide P10 bonded to thrombin via hydrogen bonding and van der Waals forces, resulting in fluorescence quenching. And, the secondary structure of thrombin changed, the β-sheet decreased, and the random coil increased. The peptide P10 bonded to proline and lysine, and changed the space structure of thrombin, resulting in inhibition of thrombin activity. The results contributed to exploration of the mechanism of this potential antithrombotic drug interaction with thrombin in order to provide a preliminary understanding of the pharmacodynamic properties of P10.

Assessing glycation-mediated changes in human cortical bone with Raman spectroscopy

Establishing a non-destructive method for spatially assessing advanced glycation end-products (AGEs) is a potentially useful step toward investigating the mechanistic role of AGEs in bone quality. To test the hypothesis that the shape of the amide I in the Raman spectroscopy (RS) analysis of bone matrix changes upon AGE accumulation, we incubated paired cadaveric cortical bone in ribose or glucose solutions and in control solutions for 4 and 16 weeks, respectively, at 37°C. Acquiring 10 spectra per bone with a 20X objective and a 830 nm laser, RS was sensitive to AGE accumulation (confirmed by biochemical measurements of pentosidine and fluorescent AGEs). Hyp/Pro ratio increased upon glycation using either 0.1 M ribose, 0.5 M ribose or 0.5 M glucose. Glycation also decreased the amide I sub-peak ratios (cm-1 ) 1668/1638 and 1668/1610 when directly calculated using either second derivative spectrum or local maxima of difference spectrum, though the processing method (eg, averaged spectrum vs individual spectra) to minimize noise influenced detection of differences for the ribose-incubated bones. Glycation however did not affect these sub-peak ratios including the matrix maturity ratio (1668/1690) when calculated using indirect sub-band fitting. The amide I sub-peak ratios likely reflected changes in the collagen I structure.

Assessment of collagen quality associated with non-enzymatic cross-links in human bone using Fourier-transform infrared imaging

Aging and many disease conditions, most notably diabetes, are associated with the accumulation of non-enzymatic cross-links in the bone matrix. The non-enzymatic cross-links, also known as advanced glycation end products (AGEs), occur at the collagen tissue level, where they are associated with reduced plasticity and increased fracture risk. In this study, Fourier-transform infrared (FTIR) imaging was used to detect spectroscopic changes associated with the formation of non-enzymatic cross-links in human bone collagen. Here, the non-enzymatic cross-link profile was investigated in one cohort with an in vitro ribose treatment as well as another cohort with an in vivo bisphosphonate treatment. With FTIR imaging, the two-dimensional (2D) spatial distribution of collagen quality associated with non-enzymatic cross-links was measured through the area ratio of the 1678/1692cm^-1 subbands within the amide I peak, termed the non-enzymatic crosslink-ratio (NE-xLR). The NE-xLR increased by 35% in the ribation treatment group in comparison to controls (p<0.005), with interstitial bone tissue being more susceptible to the formation of non-enzymatic cross-links. Ultra high-performance liquid chromatography, fluorescence microscopy, and fluorometric assay confirm a correlation between the non-enzymatic cross-link content and the NE-xLR ratio in the control and ribated groups. High resolution FTIR imaging of the 2D bone microstructure revealed enhanced accumulation of non-enzymatic cross-links in bone regions with higher tissue age (i.e., interstitial bone). This non-enzymatic cross-link ratio (NE-xLR) enables researchers to study not only the overall content of AGEs in the bone but also its spatial distribution, which varies with skeletal aging and diabetes mellitus and provides an additional measure of bone's propensity to fracture.

Infrared microspectroscopic determination of collagen cross-links in articular cartilage

Collagen forms an organized network in articular cartilage to give tensile stiffness to the tissue. Due to its long half-life, collagen is susceptible to cross-links caused by advanced glycation end-products. The current standard method for determination of cross-link concentrations in tissues is the destructive high-performance liquid chromatography (HPLC). The aim of this study was to analyze the cross-link concentrations nondestructively from standard unstained histological articular cartilage sections by using Fourier transform infrared (FTIR) microspectroscopy. Half of the bovine articular cartilage samples ( n = 27 ) were treated with threose to increase the collagen cross-linking while the other half ( n = 27 ) served as a control group. Partial least squares (PLS) regression with variable selection algorithms was used to predict the cross-link concentrations from the measured average FTIR spectra of the samples, and HPLC was used as the reference method for cross-link concentrations. The correlation coefficients between the PLS regression models and the biochemical reference values were r = 0.84 ( p < 0.001 ), r = 0.87 ( p < 0.001 ) and r = 0.92 ( p < 0.001 ) for hydroxylysyl pyridinoline (HP), lysyl pyridinoline (LP), and pentosidine (Pent) cross-links, respectively. The study demonstrated that FTIR microspectroscopy is a feasible method for investigating cross-link concentrations in articular cartilage.

Highlighting the impact of aging on type I collagen: label-free investigation using confocal reflectance microscopy and diffuse reflectance spectroscopy in 3D matrix model

During aging, alterations of extracellular matrix proteins contribute to various pathological phenotypes. Among these alterations, type I collagen cross-linking and associated glycation products accumulation over time detrimentally affects its physico-chemical properties, leading to alterations of tissue biomechanical stability. Here, different-age collagen 3D matrices using non-destructive and label-free biophotonic techniques were analysed to highlight the impact of collagen I aging on 3D constructs, at macroscopic and microscopic levels. Matrices were prepared with collagens extracted from tail tendons of rats (newborns, young and old adults) to be within the physiological aging process. The data of diffuse reflectance spectroscopy reveal that aging leads to an inhibition of fibril assembly and a resulting decrease of gel density. Investigations by confocal reflectance microscopy highlight poor-fibrillar structures in oldest collagen networks most likely related to the glycation products accumulation. Complementarily, an infrared analysis brings out marked spectral variations in the Amide I profile, specific of the peptidic bond conformation and for carbohydrates vibrations as function of collagen-age. Interestingly, we also highlight an unexpected behavior for newborn collagen, exhibiting poorly-organized networks and microscopic features close to the oldest collagen. These results demonstrate that changes in collagen optical properties are relevant for investigating the incidence of aging in 3D matrix models.

DFT:B3LYP/3-21G theoretical insights on the confocal Raman experimental observations in skin dermis of healthy young, healthy elderly, and diabetic elderly women

In the confocal Raman spectra of skin dermis, the band area in the spectral region of proline and hydroxyproline varies according to the age and health condition of the volunteers, classified as healthy young women, healthy elderly women, and diabetic elderly women. Another observation refers to the intensity variation and negative Raman shift of the amide I band. To understand these effects, we adopted a model system using the DFT/B3LYP:3-21G procedure, considering the amino acid chain formed by glycine, hydroxyproline, proline, and alanine, which interacts with two and six water molecules. Through these systems, polarizability variations were analyzed to correlate its values with the observed Raman intensities of the three groups of volunteers and to assign the vibrational spectra of the skin dermis. As a way to correlate other experimental trends, we propose a model of chemical reaction of water interchange between the bonding amino acids, in which water molecules are attached with glucose by hydrogen bonds. The theoretical results are in accordance with the observed experimental trends.

The collaggrecan: Synthesis and visualization of an artificial proteoglycan

An artificial aggrecan-like proteoglycan has been designed and synthesized in vitro. At variance with natural proteoglycans, whose glycosaminoglycan chains are always O-linked via a tetrasaccharide bridge to the serine residues of a specific protein core, the present structure consists of chondroitin-6-sulfate chains directly bound to the lysine and hydroxylysine residues of a collagen molecule backbone. The resulting macromolecule has been characterized by histochemistry, atomic force microscopy and FTIR. The number of variables involved (e.g., length and type of the collagen backbone, glycosaminoglycan species, sulfation type and pattern, molecular weight, number and length of side chains, etc.) makes possible to conceive an almost endless variety of artificial proteoglycans, each precisely tailored to a specific functional role. In addition to their use as biomaterials, glycated collagens interact with cells in complex ways and a previous study has already shown the ability of a glycated collagen to redirect fibroblastoma cells from proliferation to differentiation. The research is still underway.

Stable Incretin Mimetics Counter Rapid Deterioration of Bone Quality in Type 1 Diabetes Mellitus

Type 1 diabetes mellitus is associated with a high risk for bone fractures. Although bone mass is reduced, bone quality is also dramatically altered in this disorder. However, recent evidences suggest a beneficial effect of the glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) pathways on bone quality. The aims of the present study were to conduct a comprehensive investigation of bone strength at the organ and tissue level; and to ascertain whether enzyme resistant GIP or GLP-1 mimetic could be beneficial in preventing bone fragility in type 1 diabetes mellitus. Streptozotocin-treated mice were used as a model of type 1 diabetes mellitus. Control and streptozotocin-diabetic animals were treated for 21 days with an enzymatic-resistant GIP peptide ([D-Ala(2) ]GIP) or with liraglutide (each at 25 nmol/kg bw, ip). Bone quality was assessed at the organ and tissue level by microCT, qXRI, 3-point bending, qBEI, nanoindentation, and Fourier-transform infrared microspectroscopy. [D-Ala2]GIP and liraglutide treatment did prevent loss of whole bone strength and cortical microstructure in the STZ-injected mice. However, tissue material properties were significantly improved in STZ-injected animals following treatment with [D-Ala2]GIP or liraglutide. Treatment of STZ-diabetic mice with [D-Ala(2) ]GIP or liraglutide was capable of significantly preventing deterioration of the quality of the bone matrix. Further studies are required to further elucidate the molecular mechanisms involved and to validate whether these findings can be translated to human patients.

RM1 semi empirical and DFT: B3LYP/3-21G theoretical insights on the confocal Raman experimental observations in qualitative water content of the skin dermis of healthy young, healthy elderly and diabetic elderly women's

In the confocal Raman spectra of skin dermis, the band area of proline and hydroxyproline in the fingerprint spectral region of 800-1000 cm(-1), where their vibrational modes are assigned, varied according to the age of the woman volunteers. The other aging effect observed in the Raman spectra is in the Amide I band in the spectral region between 1580 and 1720 cm(-1), where a softening in the Raman shift and intensity variation is detected depending of the vibrational groups. It is well known that the water quantity in healthy human skin dermis increases with age. However, in the elderly with diabetic disease, the increased sugar content directly affect the proline and hydroxyproline peaks as well as the water content in the dermis. The first approach in this work was theoretically modeling these systems using the RM1 semi empirical method, which represent proline and hydroxyproline interacting with one to four water molecule and with glucose. This task predicted how many hydrogen bonds were formed with the two amino acids and glucose. The subsequent model was built using DFT/B3LYP:3-21G procedures considering the amino acids chain formed by hydroxyproline and proline alone, which interact with one and four water molecules. We analyzed the dipole moment and polarizability variation to determine the hydrogen bonds in these systems. We chose the DFT/B3LYP:3-21G method to assign the vibrational modes of the skin dermis as a way to correlate the experimental trends. To explain the profile of lower intensity in the hydroxyproline and proline spectral region in diabetic elderly women, we proposed a chemical reaction of water interchange between the bonding amino acids and glucose, and we considered also the natural decreasing of collagen due to the glycation process. Theoretical results agree well with the observed experimental results.

In vitro glycation of articular cartilage alters the biomechanical response of chondrocytes in a depth-dependent manner

OBJECTIVE

To determine if increasing cartilage cross-links through in vitro glycation of cartilage explants can alter the biomechanical response of chondrocytes to compressive deformation.

METHOD

Bovine osteochondral explants were either incubated with cell culture solution supplemented with (n = 7) or without (n = 7) ribose for 42 h in order to induce glycation. Deformation-induced changes in cell volume, dimensions and local tissue strains were determined through confocal laser scanning microscopy (CLSM) and the use of a custom built micro-compression device. Osteochondral explants were also utilized to demonstrate changes in depth-wise tissue properties, biomechanical tissue properties and cross-links such as pentosidine (Pent), hydroxylysyl pyridinoline (HP) and lysyl pyridinoline (LP).

RESULTS

The ribose treated osteochondral samples experienced reduced cell volume deformation in the upper tissue zone by ∼ 8% (P = 0.005), as compared the control samples, through restricting cell expansion. In the deeper tissue zone, cell volume deformation was increased by ∼ 12% (P < 0.001) via the transmission of mechanical signals further into the tissue depth. Biomechanical testing of the ribose treated osteochondral samples demonstrated an increase in the equilibrium and dynamic strain dependent moduli (P < 0.001 and P = 0.008, respectively). The biochemical analysis revealed an increase in Pent cross-links (P < 0.001). Depth-wise tissue property analyses revealed increased levels of carbohydrate content, greater levels of fixed charge density and an increased carbohydrate to protein ratio from 6 to 16%, 55-100% and 72-79% of the normalized tissue thickness (from the surface), respectively, in the ribose-treated group (P < 0.05).

CONCLUSION

In vitro glycation alters the biomechanical response of chondrocytes in cartilage differently in upper and deeper zones, offering possible insights into how aging could alter cell deformation behavior in cartilage.

Neoglucosylated collagen matrices drive neuronal cells to differentiate

Despite the relevance of carbohydrates as cues in eliciting specific biological responses, glycans have been rarely exploited in the study of neuronal physiology. We report thereby the study of the effect of neoglucosylated collagen matrices on neuroblastoma F11 cell line behavior. Morphological and functional analysis clearly showed that neoglucosylated collagen matrices were able to drive cells to differentiate. These data show for the first time that F11 cells can be driven from proliferation to differentiation without the use of chemical differentiating agents. Our work may offer to cell biologists new opportunities to study neuronal cell differentiation mechanisms in a cell environment closer to physiological conditions.

Thiol-ene mediated neoglycosylation of collagen patches: a preliminary study

Despite the relevance of carbohydrates as cues in eliciting specific biological responses, the covalent surface modification of collagen-based matrices with small carbohydrate epitopes has been scarcely investigated. We report thereby the development of an efficient procedure for the chemoselective neoglycosylation of collagen matrices (patches) via a thiol-ene approach, between alkene-derived monosaccharides and the thiol-functionalized material surface. Synchrotron radiation-induced X-ray photoelectron spectroscopy (SR-XPS), Fourier transform-infrared (FT-IR), and enzyme-linked lectin assay (ELLA) confirmed the effectiveness of the collagen neoglycosylation. Preliminary biological evaluation in osteoarthritic models is reported. The proposed methodology can be extended to any thiolated surface for the development of smart biomaterials for innovative approaches in regenerative medicine.