Effect of glucose on the biomechanical function of arterial elastin

Age-related changes in the biochemical composition of the human aorta and their correlation with the delamination strength

Various studies have correlated the mechanical properties of the aortic wall with its biochemical parameters and inner structure. Very few studies have addressed correlations with the cohesive properties, which are crucial for understanding fracture phenomena such as aortic dissection, i.e. a life-threatening process. Aimed at filling this gap, we conducted a comprehensive biochemical and histological analysis of human aortas (the ascending and descending thoracic and infrarenal abdominal aorta) from 34 cadavers obtained post-mortem during regular autopsies. The pentosidine, hydroxyproline and calcium contents, calcium/phosphorus molar ratio, degree of atherosclerosis, area fraction of elastin, collagen type I and III, alpha smooth muscle actin, vasa vasorum, vasa vasorum density, aortic wall thickness, thicknesses of the adventitia, media and intima were determined and correlated with the delamination forces in the longitudinal and circumferential directions of the vessel as determined from identical cadavers. The majority of the parameters determined did not indicate significant correlation with age, except for the calcium content and collagen maturation (enzymatic crosslinking). The main results concern differences between enzymatic and non-enzymatic crosslinking and those caused by the presence of atherosclerosis. The enzymatic crosslinking of collagen increased with age and was accompanied by a decrease in the delamination strength, while non-enzymatic crosslinking tended to decrease with age and was accompanied by an increase in the delamination strength. As the rate of calcification increased, the presence of atherosclerosis led to the formation of calcium phosphate plaques with higher solubility than the tissue without or with only mild signs of atherosclerosis. STATEMENT OF SIGNIFICANCE: This study presents a detailed biochemical and histological analysis of human aortic samples (ascending thoracic aorta, descending thoracic aorta and infrarenal abdominal aorta) taken from 34 cadavers. The contribution of this scientific study lies in the detailed biochemical comparison of the enzymatic and non-enzymatic glycosylation-derived crosslinks of vascular tissues and their influence on the delamination strength of the human aorta since, to the best of our knowledge, no such comprehensive studies exist in the literature. A further benefit concerns the notification of the limitations of the various analytical methods applied; an important factor that must be taken into account in such studies.

External Scaffold for Strengthening the Pulmonary Autograft in the Ross Procedure

Despite offering several potential benefits over standard prosthetic aortic valve replacement, the use of the pulmonary autograft has been limited to date due to concerns over the risk of pulmonary autograft expansion and the need for reintervention. Several techniques using materials with biomimetic potential have been developed to reduce this complication. The incidence, risk factors, and pathophysiology of pulmonary autograft dilatation are discussed in this article. This seminar will provide an overview of the techniques of external pulmonary autograft support and their advantages and limitations. It also considers future directions for further investigation and future clinical applications of external pulmonary autograft support. Dilatation of the autograft is more likely to occur in patients with aortic regurgitation and a dilated aortic annulus. External scaffolding may prevent autograft stretching and expansion in these specific cases. However, from a biomimetic point of view, any permanent scaffold potentially restricts the movement of the autograft root. This reduces some of the benefits associated with the use of autologous tissue, which is the priority of the Ross procedure. To address this issue, several bioresorbable matrices could be used to support the root during its initial adaptive phase. Control of blood pressure with aggressive therapy is the first line to avoid this problem in the first year after pulmonary autograft implantation, together with support of the annular and sinotubular junction in some selected cases. This is the best way to maintain stable autograft root dimensions while preserving root dynamics. However, to determine the efficacy of this combined external support and best medical management, it is important to perform regular imaging and clinical follow-up.

Changes in carotid arterial wall viscosity and carotid arterial stiffness in type 2 diabetes patients

BACKGROUND AND AIMS

Changes in arterial wall viscosity (AWW) and stiffness during type 2 diabetes (T2D) have been little investigated. We explored changes in carotid AWV considering change in arterial stiffness and loading conditions, in patients with T2D.

METHODS

This cross-sectional, monocentric study compared 19 middle-aged patients with T2D to 30 non-diabetic (ND) controls. The absolute viscosity (WV) was determined as the area of the pressure-lumen cross-sectional area (P-LCSA) loop obtained by carotid tonometry and contralateral echo-tracking. The relative viscosity was determined as the ratio between WV and the elastic energy stored within the arterial wall (WV/WE). Carotid geometry, midwall stress, distensibility and elastic modulus were also compared between groups.

RESULTS

T2D patients were older and more frequently had hypertension. Internal diameter, mean central and pulse blood pressure were higher in T2D patients but midwall stress was similar compared to ND controls. WV and WV/WE were higher in T2D patients when compared with ND controls (23 [16-41] vs. 11 [7-18] mm Hg.mm2, p=0.007 and 21% [17-25] vs. 12% [8-17], p < 0.001 respectively) even after adjustment on confounding factors. Carotid arterial stiffness was higher in T2D patients, but after adjustment this difference was only observed for the highest levels of midwall stress.

CONCLUSIONS

Carotid AWV and stiffness are increased in T2D patients but only AWV is significantly increased after considering loading conditions. Whether this increase in energy dissipation within the arterial wall contributes to alter cardiovascular coupling in T2D remains to be established.

Perception and response of skeleton to mechanical stress

Mechanical stress stands as a fundamental factor in the intricate processes governing the growth, development, morphological shaping, and maintenance of skeletal mass. The profound influence of stress in shaping the skeletal framework prompts the assertion that stress essentially births the skeleton. Despite this acknowledgment, the mechanisms by which the skeleton perceives and responds to mechanical stress remain enigmatic. In this comprehensive review, our scrutiny focuses on the structural composition and characteristics of sclerotin, leading us to posit that it serves as the primary structure within the skeleton responsible for bearing and perceiving mechanical stress. Furthermore, we propose that osteocytes within the sclerotin emerge as the principal mechanical-sensitive cells, finely attuned to perceive mechanical stress. And a detailed analysis was conducted on the possible transmission pathways of mechanical stress from the extracellular matrix to the nucleus.

Directed Assembly of Elastic Fibers via Coacervate Droplet Deposition on Electrospun Templates

Elastic fibers provide critical elasticity to the arteries, lungs, and other organs. Elastic fiber assembly is a process where soluble tropoelastin is coacervated into liquid droplets, cross-linked, and deposited onto and into microfibrils. While much progress has been made in understanding the biology of this process, questions remain regarding the timing of interactions during assembly. Furthermore, it is unclear to what extent fibrous templates are needed to guide coacervate droplets into the correct architecture. The organization and shaping of coacervate droplets onto a fiber template have never been previously modeled or employed as a strategy for shaping elastin fiber materials. Using an in vitro system consisting of elastin-like polypeptides (ELPs), genipin cross-linker, electrospun polylactic-co-glycolic acid (PLGA) fibers, and tannic acid surface coatings for fibers, we explored ELP coacervation, cross-linking, and deposition onto fiber templates. We demonstrate that integration of coacervate droplets into a fibrous template is primarily influenced by two factors: (1) the balance of coacervation and cross-linking and (2) the surface energy of the fiber templates. The success of this integration affects the mechanical properties of the final fiber network. Our resulting membrane materials exhibit highly tunable morphologies and a range of elastic moduli (0.8-1.6 MPa) comparable to native elastic fibers.

Structural and Mechanical Properties of Human Superficial Femoral and Popliteal Arteries

The femoropopliteal artery (FPA) is the main artery in the lower limb. It supplies blood to the leg muscles and undergoes complex deformations during limb flexion. Atherosclerotic disease of the FPA (peripheral arterial disease, PAD) is a major public health burden, and despite advances in surgical and interventional therapies, the clinical outcomes of PAD repairs continue to be suboptimal, particularly in challenging calcified lesions and biomechanically active locations. A better understanding of human FPA mechanical and structural characteristics in relation to age, risk factors, and the severity of vascular disease can help develop more effective and longer-lasting treatments through computational modeling and device optimization. This review aims to summarize recent research on the main biomechanical and structural properties of human superficial femoral and popliteal arteries that comprise the FPA and describe their anatomy, composition, and mechanical behavior under different conditions.

Dental pulp stones and their correlation with metabolic diseases

Background

Dental pulp calcifications or pulp stones are calcified structures found in dental pulp, mostly around or enclosing a blood vessel. The formation of these calcifications begins with concentric layers of calcified tissue within which remnants of necrotic and calcified cells may be present. The calcifications of thrombi in blood vessels, called phleboliths, may also serve as nidi for denticles. In metabolic diseases such as diabetes, hypertension or poor periodontal health, there are obvious changes in blood vessels and vascularization. In our study, we observed histopathological sections of dental pulp and correlated systemic diseases such as diabetes and hypertension with poor periodontal health and dental pulp stones.

Aim

The aim of our study was to evaluate the histopathology of dental pulp stones, their distribution among various age groups and sexes and to identify any correlations between pulp stone formation and systemic diseases such as type II diabetes and hypertension.

Materials and Methods

Samples from 100 patients with metabolic diseases such as type II diabetes and hypertension were collected. The pulp was extirpated from the teeth that were undergoing root canal treatment, and the teeth were extracted. The collected pulp sample was fixed in 10% formaline neutral buffer, subjected to routine histopathological procedures and stained with haematoxylin and eosin. The pulp of teeth extracted for orthodontic treatment was considered a control for patients with no metabolic disease.

Results

There was a definite relationship between increased pulp stones and metabolic diseases such as type II diabetes and hypertension; likewise, poor periodontal health was significantly related to pulp stones.

Mechanical, structural, and physiologic differences between above and below-knee human arteries

Peripheral Artery Disease (PAD) affects the lower extremities and frequently results in poor clinical outcomes, especially in the vessels below the knee. Understanding the biomechanical and structural characteristics of these arteries is important for improving treatment efficacy, but mechanical and structural data on tibial vessels remain limited. We compared the superficial femoral (SFA) and popliteal (PA) arteries that comprise the above-knee femoropopliteal (FPA) segment to the infrapopliteal (IPA) anterior tibial (AT), posterior tibial (PT), and fibular (FA) arteries from the same 15 human subjects (average age 52, range 42-67 years, 87 % male). Vessels were imaged using μCT, evaluated with biaxial mechanical testing and constitutive modeling, and assessed for elastin, collagen, smooth muscle cells (SMCs), and glycosaminoglycans (GAGs). IPAs were more often diseased or calcified compared to the FPAs. They were also twice smaller, 53 % thinner, and significantly stiffer than the FPA longitudinally, but not circumferentially. IPAs experienced 48 % higher physiologic longitudinal stresses (62 kPa) but 27 % lower circumferential stresses (24 kPa) and similar cardiac cycle stretch of <1.02 compared to the FPA. IPAs had lower longitudinal pre-stretch (1.12) than the FPAs (1.29), but there were no differences in the stored elastic energy during pulsation. The physiologic circumferential stiffness was similar in the above and below-knee arteries (718 kPa vs 754 kPa). Structurally, IPAs had less elastin, collagen, and GAGs than the FPA, but maintained similar SMC content. Our findings contribute to a better understanding of segment-specific human lower extremity artery biomechanics and may inform the development of better medical devices for PAD treatment. STATEMENT OF SIGNIFICANCE: Peripheral Artery Disease (PAD) in the lower extremity arteries exhibits distinct characteristics and results in different clinical outcomes when treating arteries above and below the knee. However, their mechanical, structural, and physiologic differences are poorly understood. Our study compared above- and below-knee arteries from the same middle-aged human subjects and demonstrated distinct differences in size, structure, and mechanical properties, leading to variations in their physiological behavior. These insights could pave the way for creating location-specific medical devices and treatments for PAD, offering a more effective approach to its management. Our findings provide new, important perspectives for clinicians, researchers, and medical device developers interested in treating PAD in both above- and below-knee locations.

Glycation promotes pulp calcification in Type 2 diabetes rat model

OBJECTIVES

Intrapulpal calcifications can occur in the dental pulp of patients with diabetes. We focused on the association between ectopic calcifications in the dental pulp and advanced glycation end products (AGEs) in Spontaneously Diabetic Torii (SDT)-fatty rats, an obese type 2 diabetic rat model, to determine the mechanism of calcification with pulp stone in the dental pulp.

MATERIALS AND METHODS

Pathologic calcification in the dental pulp of SDT-fatty rats was observed using electron microscopy and immunohistochemical analysis. Moreover, mechanical analysis of periapical region of molar tooth against occlusal force was performed.

RESULTS

In SDT-fatty rats, pathogenic pulpal calcifications occurred during blood glucose elevation after 6 weeks, and granular calcification was observed in the dental pulp after 11 weeks. Pentosidine, a major AGE, and the receptor for AGEs were strongly expressed in the dental pulp of SDT-fatty rats. S100A8, TNF-α, and IL-6 also showed positive response in the dental pulp of the SDT-fatty rat, which indicated pulpal inflammation. Blood flow disorder and hypoxic dental pulp cells were also observed. In silico simulation, strain from occlusal force concentrates on the root apex.

CONCLUSIONS

Glycation makes blood vessels fragile, and occlusal forces damage the vessels mechanically. These are factors for intrapulpal calcification of diabetes.

Dill Extract Preserves Dermal Elastic Fiber Network and Functionality: Implication of Elafin

INTRODUCTION

Elastic skin fibers lose their mechanical properties during aging due to enzymatic degradation, lack of maturation, or posttranslational modifications. Dill extract has been observed to increase elastin protein expression and maturation in a 3D skin model, to improve mechanical properties of the skin, to increase elastin protein expression in vascular smooth muscle cells, to preserve aortic elastic lamella, and to prevent glycation.

OBJECTIVE

The aim of the study was to highlight dill actions on elastin fibers during aging thanks to elastase digestion model and the underlying mechanism.

METHODS

In this study, elastic fibers produced by dermal fibroblasts in 2D culture model were injured by elastase, and we observed the action of dill extract on elastic network by elastin immunofluorescence. Then action of dill extract was examined on mice skin by injuring elastin fibers by intradermal injection of elastase. Then elastin fibers were observed by second harmonic generation microscopy, and their functionality was evaluated by oscillatory shear stress tests. In order to understand mechanism by which dill acted on elastin fibers, enzymatic tests and real-time qPCR on cultured fibroblasts were performed.

RESULTS

We evidence in vitro that dill extract is able to prevent elastin from elastase digestion. And we confirm in vivo that dill extract treatment prevents elastase digestion, allowing preservation of the cutaneous elastic network in mice and preservation of the cutaneous elastic properties. Although dill extract does not directly inhibit elastase activity, our results show that dill extract treatment increases mRNA expression of the endogenous inhibitor of elastase, elafin.

CONCLUSION

Dill extract can thus be used to counteract the negative effects of elastase on the cutaneous elastic fiber network through modulation of PI3 gene expression.

Assessment of the obesity based on voice perception

Human voice is an extremely important biological signal which contains information about sex, age, emotional state, health and physical features of a speaker. Estimating a physical appearance from a vocal cue can be an important asset for sciences including forensics and dietetics. Although there have been several studies focused on the relationships between vocal parameters and ratings of height, weight, age and musculature of a speaker, to our knowledge, there has not been a study examining the assessment of one’s BMI based on voice alone. The purpose of the current study was to determine the ability of female “Judges” to evaluate speakers’ (men and women) obesity and body fat distribution from their vocal cues. It has also been checked which voice parameters are key vocal cues in this assessment. The study material consisted of 12 adult speakers’ (6 women) voice recordings assessed by 87 “Judges” based on a 5-point graphic scale presenting body fat level and distribution (separately for men and women). For each speaker body height, weight, BMI, Visceral Fat Level (VFL, InBody 270) and acoustic parameters were measured. In addition, the accuracy of BMI category was verified. This study also aimed to determine which vocal parameters were cues for the assessment for men and women. To achieve it, two independent experiments were conducted: I: “Judges” had to choose one (obese) speaker from 3 voices (in 4 series); II: they were asked to rate body fat level of the same 12 speakers based on 5-point graphic scale. Obese speakers (i.e., BMI above 30) were selected correctly with the accuracy greater than predicted by chance (experiment I). By using a graphic scale, our study found that speakers exhibiting higher BMI were rated as fatter (experiment II). For male speakers the most important vocal predictors of the BMI were harmonics-to-noise ratio (HNR) and formant dispersion (Df); for women: formant spacing (Pf) and intensity (loudness). Human voice contains information about one’s increased BMI level which are hidden in some vocal cues.

Changes in elastin structure and extensibility induced by hypercalcemia and hyperglycemia

Elastin is a key elastomeric protein responsible for the elasticity of many organs, including heart, skin, and blood vessels. Due to its intrinsic long life and low turnover rate, damage in elastin induced by pathophysiological conditions, such as hypercalcemia and hyperglycemia, accumulates during biological aging and in aging-associated diseases, such as diabetes mellitus and atherosclerosis. Prior studies have shown that calcification induced by hypercalcemia deteriorates the function of aortic tissues. Glycation of elastin is triggered by hyperglycemia and associated with elastic tissue damage and loss of mechanical functions via the accumulation of advanced glycation end products. To evaluate the effects on elastin's structural conformations and elasticity by hypercalcemia and hyperglycemia at the molecular scale, we perform classical atomistic and steered molecular dynamics simulations on tropoelastin, the soluble precursor of elastin, under different conditions. We characterize the interaction sites of glucose and calcium and associated structural conformational changes. Additionally, we find that elevated levels of calcium ions and glucose hinder the extensibility of tropoelastin by rearranging structural domains and altering hydrogen bonding patterns, respectively. Overall, our investigation helps to reveal the behavior of tropoelastin and the biomechanics of elastin biomaterials in these physiological environments. STATEMENT OF SIGNIFICANCE: Elastin is a key component of elastic fibers which endow many important tissues and organs, from arteries and veins, to skin and heart, with strength and elasticity. During aging and aging-associated diseases, such as diabetes mellitus and atherosclerosis, physicochemical stressors, including hypercalcemia and hyperglycemia, induce accumulated irreversible damage in elastin, and consequently alter mechanical function. Yet, molecular mechanisms associated with these processes are still poorly understood. Here, we present the first study on how these changes in elastin structure and extensibility are induced by hypercalcemia and hyperglycemia at the molecular scale, revealing the essential roles that calcium and glucose play in triggering structural alterations and mechanical stiffness. Our findings yield critical insights into the first steps of hypercalcemia- and hyperglycemia-mediated aging.

Biomechanical Properties of Mouse Carotid Arteries With Diet-Induced Metabolic Syndrome and Aging

Metabolic syndrome increases the risk of cardiovascular diseases. Arteries gradually stiffen with aging; however, it can be worsened by the presence of conditions associated with metabolic syndrome. In this study, we investigated the combined effects of diet-induced metabolic syndrome and aging on the biomechanical properties of mouse common carotid arteries (CCA). Male mice at 2 months of age were fed a normal or a high fat and high sucrose (HFHS) diet for 2 (young group), 8 (adult group) and 18-20 (old group) months. CCAs were excised and subjected to in vitro biaxial inflation-extension tests and the Cauchy stress-stretch relationships were determined in both the circumferential and longitudinal directions. The elastic energy storage of CCAs was obtained using a four-fiber family constitutive model, while the material stiffness in the circumferential and longitudinal directions was computed. Our study showed that aging is a dominant factor affecting arterial remodeling in the adult and old mice, to a similar extent, with stiffening manifested with a significantly reduced capability of energy storage by ∼50% (p < 0.05) and decreases in material stiffness and stress (p < 0.05), regardless of diet. On the other hand, high fat high sucrose diet resulted in an accelerated arterial remodeling in the young group at pre-diabetic stage by affecting the circumferential material stiffness and stress (p < 0.05), which was eventually overshadowed by aging progression. These findings have important implications on the effects of metabolic syndrome on elastic arteries in the younger populations.

Effect of intracanal and extracanal heating on pulp dissolution property of continuous chelation irrigant

Context

Extracanal and intracanal heating of sodium hypochlorite (NaOCl) improve its pulp dissolution, but limited literature is available on its effect as a combined single irrigant with etidronate.

Aim

The aim of this study is to compare the effect of temperature on the effectiveness of NaOCl and continuous chelation protocol on the time required for the dissolution of vital and necrotic pulp.

Materials and Methods

Dissolution time of 120 standardized bovine (buffalo) pulp fragments, divided into 12 subgroups based on tissue type (vital/necrotic), irrigant (NaOCl/continuous chelation), and temperature (extracanal, intracanal, and nonheated irrigant), was noted. Conical glass tips mimicking the root canal were considered specimen containers. About 0.2 ml of irrigant corresponding to the irrigation protocol was taken in them and then pulp samples were added to it. Samples were observed using loupes under 2.5 X magnification. Dissolution time was recorded using a stopwatch. The study was approved by the Institutional Ethical Committee (SDC/2019/591).

Statistical Analysis Used

Two-way analysis of variance; statistical product and service solutions version 25. The level of significance was set at P < 0.05.

Results

Time for pulp dissolution by continuous chelation mixture was significantly more as compared to NaOCl alone in all subgroups. Pulp tissue dissolution for both vital and necrotic pulp was improved by the increase in temperature of both irrigants and dissolution time was more for necrotic than vital tissue. Pulp tissue dissolution was significantly better by intracanal heating as compared to extracanal heating.

Conclusion

Although intracanal heating of continuous chelation mixture improves its pulp dissolution capacity significantly as compared to extracanal heating and nonheating protocol but pulpal dissolution capacity of nonheated 5% NaOCl still remains significantly better as compared to intracanal and extracanal heated continuous chelation mixture.

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.

Clinical Relevance of Elastin in the Structure and Function of Skin

Elastin is the main component of elastic fibers, which provide stretch, recoil, and elasticity to the skin. Normal levels of elastic fiber production, organization, and integration with other cutaneous extracellular matrix proteins, proteoglycans, and glycosaminoglycans are integral to maintaining healthy skin structure, function, and youthful appearance. Although elastin has very low turnover, its production decreases after individuals reach maturity and it is susceptible to damage from many factors. With advancing age and exposure to environmental insults, elastic fibers degrade. This degradation contributes to the loss of the skin's structural integrity; combined with subcutaneous fat loss, this results in looser, sagging skin, causing undesirable changes in appearance. The most dramatic changes occur in chronically sun-exposed skin, which displays sharply altered amounts and arrangements of cutaneous elastic fibers, decreased fine elastic fibers in the superficial dermis connecting to the epidermis, and replacement of the normal collagen-rich superficial dermis with abnormal clumps of solar elastosis material. Disruption of elastic fiber networks also leads to undesirable characteristics in wound healing, and the worsening structure and appearance of scars and stretch marks. Identifying ways to replenish elastin and elastic fibers should improve the skin's appearance, texture, resiliency, and wound-healing capabilities. However, few therapies are capable of repairing elastic fibers or substantially reorganizing the elastin/microfibril network. This review describes the clinical relevance of elastin in the context of the structure and function of healthy and aging skin, wound healing, and scars and introduces new approaches being developed to target elastin production and elastic fiber formation.

Failure Properties of Healthy and Diabetic Rabbit Thoracic Aortas and Their Potential Correlation with Mass Fractions of Collagen

PURPOSE

Diabetes Mellitus (DM) plays an important role in aortic remodeling and alters the wall mechanics. The purpose of this study is to investigate and compare multi-directional failure properties of healthy and diabetic thoracic aortas.

METHODS

Thirty adult rabbits (1.6-2.2 kg) were collected and type 1 diabetic rabbit model was induced by injection of alloxan. A total of 10 control and 20 diabetic (with different time exposure to diabetic condition) rabbit descending thoracic aortas were harvested. Uniaxial tensile (UT) and radial tension (RT) tests were performed to determine circumferential, axial and radial failure stresses of the control and diabetic aortas, which were further correlated with mass fractions (MFs) of collagen.

RESULTS

Throughout the UT test, there was a clear indication of anisotropic mechanical responses for some diabetic aorta specimens in the high loading domain. There was a trend towards an increase in the mean circumferential and axial failure stresses for the diabetic aortas when compared to the control aortas. However, differences were not statistically significant. The quantified failure stresses in the circumferential direction were, in general, higher than the stress values in the axial direction for both control and diabetic groups. For the RT test, the radial failure stresses of the diabetic aortas (in 8 weeks) were significantly higher than those of the control aortas (95 ± 17 vs. 63 ± 15 kPa, p = 0.01). Strong correlations were identified between the circumferential failure stresses and the MFs of collagen for both control and diabetic aortas. Nevertheless, this correlation was not present in the axial and radial directions.

CONCLUSION

The results suggest that there is a lower propensity of radial tear occurrence within the diabetic aortic wall. More importantly, time exposure to diabetic condition is not a factor that may change failure properties of the rabbit descending thoracic aortas in the circumferential and axial directions.

A guide to the composition and functions of the extracellular matrix

Extracellular matrix (ECM) is a dynamic 3-dimensional network of macromolecules that provides structural support for the cells and tissues. Accumulated knowledge clearly demonstrated over the last decade that ECM plays key regulatory roles since it orchestrates cell signaling, functions, properties and morphology. Extracellularly secreted as well as cell-bound factors are among the major members of the ECM family. Proteins/glycoproteins, such as collagens, elastin, laminins and tenascins, proteoglycans and glycosaminoglycans, hyaluronan, and their cell receptors such as CD44 and integrins, responsible for cell adhesion, comprise a well-organized functional network with significant roles in health and disease. On the other hand, enzymes such as matrix metalloproteinases and specific glycosidases including heparanase and hyaluronidases contribute to matrix remodeling and affect human health. Several cell processes and functions, among them cell proliferation and survival, migration, differentiation, autophagy, angiogenesis, and immunity regulation are affected by certain matrix components. Structural alterations have been also well associated with disease progression. This guide on the composition and functions of the ECM gives a broad overview of the matrisome, the major ECM macromolecules, and their interaction networks within the ECM and with the cell surface, summarizes their main structural features and their roles in tissue organization and cell functions, and emphasizes the importance of specific ECM constituents in disease development and progression as well as the advances in molecular targeting of ECM to design new therapeutic strategies.

Effect of Glycation on Interlamellar Bonding of Arterial Elastin

BACKGROUND

Interlamellar bonding in the arterial wall is often compromised by cardiovascular diseases. However, several recent nationwide and hospital-based studies have uniformly reported reduced risk of thoracic aortic dissection in patients with diabetes. As one of the primary structural constituents in the arterial wall, elastin plays an important role in providing its interlamellar structural integrity.

OBJECTIVE

The purpose of this study is to examine the effects of glycation on the interlamellar bonding properties of arterial elastin.

METHODS

Purified elastin network was isolated from porcine descending thoracic aorta and incubated in 2 M glucose solution for 7, 14 or 21 days at 37 °C. Peeling and direct tension tests were performed to provide complimentary information on understanding the interlamellar layer separation properties of elastin network with glycation effect. Peeling tests were simulated using a cohesive zone model (CZM). Multiphoton imaging was used to visualize the interlamellar elastin fibers in samples subjected to peeling and direct tension.

RESULTS

Peeling and direct tension tests show that interlamellar energy release rate and strength both increases with the duration of glucose treatment. The traction at damage initiation estimated for the CZM agrees well with the interlamellar strength measurements from direct tension tests. Glycation was also found to increase the interlamellar failure strain of arterial elastin. Multiphoton imaging confirmed the contribution of radially running elastin fibers to resisting dissection.

CONCLUSIONS

Nonenzymatic glycation reduces the propensity of arterial elastin to dissection. This study also suggests that the CZM effectively describes the interlamellar bonding properties of arterial elastin.

Mechanical and structural contributions of elastin and collagen fibers to interlamellar bonding in the arterial wall

The artery relies on interlamellar structural components, mainly elastin and collagen fibers, for maintaining its integrity and resisting dissection propagation. In this study, the contribution of arterial elastin and collagen fibers to interlamellar bonding was studied through mechanical testing, multiphoton imaging and finite element modeling. Steady-state peeling experiments were performed on porcine aortic media and the purified elastin network in the circumferential (Circ) and longitudinal (Long) directions. The peeling force and energy release rate associated with mode-I failure are much higher for aortic media than for the elastin network. Also, longitudinal peeling exhibits a higher energy release rate and strength than circumferential peeling for both the aortic media and elastin. Multiphoton imaging shows the recruitment of both elastin and collagen fibers within the interlamellar space and points to in-plane anisotropy of fiber distributions as a potential mechanism for the direction-dependent phenomena of peeling tests. Three-dimensional finite element models based on cohesive zone model (CZM) of fracture were created to simulate the peeling tests with the interlamellar energy release rate and separation distance at damage initiation obtained directly from peeling test. Our experimental results show that the separation distance at damage initiation is 80 μm for aortic media and 40 μm for elastin. The damage initiation stress was estimated from the model for aortic media (Circ: 60 kPa; Long: 95 kPa) and elastin (Circ: 9 kPa; Long: 14 kPa). The interlamellar separation distance at complete failure was estimated to be 3 - 4 mm for both media and elastin. Furthermore, elastin and collagen fibers both play an important role in bonding of the arterial wall, while collagen has a higher contribution than elastin to interlamellar stiffness, strength and toughness. These results on microstructural interlamellar failure shed light on the pathological development and progression of aortic dissection.

Glucose-induced structural changes and anomalous diffusion of elastin

Elastin is the principal protein component of elastic fiber, which renders essential elasticity to connective tissues and organs. Here, we adopted a multi-technique approach to study the transport, viscoelastic, and structural properties of elastin exposed to various glucose concentrations (X=[gluc]/[elastin]). Laser light scattering experiments revealed an anomalous behavior (anomaly exponent, β <0.6) of elastin. In this regime (β <0.6), the diffusion constant decreases by 40% in the presence of glucose (X> 10), which suggests the structural change in elastin. We have observed a peculiar inverse temperature transition of elastin protein, which is a measure of structural change, at 40 °C through rheology experiments. Moreover, we observe its shift towards lower temperature with a higher X. FTIR revealed that the presence of glucose (X < 10) favors the formation of β-sheet structure in elastin. However, for X > 10, dominative crowding effect reduces the mobility of protein and favors the increase in β-turns and γ-turns by 25 ± 1% over the β-sheet (β-sheet decreases by 12 ± 0.8%) and α-helix (α-helix decreases by 13 ± 0.8%). The stiffness of protein is estimated through Flory characteristic ratio, C_∞ and found to be increasing with X. These glucose-based structural changes in the elastin may explain the role of glucose in age-related issues of the skin.

Effect of diabetes mellitus on the dissection properties of the rabbit descending thoracic aortas

Effect of diabetes mellitus (DM) on the dissection properties of thoracic aortas remains largely unclear and relevant biomechanical analysis is lacking. In the present study forty adult rabbits (1.6-2.2 kg) were collected and type 1 diabetic rabbit model was induced by injection of alloxan. A total of 10 control and 30 diabetic (with different time exposure to diabetic condition) rabbit descending thoracic aortas were harvested. Peeling tests were performed to quantitatively determine force/width values and dissection energy in the control and diabetic aortas. Histological and mass fraction analyses were performed to characterize the dissected morphology and to quantify dry weight percentages of elastin and collagen. The resisting force/width values were significantly higher for the diabetic thoracic aortas (in 8 weeks) than those of the control thoracic aortas (axial: 26.1 ± 4.0 vs. 20.5 ± 3.1 mN/mm, p = 0.04; circ: 19.7 ± 2.8 vs. 15.3 ± 1.9 mN/mm, p = 0.03). There was a higher resistance to the dissection in both axial and circumferential directions for the diabetic aortas. The dissection energy generated by axial and circumferential peeling of the diabetic aortas (in 6 and 8 weeks) was statistically significantly higher than that of the control aortas (axial: 5.6 ± 0.7 vs. 4.3 ± 0.5 mJ/cm², p = 0.02; circ: 3.9 ± 0.3 vs. 3.2 ± 0.3 mJ/cm², p = 0.02). Histology showed that dissection mainly occurred in the aortic media and the dissected surfaces were close to external elastic lamina for some specimens. The mass fractions of collagen within the diabetic aortas increased significantly as compared to the control aortas, whereas no significant change was found for that of elastin. Our data suggest that the experimentally induced DM may lead to a lower propensity of dissection for the rabbit thoracic aortas. The dissection properties of the rabbit thoracic aortas vary with time exposed to diabetic condition.

Mechanical Properties of Arterial Elastin With Water Loss

Elastin is a peculiar elastomer in that it requires water to maintain resilience, and its mechanical properties are closely associated with the immediate aqueous environment. The bulk, extra- and intrafibrillar water plays important roles in both elastic and viscoelastic properties of elastin. In this study, a two-stage liquid-vapor method was developed to investigate the effects of water loss on the mechanical properties of porcine aortic elastin. The tissue samples started in a phosphate-buffered saline (PBS) solution at their fully hydrated condition, with a gravimetric water content of 370±36%. The hydration level was reduced by enclosing the tissue in dialysis tubing and submerging it in polyethylene glycol (PEG) solution at concentrations of 10%, 20%, 30%, and 45% w/v, which reduced the water content of the samples to 258±34%, 224±20%, 109±9%, and 58±3%, respectively. The samples were then transferred to a humidity chamber to maintain the hydration level while the samples underwent equi-biaxial tensile and stress relaxation tests. The concentration of 10% PEG treatment induced insignificant changes in tissue dimensions and stiffness, indicating that the removal of bulk water has less effect on elastin. Significant increases in tangent modulus were observed after 20% and 30% PEG treatment due to the decreased presence of extrafibrillar water. Elastin treated with 45% PEG shows a very rigid behavior as most of the extrafibrillar water is eliminated. These results suggest that extrafibrillar water is crucial for elastin to maintain its elastic behavior. It was also observed that the anisotropy of elastin tends to decrease with water loss. An increase in stress relaxation was observed for elastin treated with 30% PEG, indicating a more viscous behavior of elastin when the amount of extrafibrillar water is significantly reduced. Results from this study shed light on the close association between the bulk, extra- and intrafibrillar water pools and the mechanics of elastin.

Role of elastin peptides and elastin receptor complex in metabolic and cardiovascular diseases

The Cardiovascular Continuum describes a sequence of events from cardiovascular risk factors to end-stage heart disease. It includes conventional pathologies affecting cardiovascular functions such as hypertension, atherosclerosis or thrombosis and was traditionally considered from the metabolic point of view. This Cardiovascular Continuum, originally described by Dzau and Braunwald, was extended by O'Rourke to consider also the crucial role played by degradation of elastic fibers, occurring during aging, in the appearance of vascular stiffness, another deleterious risk factor of the continuum. However, the involvement of the elastin degradation products, named elastin-derived peptides, to the Cardiovascular Continuum progression has not been considered before. Data from our laboratory and others clearly showed that these bioactive peptides are central regulators of this continuum, thereby amplifying appearance and evolution of cardiovascular risk factors such as diabetes or hypertension, of vascular alterations such as atherothrombosis and calcification, but also nonalcoholic fatty liver disease and nonalcoholic steatohepatitis. The Elastin Receptor Complex has been shown to be a crucial actor in these processes. We propose here the participation of these elastin-derived peptides and of the Elastin Receptor Complex in these events, and introduce a revisited Cardiovascular Continuum based on their involvement, for which elastin-based pharmacological strategies could have a strong impact in the future.

Proinflammatory Arterial Stiffness Syndrome: A Signature of Large Arterial Aging

Age-associated structural and functional remodeling of the arterial wall produces a productive environment for the initiation and progression of hypertension and atherosclerosis. Chronic aging stress induces low-grade proinflammatory signaling and causes cellular proinflammation in arterial walls, which triggers the structural phenotypic shifts characterized by endothelial dysfunction, diffuse intimal-medial thickening, and arterial stiffening. Microscopically, aged arteries exhibit an increase in arterial cell senescence, proliferation, invasion, matrix deposition, elastin fragmentation, calcification, and amyloidosis. These characteristic cellular and matrix alterations not only develop with aging but can also be induced in young animals under experimental proinflammatory stimulation. Interestingly, these changes can also be attenuated in old animals by reducing low-grade inflammatory signaling. Thus, mitigating age-associated proinflammation and arterial phenotype shifts is a potential approach to retard arterial aging and prevent the epidemic of hypertension and atherosclerosis in the elderly.

Distribution of tightly and loosely bound water in biological macromolecules and age-related diseases

This mini-review article is focused on publications devoted to the changes in water binding energy and content of bound water in biological tissues during aging processes, when bound water lost from the hydration layer becomes free water. Bound water is released during cataractogenesis. In skin, water bound to proteins and other biomacromolecules becomes more mobile with increasing skin age. Extracellular to intracellular water ratio increases with age and was associated with muscle cell atrophy. Bound water concentration decreases with age in hydrated human bone and can be correlated with the strength and toughness of the bone. Higher fraction of free water in malignant tissues compared to normal tissues was observed. Hydration water mobility is enhanced around tau amyloid fibers. Water plays a decisive role in amyloid formation as entropic driving force. In the natural aging processes dehydration and glycation may be considered as subsequent steps.

Elastin, arterial mechanics, and cardiovascular disease

Large, elastic arteries are composed of cells and a specialized extracellular matrix that provides reversible elasticity and strength. Elastin is the matrix protein responsible for this reversible elasticity that reduces the workload on the heart and dampens pulsatile flow in distal arteries. Here, we summarize the elastin protein biochemistry, self-association behavior, cross-linking process, and multistep elastic fiber assembly that provide large arteries with their unique mechanical properties. We present measures of passive arterial mechanics that depend on elastic fiber amounts and integrity such as the Windkessel effect, structural and material stiffness, and energy storage. We discuss supravalvular aortic stenosis and autosomal dominant cutis laxa-1, which are genetic disorders caused by mutations in the elastin gene. We present mouse models of supravalvular aortic stenosis, autosomal dominant cutis laxa-1, and graded elastin amounts that have been invaluable for understanding the role of elastin in arterial mechanics and cardiovascular disease. We summarize acquired diseases associated with elastic fiber defects, including hypertension and arterial stiffness, diabetes, obesity, atherosclerosis, calcification, and aneurysms and dissections. We mention animal models that have helped delineate the role of elastic fiber defects in these acquired diseases. We briefly summarize challenges and recent advances in generating functional elastic fibers in tissue-engineered arteries. We conclude with suggestions for future research and opportunities for therapeutic intervention in genetic and acquired elastinopathies.

Mechanical Characterization and Material Modeling of Diabetic Aortas in a Rabbit Model

Diabetes has been recognized as a major risk factor to cause macrovascular diseases and plays a key role in aortic wall remodeling. However, the effects of diabetes on elastic properties of aortas remain largely unknown and quantitative mechanical data are lacking. Thirty adult rabbits (1.6-2.2 kg) were collected and the type 1 diabetic rabbit model was induced by injection of alloxan. A total of 15 control and 15 diabetic rabbit (abdominal) aortas were harvested. Uniaxial and biaxial tensile tests were performed to measure ultimate tensile strength and to characterize biaxial mechanical behaviors of the aortas. A material model was fitted to the biaxial experimental data to obtain constitutive parameters. Histological and mass fraction analyses were performed to investigate the underlying microstructure and dry weight percentages of elastin and collagen in the control and the diabetic aortas. No statistically significant difference was found in ultimate tensile strength between the control and the diabetic aortas. Regarding biaxial mechanical responses, the diabetic aortas exhibited significantly lower extensibility and significantly higher tissue stiffness than the control aortas. Notably, tissue stiffening occurred in both circumferential and axial directions for the diabetic aortas; however, mechanical anisotropy does not change significantly. The material model was able to fit biaxial experimental data very well. Histology showed that a number of isolated foam cells were embedded in the diabetic aortas and hyperplasia of collagen was identified. The dry weight percentages of collagen within the diabetic aortas increased significantly as compared to the control aortas, whereas no significant change was found for that of elastin. Our data suggest that the diabetes impairs elastic properties and alters microstructure of the aortas and consequently, these changes may further contribute to complex aortic wall remodeling.

The Coupled Bio-Chemo-Electro-Mechanical Behavior of Glucose Exposed Arterial Elastin

Elastin, the principle protein component of the elastic fiber, is a critical extracellular matrix (ECM) component of the arterial wall providing structural resilience and biological signaling essential in vascular morphogenesis and maintenance of mechanical homeostasis. Pathogenesis of many cardiovascular diseases have been associated with alterations of elastin. As a long-lived ECM protein that is deposited and organized before adulthood, elastic fibers can suffer from cumulative effects of biochemical exposure encountered during aging and/or disease, which greatly compromise their mechanical function. This review article covers findings from recent studies of the mechanical and structural contribution of elastin to vascular function, and the effects of biochemical degradation. Results from diverse experimental methods including tissue-level mechanical characterization, fiber-level nonlinear optical imaging, piezoelectric force microscopy, and nuclear magnetic resonance are reviewed. The intriguing coupled bio-chemo-electro-mechanical behavior of elastin calls for a multi-scale and multi-physical understanding of ECM mechanics and mechanobiology in vascular remodeling.

Mechanical, structural, and dynamical modifications of cholesterol exposed porcine aortic elastin

Elastin is a protein of the extracellular matrix that contributes significantly to the elasticity of connective tissues. In this study, we examine dynamical and structural modifications of aortic elastin exposed to cholesterol by NMR spectroscopic and relaxation methodologies. Macroscopic measurements are also presented and reveal that cholesterol treatment may cause a decrease in the stiffness of tissue. ²H NMR relaxation techniques revealed differences between the relative populations of water that correlate with the swelling of the tissue following cholesterol exposure. ¹³C magic-angle-spinning NMR spectroscopy and relaxation methods indicate that cholesterol treated aortic elastin is more mobile than control samples. Molecular dynamics simulations on a short elastin repeat VPGVG in the presence of cholesterol are used to investigate the energetic and entropic contributions to the retractive force, in comparison to the same peptide in water. Peptide stiffness is observed to reduce following cholesterol exposure due to a decrease in the entropic force.

Multi-scale Modeling of the Cardiovascular System: Disease Development, Progression, and Clinical Intervention

Cardiovascular diseases (CVDs) are the leading cause of death in the western world. With the current development of clinical diagnostics to more accurately measure the extent and specifics of CVDs, a laudable goal is a better understanding of the structure-function relation in the cardiovascular system. Much of this fundamental understanding comes from the development and study of models that integrate biology, medicine, imaging, and biomechanics. Information from these models provides guidance for developing diagnostics, and implementation of these diagnostics to the clinical setting, in turn, provides data for refining the models. In this review, we introduce multi-scale and multi-physical models for understanding disease development, progression, and designing clinical interventions. We begin with multi-scale models of cardiac electrophysiology and mechanics for diagnosis, clinical decision support, personalized and precision medicine in cardiology with examples in arrhythmia and heart failure. We then introduce computational models of vasculature mechanics and associated mechanical forces for understanding vascular disease progression, designing clinical interventions, and elucidating mechanisms that underlie diverse vascular conditions. We conclude with a discussion of barriers that must be overcome to provide enhanced insights, predictions, and decisions in pre-clinical and clinical applications.