An investigation of composition, morphology, mechanical properties, and microdamage accumulation of human type 2 diabetic bone.

This study investigates the biomechanics of type 2 diabetic bone fragility through a multiscale experimental strategy that considers structural, mechanical, and compositional components of ex vivo human trabecular and cortical bone. Human tissue samples were obtained from the femoral heads of patients undergoing total hip replacement. Mechanical testing was carried out on isolated trabecular cores using monotonic and cyclic compression loading and nanoindentation experiments, with bone microdamage analysed using micro-computed tomography (CT) imaging. Bone composition was evaluated using Raman spectroscopy, high-performance liquid chromatography, and fluorometric spectroscopy. It was found that human type 2 diabetic bone had altered mechanical, compositional, and morphological properties compared to non-type 2 diabetic bone. High-resolution micro-CT imaging showed that cores taken from the central trabecular region of the femoral head had higher bone mineral density (BMD), bone volume, trabecular thickness, and reduced trabecular separation. Type 2 diabetic bone also had enhanced macro-mechanical compressive properties under mechanical loading compared to non-diabetic controls, with significantly higher apparent modulus, yield stress, and pre-yield toughness evident, even when properties were normalised against the bone volume. Using nanoindentation, there were no significant differences in the tissue-level mechanical properties of cortical or trabecular bone in type 2 diabetic samples compared to controls. Through compositional analysis, higher levels of furosine were found in type 2 diabetic trabecular bone, and an increase in both furosine and carboxymethyl-lysine (an advanced glycation end-product) was found in cortical bone. Raman spectroscopy showed that type 2 diabetic bone had a higher mineral-to-matrix ratio, carbonate substitution, and reduced crystallinity compared to the controls. Together, this study shows that type 2 diabetes leads to distinct changes in both organic and mineral phases of the bone tissue matrix, but these changes did not coincide with any reduction in the micro- or macro-mechanical properties of the tissue under monotonic or cyclic loading.

Accumulation of Carbamylation-Derived Products in Aneurysmal Aorta.

INTRODUCTION: Carbamylation is a nonenzymatic post-translational modification of proteins characterized by the binding of isocyanic acid to amino groups of proteins, which leads to the alteration of their properties. An increase in serum carbamylation-derived products, including homocitrulline (HCit), has been shown to be associated with the development of cardiovascular diseases. METHODS: HCit was quantified by LC-MS/MS within extracts of aneurysmal and control human aortas. A mouse model of aortic aneurysm (ApoE-/- mice perfused with angiotensin II and fed with sodium cyanate) was used to evaluate the role of carbamylation in aneurysm development. RESULTS: HCit quantification showed a greater heterogeneity of values in aneurysmal aortas in comparison with control ones. At the maximum diameter of dilation, HCit values were significantly higher (+94%, p < 0.05) compared with less dilated areas. No differences were observed according to aneurysm size or when comparing ruptured and unruptured aneurysms. No significant effect of carbamylation on aneurysm development was observed using the animal model. CONCLUSIONS: These results evidenced the accumulation of HCit within aneurysmal aortas but do not allow concluding about the exact participation of protein carbamylation in the development of human abdominal aortic aneurysms.

Biochemical and morpho-mechanical properties, and structural organization of rat tail tendon collagen in diet-induced obesity model.

We have investigated the impact of obesity on the structural organization, morpho-mechanical properties of collagen fibers from rat tail tendon fascicles (RTTFs). Polarized Raman microspectroscopy showed that the collagen bands 855, 875, 938, and 960 cm-1 as well as those 1631 and 1660 cm-1 were affected by diet. Mechanical properties exhibited an increase in the yield strength from control (CTRL) to high fat (HF) diet (9.60 ± 1.71 and 13.09 ± 1.81 MPa) (p < 0.01) and ultimate tensile strength (13.12 ± 2.37 and 18.32 ± 2.83 MPa) (p < 0.05) with no significant change in the Young's Modulus. During mechanical, the band at 875 cm-1 exhibited the most relevant frequency shift (2 cm-1). The intensity of those at 855, 875, and 938 cm-1 in HF collagen displayed a comparable response to mechanical stress as compared to CTRL collagen with no significant diet-related changes in the Full Width at Half Maximum. Second harmonic generation technique revealed i) similar fiber straightness (0.963 ± 0.004 and 0.965 ± 0.003) and ii) significant changes in fibers diameter (1.48 ± 0.07 and 1.52 ± 0.08 µm) (p < 0.05) and length (22.06 ± 2.38 and 29.00 ± 3.76 µm) (p < 0.001) between CTRL and HF diet, respectively. The quantification of advanced glycation end products (AGEs) revealed an increase in both carboxymethyl-lysine and total fluorescence AGEs from CTRL to HF RTTFs.

An integrated approach to investigate age-related modifications of morphological, mechanical and structural properties of type I collagen.

The main propose of this study is to characterize the impact of chronological aging on mechanical, structural, biochemical, and morphological properties of type I collagen. We have developed an original approach combining a stress-strain measurement device with a portable Raman spectrometer to enable simultaneous measurement of Raman spectra during stress vs strain responses of young adult, adult and old rat tail tendon fascicles (RTTFs). Our data showed an increase in all mechanical properties such as Young's modulus, yield strength, and ultimate tensile strength with aging. At the molecular level, Raman data revealed that the most relevant frequency shift was observed at 938 cm-1 in Old RTTFs, which is assigned to the C-C. This suggested a long axis deformation of the peptide chains in Old RTTFs during tensile stress. In addition, the intensity of the band at 872 cm-1, corresponding to hydroxyproline decreased for young adult RTTFs and increased for the adult ones, while it remained unchanged for Old RTTFs during tensile stress. The amide III band (1242 and 1265 cm-1) as well as the band ratios I1631/ I1663 and I1645 / I1663 responses to tensile stress were depending on mechanical phases (toe, elastic and plastic). The quantification of advanced glycation end-products by LC-MS/MS and spectrofluorometry showed an increase in their content with aging. This suggested that the accumulation of such products was correlated to the alterations observed in the mechanical and molecular properties of RTTFs. Analysis of the morphological properties of RTTFs by SHG combined with CT-FIRE software revealed an increase in length and straightness of collagen fibers, whereas their width and wavy fraction decreased. Our integrated study model could be useful to provide additional translational information to monitor progression of diseases related to collagen remodeling in musculoskeletal disorders. STATEMENT OF SIGNIFICANCE: Type I collagen is the major component of the extracellular matrix. Its architectural and structural organization plays an important role in the mechanical properties of many tissues at the physiological and pathological levels. The objective of this work is to develop an integrated approach to bring a new insight on the impact of chronological aging on the structural organization and mechanical properties of type I collagen. We combined a portable Raman spectrometer with a mechanical tensile testing device in order to monitor in real time the changes in the Raman fingerprint of type I collagen fibers during the mechanical stress. Raman spectroscopy allowed the identification of the type I collagen bonds that were affected by mechanical stress in a differential manner with aging.

Carbamylation of elastic fibers is a molecular substratum of aortic stiffness.

Because of their long lifespan, matrix proteins of the vascular wall, such as elastin, are subjected to molecular aging characterized by non-enzymatic post-translational modifications, like carbamylation which results from the binding of cyanate (mainly derived from the dissociation of urea) to protein amino groups. While several studies have demonstrated a relationship between increased plasma concentrations of carbamylated proteins and the development of cardiovascular diseases, molecular mechanisms explaining the involvement of protein carbamylation in these pathological contexts remain to be fully elucidated. The aim of this work was to determine whether vascular elastic fibers could be carbamylated, and if so, what impact this phenomenon would have on the mechanical properties of the vascular wall. Our experiments showed that vascular elastin was carbamylated in vivo. Fiber morphology was unchanged after in vitro carbamylation, as well as its sensitivity to elastase degradation. In mice fed with cyanate-supplemented water in order to increase protein carbamylation within the aortic wall, an increased stiffness in elastic fibers was evidenced by atomic force microscopy, whereas no fragmentation of elastic fiber was observed. In addition, this increased stiffness was also associated with an increase in aortic pulse wave velocity in ApoE-/- mice. These results provide evidence for the carbamylation of elastic fibers which results in an increase in their stiffness at the molecular level. These alterations of vessel wall mechanical properties may contribute to aortic stiffness, suggesting a new role for carbamylation in cardiovascular diseases.

Proteasome-dependent degradation of intracellular carbamylated proteins.

Carbamylation, which corresponds to the binding of isocyanic acid to the amino groups of proteins, is a nonenzymatic post-translational modification responsible for alterations of protein structural and functional properties. Tissue accumulation of carbamylation-derived products and their role in pathological processes such as atherosclerosis or chronic renal failure have been previously documented. However, few studies have focused on the carbamylation of intracellular proteins and their subsequent role in cellular aging. This study aimed to determine the extent of intracellular protein carbamylation, its impact on cell functions and the ability of cells to degrade these modified proteins. Fibroblasts were incubated with cyanate or urea and the carbamylation level was evaluated by immunostaining and homocitrulline quantification. The results showed that carbamylated proteins accumulated intracellularly and that all proteins were susceptible. The presence of intracellular carbamylated proteins did not modify cell proliferation or type I collagen synthesis nor did it induce cell senescence, but it significantly decreased cell motility. Fibroblasts were able to degrade carbamylated proteins through the ubiquitin-proteasome system. In conclusion, intracellular proteins are susceptible to carbamylation but their accumulation does not seem to deeply affect cell function, owing largely to their elimination by the ubiquitin-proteasome system.