Ageing of the conduit arteries

Age-related intimal stiffening enhances endothelial permeability and leukocyte transmigration

Age is the most significant risk factor for atherosclerosis; however, the link between age and atherosclerosis is poorly understood. During both aging and atherosclerosis progression, the blood vessel wall stiffens owing to alterations in the extracellular matrix. Using in vitro and ex vivo models of vessel wall stiffness and aging, we show that stiffening of extracellular matrix within the intima promotes endothelial cell permeability--a hallmark of atherogenesis. When cultured on hydrogels fabricated to match the elasticity of young and aging intima, endothelial monolayers exhibit increased permeability and disrupted cell-cell junctions on stiffer matrices. In parallel experiments, we showed a corresponding increase in cell-cell junction width with age in ex vivo aortas from young (10 weeks) and old (21 to 25 months) healthy mice. To investigate the mechanism by which matrix stiffening alters monolayer integrity, we found that cell contractility increases with increased matrix stiffness, mechanically destabilizing cell-cell junctions. This increase in endothelial permeability results in increased leukocyte extravasation, which is a critical step in atherosclerotic plaque formation. Mild inhibition of Rho-dependent cell contractility using Y-27632, an inhibitor of Rho-associated kinase, or small interfering RNA restored monolayer integrity in vitro and in vivo. Our results suggest that extracellular matrix stiffening alone, which occurs during aging, can lead to endothelial monolayer disruption and atherosclerosis pathogenesis. Because previous therapeutics designed to decrease vascular stiffness have been met with limited success, our findings could be the basis for the design of therapeutics that target the Rho-dependent cellular contractile response to matrix stiffening, rather than stiffness itself, to more effectively prevent atherosclerosis progression.

Carotid stiffness in young adults: a life-course analysis of its early determinants: the Amsterdam Growth and Health Longitudinal Study

Cardiovascular risk factors affecting arterial stiffness in adulthood may develop at different critical periods earlier in life. We examined whether the trajectories, from adolescence to young adulthood, of blood pressure, body fatness and fat distribution, blood lipids, cardiorespiratory fitness, and heart rate determined levels of arterial stiffness in young adults. We investigated 373 apparently healthy adults in whom cardiovascular risk factors were repeatedly examined between the ages of 13 and 36 years and carotid stiffness estimates were obtained at the age of 36 years. Differences in the mean levels and the trajectories of risk factors throughout the 24-year longitudinal period between subjects with different levels of carotid stiffness at age 36 years were analyzed with generalized estimating equations. Compared with individuals with less stiff carotid arteries, those with stiffer carotid arteries at the age of 36 years were characterized from ages 13 to 36 years by greater levels of and steeper increases in blood pressure and central fatness, independently of each other and other risk factors. These increases were already present in adolescence, preceded the development of poorer levels of blood lipids, cardiorespiratory fitness, and heart rate, which were evident during adulthood only, and explained to a great extent the deleterious association between these risk factors and carotid stiffness at the age of 36 years. Multiple and intertwined mechanisms involved in the pathogenesis of arterial stiffness have their origins in early life. Blood pressure and central fatness have a pivotal role herein and should be specifically targeted to prevent arterial stiffening and its cardiovascular sequelae.

Evolving biaxial mechanical properties of mouse carotid arteries in hypertension

Quantifying the time course of load-induced changes in arterial wall geometry, microstructure, and properties is fundamental to developing mathematical models of growth and remodeling. Arteries adapt to altered pressure and flow by modifying wall thickness, inner diameter, and axial length via marked cell and matrix turnover. To estimate particular biomaterial implications of such adaptations, we used a 4-fiber family constitutive relation to quantify passive biaxial mechanical behaviors of mouse carotid arteries 0 (control), 7-10, 10-14, or 35-56 days after an aortic arch banding surgery that increased pulse pressure and pulsatile flow in the right carotid artery. In vivo circumferential and axial stretches at mean arterial pressure were, for example, 11% and 26% lower, respectively, in hypertensive carotids 35-56 days after banding than in normotensive controls; this finding is consistent with observations that hypertension decreases distensibility. Interestingly, the strain energy W stored in the carotids at individual in vivo conditions was also less in hypertensive compared with normotensive carotids. For example, at 35-56 days after banding, W was 24%, 39%, and 47% of normal values at diastolic, mean, and systolic pressures, respectively. The energy stored during the cardiac cycle, W(sys)-W(dias), also tended to be less, but this reduction did not reach significance. When computed at normal in vivo values of biaxial stretch, however, W was well above normal for the hypertensive carotids. This net increase resulted from an overall increase in the collagen-related anisotropic contribution to W despite a decrease in the elastin-related isotropic contribution. The latter was consistent with observed decreases in the mass fraction of elastin.

Fat mass is inversely associated with serum carboxymethyl-lysine, an advanced glycation end product, in adults

High levels of circulating advanced glycation end products (AGE) are associated with cardiovascular disease, diabetes, chronic kidney disease, and increased mortality, but factors that influence levels of circulating AGE are not well known. Our objective was to characterize the relationship between serum carboxymethyl-lysine (CML), a major circulating AGE, and body composition in adults. In a cross-sectional study, total body DXA was performed and serum CML was measured in 592 adults, aged 26-93 y, from the Baltimore Longitudinal Study of Aging. Median (25th, 75th percentile) CML concentrations were 2.26 (1.86, 2.67) μmol/L. Total fat mass [β = -0.17 (95% CI -0.10, -0.24); P < 0.0001], truncal fat mass [β = -0.17 (95% CI -0.10, -0.25); P < 0.0001], and appendicular fat mass [β = -0.13 (95% CI -0.05, -0.20); P = 0.001] per 1 SD increase were inversely associated with serum CML in separate multivariate linear regression models, adjusting for age, sex, BMI, systolic blood pressure, TG, HDL cholesterol, and renal function. Lean body mass was not independently associated with serum CML. These findings suggest that serum CML concentration is strongly affected by body fat, possibly because CML is preferentially deposited in fat tissue or because adipocytes affect the metabolism of AGE.

Vascular calcification and aortic fibrosis: a bifunctional role for osteopontin in diabetic arteriosclerosis

OBJECTIVE

Calcification and fibrosis reduce vascular compliance in arteriosclerosis. To better understand the role of osteopontin (OPN), a multifunctional protein upregulated in diabetic arteries, we evaluated contributions of OPN in male low-density lipoprotein receptor (LDLR)-/- mice fed a high-fat diet.

METHODS AND RESULTS

OPN had no impact on high-fat diet-induced hyperglycemia, dyslipidemia, or body composition. However, OPN-/-;LDLR-/- mice exhibited an altered time-course of aortic calcium accrual-reduced during initiation but increased with progression-versus OPN+/+;LDLR-/- controls. Collagen accumulation, chondroid metaplasia, and mural thickness were increased in aortas of OPN-/-;LDLR-/- mice. Aortic compliance was concomitantly reduced. Vascular reexpression of OPN (SM22-OPN transgene) reduced aortic Col2A1 and medial chondroid metaplasia but did not affect atherosclerotic calcification, Col1A1 expression, collagen accumulation, or arterial stiffness. Dosing with the proinflammatory OPN fragment SVVYGLR upregulated aortic Wnt and osteogenic gene expression, increased aortic β-catenin, and restored early-phase aortic calcification in OPN-/-;LDLR-/- mice.

CONCLUSIONS

OPN exerts stage-specific roles in arteriosclerosis in LDLR-/- mice. Actions phenocopied by the OPN metabolite SVVYGLR promote osteogenic calcification processes with disease initiation. OPN limits vascular chondroid metaplasia, endochondral mineralization, and collagen accumulation with progression. Complete deficiency yields a net increase in arteriosclerotic disease, reducing aortic compliance and conduit vessel function in LDLR-/- mice.

The effects of 12-week psyllium fibre supplementation or healthy diet on blood pressure and arterial stiffness in overweight and obese individuals

Endothelial dysfunction and increased arterial stiffness occur early in the pathogenesis of the metabolic syndrome and they are both powerful independent predictors of cardiovascular risk. A high-fibre diet has been correlated with lower BMI and a lower incidence of hyperlipidaemia, CVD, hypertension and diabetes. The present randomised, parallel-design study compared the effects of fibre intake from a healthy diet v. fibre supplement diets on blood pressure (BP) and vascular function over 12 weeks. Overweight and obese adults were randomised to one of three groups: control (with placebo), fibre supplement (FIB) or healthy eating group with placebo (HLT). Systolic blood pressure (SBP) was lower in the FIB group compared with the control group at week 6, but not at week 12. However, SBP was lower in the HLT group compared with control group at week 12. At week 6, the FIB group presented lower diastolic blood pressure and augmentation index compared with the control group, but this result did not persist to the end of the study. The present study did not show any improvements in BP or vascular function in overweight and obese individuals with psyllium fibre supplementation over 12 weeks of intervention. However, a healthy diet provided the greatest improvements in BP in overweight and obese subjects. Further research with hypertensive individuals is necessary to elucidate whether increased fibre consumption in the form of psyllium supplementation may provide a safe and acceptable means to reduce BP, vascular function and the risk of developing CVD.

Localised micro-mechanical stiffening in the ageing aorta

Age-related loss of tissue elasticity is a common cause of human morbidity and arteriosclerosis (vascular stiffening) is associated with the development of both fatal strokes and heart failure. However, in the absence of appropriate micro-mechanical testing methodologies, multiple structural remodelling events have been proposed as the cause of arteriosclerosis. Therefore, using a model of ageing in female sheep aorta (young: <18 months, old: >8 years) we: (i) quantified age-related macro-mechanical stiffness, (ii) localised in situ micro-metre scale changes in acoustic wave speed (a measure of tissue stiffness) and (iii) characterised collagen and elastic fibre remodelling. With age, there was an increase in both macro-mechanical stiffness and mean microscopic wave speed (and hence stiffness; young wave speed: 1701 ± 1 m s⁻¹, old wave speed: 1710 ± 1 m s⁻¹, p < 0.001) which was localized to collagen fibril-rich regions located between large elastic lamellae. These micro-mechanical changes were associated with increases in both collagen and elastic fibre content (collagen tissue area, young: 31 ± 2%, old: 40 ± 4%, p < 0.05; elastic fibre tissue area, young: 55 ± 3%, old: 69 ± 4%, p < 0.001). Localised collagen fibrosis may therefore play a key role in mediating age-related arteriosclerosis. Furthermore, high frequency scanning acoustic microscopy is capable of co-localising micro-mechanical and micro-structural changes in ageing tissues.

A constituent-based model of age-related changes in conduit arteries

In the present report, a constituent-based theoretical model of age-related changes in geometry and mechanical properties of conduit arteries is proposed. The model was based on the premise that given the time course of the load on an artery and the accumulation of advanced glycation end-products in the arterial tissue, the initial geometric dimensions and properties of the arterial tissue can be predicted by a solution of a boundary value problem for the governing equations that follow from finite elasticity, structure-based constitutive modeling within the constrained mixture theory, continuum damage theory, and global growth approach for stress-induced structure-based remodeling. An illustrative example of the age-related changes in geometry, structure, composition, and mechanical properties of a human thoracic aorta is considered. Model predictions were in good qualitative agreement with available experimental data in the literature. Limitations and perspectives for refining the model are discussed.

Differential Passive and Active Biaxial Mechanical Behaviors of Muscular and Elastic Arteries: Basilar Versus Common Carotid

Cerebrovascular disease continues to be responsible for significant morbidity and mortality. There is, therefore, a pressing need to understand better the biomechanics of both intracranial arteries and the extracranial arteries that feed these vessels. We used a validated four-fiber family constitutive relation to model passive biaxial stress-stretch behaviors of basilar and common carotid arteries and we developed a new relation to model their active biaxial responses. These data and constitutive relations allow the first full comparison of circumferential and axial biomechanical behaviors between a muscular (basilar) and an elastic (carotid) artery from the same species. Our active model describes the responses by both types of vessels to four doses of the vasoconstrictor endothelin-1 (10−10M, 10−9M, 10−8M, and 10−7M) and predicts levels of smooth muscle cell activation associated with basal tone under specific in vitro testing conditions. These results advance our understanding of the biomechanics of intracranial and extracranial arteries, which is needed to understand better their differential responses to similar perturbations in hemodynamic loading.

Arterial stiffness and dialysis calcium concentration

Arterial stiffness is the major determinant of isolated systolic hypertension and increased pulse pressure. Aortic stiffness is also associated with increased cardiovascular morbidity and mortality in patients with chronic kidney disease, hypertension, and general population. Hemodynamically, arterial stiffness results in earlier aortic pulse wave reflection leading to increased cardiac workload and decreased myocardial perfusion. Although the clinical consequence of aortic stiffness has been clearly established, its pathophysiology in various clinical conditions still remains poorly understood. The aim of the present paper is to review the studies that have looked at the impact of dialysis calcium concentration on arterial stiffness. Overall, the results of small short-term studies suggest that higher dialysis calcium is associated with a transient but significant increase in arterial stiffness. This calcium dependant increase in arterial stiffness is potentially explained by increased vascular smooth muscle tone of the conduit arteries and is not solely explained by changes in mean blood pressure. However, the optimal DCa remains to be determined, and long term studies are required to evaluate its impact on the progression of arterial stiffness.

Heart rate: a forgotten link in coronary artery disease?

A considerable body of evidence indicates that elevated resting heart rate is an independent, modifiable risk factor for cardiovascular events and mortality in patients with coronary artery disease. Elevated heart rate can produce adverse effects in several ways. Firstly, myocardial oxygen consumption is increased at high heart rates, but the time available for myocardial perfusion is reduced, increasing the likelihood of myocardial ischemia. Secondly, exposure of the large elastic arteries to cyclical stretch is increased at high heart rates. This effect can increase the rate at which components of the arterial wall deteriorate. Elastin fibers, which have an extremely slow rate of turnover in adult life, might be particularly vulnerable. Thirdly, elevated heart rate can predispose the myocardium to arrhythmias, and favor the development and progression of coronary atherosclerosis, by adversely affecting the balance between systolic and diastolic flow. Comparisons of the effects of the specific heart-rate-lowering drug ivabradine with those of β-blockers could help clarify the pathophysiological effects of elevated heart rate. Effective heart rate control among patients with coronary artery disease is uncommon in clinical practice, representing a missed therapeutic opportunity.

Automated measurement and statistical modelling of elastic laminae in arteries

Structural features of elastic laminae within arteries can provide vital information for both the mechanobiology and the biomechanics of the wall. In this paper, we propose, test and illustrate a new computer-based scheme for automated analysis of regional distributions of elastic laminae thickness, inter-lamellar distances and fragmentation furcation points (FPs) from standard histological images. Our scheme eliminates potential artefacts produced by tissue cutting, automatically aligns tissue according to physiologic orientations and performs cross-sectional measurements along radial directions. A statistical randomised complete block design and F test were used to assess the potential (non)-uniformity of lamellar thicknesses and separations along both radial and circumferential directions. Illustrative results for both normotensive and hypertensive thoracic porcine aorta revealed marked heterogeneity along the radial direction in nearly stress-free samples. Clearly, regional measurements can provide more detailed information about morphologic changes that cannot be gained by globally averaged evaluations alone. We also found that quantifying FP densities offers new information about potential elastin fragmentation, particularly in response to increased loading due to hypertension.

Matrix metalloproteinases: targets for doxycycline to prevent the vascular alterations of hypertension

Hypertension is associated with well known structural and functional alterations in both resistance and conduit arteries, which may be the result from long-lasting high blood pressure and may also be the cause of maintained hypertension and its complications. Therefore, in addition to lowering blood pressure, therapeutic strategies targeting the structural and functional modifications found in hypertensive patients may prevent the cardiovascular events and decrease the death rates associated with hypertension. Mounting evidence indicates that many vascular alterations associated with sustained hypertension are due to imbalanced matrix metalloproteinases (MMPs), a family of zinc-endopeptidases that degrade not only proteins of extracellular matrix (ECM) but several other substrates. Recent observations showed that abnormal MMP activity is a feature of the pathogenesis of hypertension and other diseases, thus justifying the development of drugs aiming at MMP downregulation. This review focuses on the extracellular actions of MMPs in hypertension-induced chronic vascular alterations. We then discuss the effects of MMP inhibitors, especially doxycycline, on the vascular changes associated with hypertension. There is now strong evidence that MMP inhibition with doxycycline (and maybe other MMP inhibitors) may attenuate the functional and structural alterations associated with hypertension, including increases in arterial stiffness. These beneficial effects may be, at least in part, independent of their antihypertensive effects.

A multi-layered computational model of coupled elastin degradation, vasoactive dysfunction, and collagenous stiffening in aortic aging

Arterial responses to diverse pathologies and insults likely occur via similar mechanisms. For example, many studies suggest that the natural process of aging and isolated systolic hypertension share many characteristics in arteries, including loss of functional elastin, decreased smooth muscle tone, and altered rates of deposition, and/or crosslinking of fibrillar collagen. Our aim is to show computationally how these coupled effects can impact evolving aortic geometry and mechanical behavior. Employing a thick-walled, multi-layered constrained mixture model, we suggest that a coupled loss of elastin and vasoactive function are fundamental mechanisms by which aortic aging occurs. Moreover, it is suggested that collagenous stiffening, although itself generally an undesirable process, can play a key role in attenuating excessive dilatation, perhaps including the enlargement of abdominal aortic aneurysms.

Large artery calcification on dialysis patients is located in the intima and related to atherosclerosis

BACKGROUND AND OBJECTIVES

Vascular calcification (VC) has a significant effect in cardiovascular diseases on dialysis patients. However, VC is assessed with x-ray-based techniques, which do not inform about calcium localization (intima, media, atherosclerosis-related). The aim of this work is to study VC and its related factors using arterial ultrasound to report the exact location of calcium.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was an observational, cross-sectional, case-control study that included 232 patients in dialysis and 208 age- and sex-matched controls with normal kidney function. Demographic data and laboratory values were collated. Carotid, femoral, and brachial ultrasounds were performed to assess VC and atherosclerosis burden using a standardized protocol.

RESULTS

Cardiovascular risk factors were predominantly found in controls, although the burden of atherosclerosis was higher in the dialysis group. VC was significantly more prevalent in the group of patients on dialysis than control subjects, and in both groups the most prevalent pattern of VC was linear calcification located in the intima of the artery wall. Age and undergoing dialysis (with or without previous cardiovascular diseases) were positively and significantly associated with linear calcification. Conversely, the absence of atherosclerosis and low levels of C-reactive protein and phosphorus significantly impeded the development of linear calcification.

CONCLUSIONS

VC in large, conduit arteries is more prevalent in patients on dialysis than controls and is predominantly located in a linear fashion in the intima of the arteries.

Acute effects of whey protein isolate on blood pressure, vascular function and inflammatory markers in overweight postmenopausal women

Previous evidence indicates that chronic consumption of dairy whey proteins has beneficial effects on CVD risk factors. The present study investigated the postprandial effects of whey protein isolate on blood pressure, vascular function and inflammatory markers in overweight and obese postmenopausal women. This was a randomised, three-way cross-over design study where twenty overweight and obese postmenopausal women consumed a breakfast meal in conjunction with one of three supplements: 45 g whey protein isolate, 45 g sodium caseinate or 45 g of a glucose control. Fasting and postprandial blood samples, blood pressure and pulse wave analysis readings were taken for up to 6 h. After consumption of the meal, both systolic and diastolic blood pressure, and augmentation index (AI) decreased initially for all interventions and gradually returned to baseline levels by 6 h. However, there were no significant differences in AI, systolic or diastolic blood pressure within or between the glucose control, casein or whey groups. There were also no significant group effects on plasma inflammatory markers (IL-6, TNF-α and C-reactive protein). The health effects previously seen with chronic whey protein ingestion were not seen in the acute 6 h postprandial period in relation to blood pressure, vascular function or inflammatory markers when compared with casein and a glucose control. This suggests that such effects are better observed from the long-term consumption of whey proteins.

Lifetime Fruit and Vegetable Consumption and Arterial Pulse Wave Velocity in Adulthood

Background—

The relationships between childhood lifestyle risk factors and adulthood pulse wave velocity (PWV) have not been reported. We studied whether childhood and adulthood lifestyle risk factors are associated with PWV assessed in adulthood.

Methods and Results—

The study cohort comprised 1622 subjects of the Cardiovascular Risk in Young Finns Study followed up for 27 years since baseline (1980; aged 3 to 18 years) with lifestyle risk factor data available since childhood. Arterial PWV was measured in 2007 by whole-body impedance cardiography device. Vegetable consumption in childhood was inversely associated with adulthood PWV (β=−0.06, P =0.02), and this association remained significant (β=−0.07, P =0.004) when adjusted for traditional risk factors (high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, systolic blood pressure, body mass index, and smoking). Vegetable consumption was also an independent predictor of PWV in adulthood when adjusted for lifestyle or traditional risk factors (β=−0.08, P =0.002 and β=−0.07, P =0.0007, respectively). Persistently high consumption of both fruits and vegetables from childhood to adulthood was associated with lower PWV compared with persistently low consumption ( P =0.03 for both). The number of lifestyle risk factors (the lowest quintile for vegetable consumption, fruit consumption, physical activity, and smoking) in childhood was directly associated with PWV in adulthood ( P =0.001). This association remained significant when adjusted for the number of lifestyle risk factors in adulthood ( P =0.003).

Conclusions—

These findings suggest that lifetime lifestyle risk factors, with low consumption of fruits and vegetables in particular, are related to arterial stiffness in young adulthood.

Structural modifications in the arterial wall during physiological aging and as a result of diabetes mellitus in a mouse model: are the changes comparable?

AIM

Vascular accelerated aging represents the major cause of morbidity and mortality in subjects with diabetes mellitus. In the present study, our aim was to compare premature functional and morphological changes in the arterial wall resulting from streptozotocin (STZ)-induced diabetes mellitus in mice over a short-term period with those that develop during physiological aging. The effect of aminoguanidine (AG) on the prevention of these alterations in the diabetic group was also analyzed.

METHODS

The vascular relaxation response to acetylcholine (ACh) in the mouse was tested in isolated segments of phenylephrine (Phe)-precontracted aorta at 2, 4 and 8 weeks (wk) of STZ-induced diabetes and compare to 12- and 84-wk-old mice. Aortic structural changes were investigated, and receptor for AGE (RAGE) aortic expression was quantified by western blot.

RESULTS

Compared to the 12-wk control group (76 ± 5%), significant endothelium-dependant relaxation (EDR) impairment was found in the group of 12-wk-old mice, which underwent a 4-wk diabetes-inducing STZ treatment (12wk-4WD) (52 ± 4%; P < 0.01) and was yet more apparent in the group of 16-wk-old mice, which underwent an 8-wk diabetes-inducing STZ treatment (16wk-8WD) (34 ± 4%; P < 0.001). The alteration in EDR was relatively comparable between the diabetic 12wk-4WD group and the 84-wk-old group (52.7 ± 4 vs. 48 ± 4%). Intima/media aortic thickening and aortic structural changes were significantly increased in the diabetic 12wk-4WD group and were even more apparent in the 84-wk group compared to the 12-wk controls. AG treatment in the 12wk-4WD+AG diabetic group significantly improved EDR, decreased RAGE expression and showed an aging preventive effect on the structural changes of the arterial wall.

CONCLUSION

Our study compared EDR linked to physiological aging with that observed in the case of STZ-induced diabetes over a short-term period, and demonstrated the beneficial effect of AG.

Modelling carotid artery adaptations to dynamic alterations in pressure and flow over the cardiac cycle

Motivated by recent clinical and laboratory findings of important effects of pulsatile pressure and flow on arterial adaptations, we employ and extend an established constrained mixture framework of growth (change in mass) and remodelling (change in structure) to include such dynamical effects. New descriptors of cell and tissue behavior (constitutive relations) are postulated and refined based on new experimental data from a transverse aortic arch banding model in the mouse that increases pulsatile pressure and flow in one carotid artery. In particular, it is shown that there was a need to refine constitutive relations for the active stress generated by smooth muscle, to include both stress- and stress rate-mediated control of the turnover of cells and matrix and to account for a cyclic stress-mediated loss of elastic fibre integrity and decrease in collagen stiffness in order to capture the reported evolution, over 8 weeks, of luminal radius, wall thickness, axial force and in vivo axial stretch of the hypertensive mouse carotid artery. We submit, therefore, that complex aspects of adaptation by elastic arteries can be predicted by constrained mixture models wherein individual constituents are produced or removed at individual rates and to individual extents depending on changes in both stress and stress rate from normal values.

Systemic arterial pressure at maturity in rats following chronic hypoxia in early life

BACKGROUND

The effect of prolonged hypoxemia in early life on systemic arterial blood pressure at maturity was assessed in Sprague-Dawley rats.

METHODS

Animals hypoxic in early life (12 males, 10 females) were raised in hypoxia (FiO₂ = 0.12) for the first 10 days of life and subsequently raised in normoxia, along with age-matched controls (11 males, 9 females). At 2 months of age, arterial blood pressure was recorded intravascularly using telemetry in awake and unrestrained animals over two 12-h night-time (active) and daytime (resting) periods. Aortic pulse wave velocity was assessed in six additional hypoxic pretreated and five control anesthetized 2-month-old male rats.

RESULTS

Systolic, mean, and pulse pressures were significantly greater in the hypoxic pretreated group compared to the control group during resting and active periods in both sexes (P ≤ 0.05). Diastolic pressure and heart rate did not differ between the two groups. Hypoxic pretreated males displayed significantly increased blood pressure variability during the resting period. Aortic pulse wave velocity was also found to be elevated in the hypoxic pretreated rats.

CONCLUSIONS

Prolonged hypoxic stress in early life in the rat is associated with increased systolic arterial pressure at maturity very likely due to decreased arterial compliance. These findings suggest that a nutrient-independent, postnatal stress may lead to long-lasting vascular alterations predisposing to increased arterial pressure at maturity. This raises the possibility that adult survivors of congenital cyanotic cardiac disease may be at risk for secondary cardiovascular morbidity unrelated to surgical repair or residual cardiac defects.

Effects of acetyl-L-carnitine and oxfenicine on aorta stiffness in diabetic rats

BACKGROUND

We compared the haemodynamic and metabolic effects of acetyl-L-carnitine (one of the carnitine derivatives) and of oxfenicine (a carnitine palmitoyltransferase-1 inhibitor) in streptozotocin-induced diabetes in male Wistar rats.

MATERIALS AND METHODS

Diabetes was induced by a single tail vein injection of 55mgkg(-1) streptozotocin. The diabetic animals daily treated with either acetyl-L-carnitine (150mgkg(-1) in drinking water) or oxfenicine (150mgkg(-1) by oral gavage) for 8weeks,were compared with the untreated age-matched diabetic controls. Arterial wave reflection was derived using the impulse response function of the filtered aortic input impedance spectra. Thiobarbituric acid reactive substances (TBARS) measurement was used to estimate malondialdehyde (MDA) content.

RESULTS

Oxfenicine, but not acetyl-L-carnitine, increased total peripheral resistance in diabetes, which paralleled its elevation in plasma levels of free fatty acids. By contrast, acetyl-L-carnitine, but not oxfenicine, resulted in a significant increase in wave transit time and a decrease in wave reflection factor, suggesting that acetyl-L-carnitine may attenuate the diabetes-induced deterioration in systolic loading condition for the left ventricle. This was in parallel with its lowering of MDA/TBARS content in plasma and aortic walls in diabetes. Acetyl-L-carnitine therapy also prevented the diabetes-related cardiac hypertrophy, as evidenced by the reduction in ratio of the left ventricular weight to body weight.

CONCLUSION

 Acetyl-L-carnitine, but not oxfenicine, attenuates aortic stiffening and cardiac hypertrophy, possibly through its decrease of lipid oxidation-derived MDA/TBARS in the rats with insulin deficiency.

Cardiovascular pathology in Hutchinson-Gilford progeria: correlation with the vascular pathology of aging

OBJECTIVE

Children with Hutchinson-Gilford progeria syndrome (HGPS) exhibit dramatically accelerated cardiovascular disease (CVD), causing death from myocardial infarction or stroke between the ages of 7 and 20 years. We undertook the first histological comparative evaluation between genetically confirmed HGPS and the CVD of aging.

METHODS AND RESULTS

We present structural and immunohistological analysis of cardiovascular tissues from 2 children with HGPS who died of myocardial infarction. Both had features classically associated with the atherosclerosis of aging, as well as arteriolosclerosis of small vessels. In addition, vessels exhibited prominent adventitial fibrosis, a previously undescribed feature of HGPS. Importantly, although progerin was detected at higher rates in the HGPS coronary arteries, it was also present in non-HGPS individuals. Between the ages of 1 month and 97 years, progerin staining increased an average of 3.34% per year (P<0.0001) in coronary arteries.

CONCLUSIONS

We find concordance among many aspects of cardiovascular pathology in both HGPS and geriatric patients. HGPS generates a more prominent adventitial fibrosis than typical CVD. Vascular progerin generation in young non-HGPS individuals, which significantly increases throughout life, strongly suggests that progerin has a role in cardiovascular aging of the general population.

Dynamic response of liquid-filled catheter systems for measurement of blood pressure: precision of measurements and reliability of the Pressure Recording Analytical Method with different disposable systems

PURPOSE

We aimed to compare the effects of a blood pressure transducer system specifically manufactured to limit underdamping artifacts with those of a standard system on hemodynamic parameter estimation and accuracy.

MATERIALS AND METHODS

Forty-three consecutive patients undergoing vascular surgery at the University of Florence, Italy, were included. Arterial blood pressure signal was simultaneously registered with 2 MostCare monitors, connected to the artery either by a standard transducer or a specific transducer manufactured to avoid underdamping artifacts (Resonance Over-Shoot Eliminator [R.O.S.E.]; Becton Dickinson, Becton Drive, NJ). Patients were divided into 2 groups: absence (C group) or presence (R group) of underdamping/resonance artifacts of blood pressure signal. Systolic blood pressure, cardiac index, maximal pressure/time ratio (dP/dt(MAX)), and cardiac cycle efficiency were recorded every 30 seconds for 30 minutes. A total of 2675 measurements were performed with 34.9% incidence of underdamping/resonance artifacts.

RESULTS

All hemodynamic parameters showed clinically acceptable differences in the C group; in contrast, the results differed greatly in the R group between standard and R.O.S.E. transducer (systolic blood pressure bias, 16.7 mm Hg; cardiac index bias, 0.24 L min(-1) m(-2); dP/dt(MAX) bias, 0.92 mm Hg/ms; cardiac cycle efficiency bias, 0.018 units).

CONCLUSIONS

Underdamping/resonance artifacts frequently affect blood pressure measurement in operating rooms and intensive care units and cause severe overestimation of systolic blood pressure and incorrect estimation of hemodynamic parameters when the pulse contour method is used.

Vascular aging: from molecular mechanism to clinical significance

The large and medium-sized arteries in elderly people show varying degrees of intimal and medial change. The medial change is known as age-related medial degeneration and sclerosis (ARMDS). The ARMDS results in systolic hypertension and left ventricular hypertrophy of the heart as a result of loss of arterial elasticity. It also causes aortic dilatation, or even aortic aneurysm. The ARMDS and atherosclerosis are distinct entities, but are often overlapped and confused with each other. The present review mainly focuses on ARMDS and briefly addresses atherosclerosis, and aging of arterioles, capillaries and veins. The smooth muscle cells in the inner half of the aortic media of elderly people degenerate and undergo apoptosis. This causes degradation of elastin fibers and the accumulation of collagen fibers in the media, but the inflammatory infiltrates are scarce. Biochemical studies showed an age-related decrease of elastin and its crosslinks, and an increase of collagen and its crosslink. Because the turnover of elastin is very long, it likely suffers from glycation (Maillard reaction) and glyco-oxidative reaction. The advanced glycation end-products accumulate in the aortic media with increasing age. Alcian-blue positive mucin accumulates in aortic media in elderly people. The major component of the increase of aortic mucin is chondroitin-6-sulfate. Microcalcification is frequent in the inner acellular portion of the aortic media in elderly people. Calcium contents increase with age. In conclusion, the ARMDS is a distinct pathological entity with clinical significance. The pathogenesis of ARMDS is unclear; the mechanical stress of elastin, endothelial dysfunction, and glycation of elastin are proposed.

Pathology of lethal peripartum broad ligament haematoma in 31 Thoroughbred mares

REASONS FOR PERFORMING STUDY

Broad ligament haemorrhage in peripartum mares is a life-threatening disease and there are few reports on the aetiology and pathogenesis of broad ligament haematoma.

OBJECTIVES

To obtain information regarding the sites for the early diagnosis and pathogenesis of broad ligament haematoma of mares.

METHODS

Thirty-one mares that died of broad ligament haematoma peripartum were examined pathologically for bleeding sites. The arterial distribution of 5 young mares with several parities served as negative controls.

RESULTS

Age and/or multiparity were the predisposing factors for the disease. Arterial injuries were most commonly observed in the uterine artery (24 of 31 mares). Among these, the proximal uterine artery that lies within 15 cm of the bifurcation of the iliac artery was the most frequent site for rupture (18 mares). The lesions occurred preferentially at the bifurcations, lateral part of curvatures and abrupt flexures of the artery. The morphology of the injuries was classified into 3 types: ruptures with and without longitudinal fissures, and transections. Histologically, the arterial wall adjacent to the rupture showed atrophy of smooth muscle cells with fibrosis of the tunica media and disruption and/or calcification of the internal elastic lamina.

CONCLUSIONS

Arterial injuries that led to broad ligament haematoma in peripartum mares occurred most frequently in the proximal uterine artery, and atrophy of smooth muscle cells with fibrosis of the arterial wall was as one of the predisposing factors in aged and multiparous mares.

POTENTIAL RELEVANCE

Monitoring small aneurysms, mural tearing, medial fibrosis at the proximal uterine artery by transrectal echography could provide useful information for the early diagnosis and possible prevention of broad ligament haematoma of peripartum mares.

Does accumulation of advanced glycation end products contribute to the aging phenotype?

BACKGROUND

Aging is a complex multifactorial process characterized by accumulation of deleterious changes in cells and tissues, progressive deterioration of structural integrity and physiological function across multiple organ systems, and increased risk of death.

METHODS

We conducted a review of the scientific literature on the relationship of advanced glycation end products (AGEs) with aging. AGEs are a heterogeneous group of bioactive molecules that are formed by the nonenzymatic glycation of proteins, lipids, and nucleic acids.

RESULTS

Humans are exposed to AGEs produced in the body, especially in individuals with abnormal glucose metabolism, and AGEs ingested in foods. AGEs cause widespread damage to tissues through upregulation of inflammation and cross-linking of collagen and other proteins. AGEs have been shown to adversely affect virtually all cells, tissues, and organ systems. Recent epidemiological studies demonstrate that elevated circulating AGEs are associated with increased risk of developing many chronic diseases that disproportionally affect older individuals.

CONCLUSIONS

Based on these data, we propose that accumulation of AGEs accelerate the multisystem functional decline that occurs with aging, and therefore contribute to the aging phenotype. Exposure to AGEs can be reduced by restriction of dietary intake of AGEs and drug treatment with AGE inhibitors and AGE breakers. Modification of intake and circulating levels of AGEs may be a possible strategy to promote health in old age, especially because most Western foods are processed at high temperature and are rich in AGEs.

Ultrasound measurement of peripheral endothelial dysfunction in type 2 diabetic patients: correlation with risk factors

The purpose of the study was to assess the endothelial dysfunction (ED) in type 2 diabetic patients ultrasonographically and estimate the correlation of ED with glycemia and other cardio-metabolic risk factors. 171 patient (age 60.0 + 8.5 years) with diagnosed type 2 diabetes and coronary artery disease (CAD) were randomly included in a cross sectional study. B-mode ultrasound system with a linear transducer of 7.5 MHz was used for evaluation of flow-mediated vasodilation in brachial artery (FMV). FMV was presented as a change of brachial artery diameter at rest and after limb ischemia, previously provoked by cuff inflation. Peripheral ED was found in 77.2% (132 patients). Multivariate logistic regression model defined: age (OR 1.071, 95% CI 1.003 1,143) and plasma cholesterol (OR 4.083 95% CI 1.080 17,017) as determinants for ED. Linear multivariate analysis presented duration of diabetes (Beta 0.173, Sig 0.024), and glycemia (Beta 0.132, Sig 0.044) to be associated independently with FMV value. Estimated factors influencing FMV, might be potential therapeutic targets for presented endothelial dysfunction in type 2 diabetic patients with coronary artery disease.

Plasma levels of advanced glycation end products are associated with haemolysis-related organ complications in sickle cell patients

Oxidative stress plays an important role in the pathophysiology of sickle cell disease (SCD). Plasma levels of advanced glycation end products (AGEs) are increased under oxidative conditions and are associated with disease severity in diabetes and inflammatory diseases. We investigated whether AGEs are increased in sickle cell patients and whether they are associated with SCD-related complications. Plasma levels of the AGEs pentosidine, N(ε) -(carboxymethyl)lysine (CML) and N(ε) -(carboxyethyl)lysine (CEL) were measured using single-column high performance liquid chromatography with fluorescence detection (pentosidine) and ultra performance liquid chromatography-tandem mass spectrometry (CML and CEL). Plasma levels of pentosidine and CML were increased in HbSS/HbSβ⁰-thalassaemia (n=60) and HbSC/HbSβ(+) -thalassaemia (n=42) patients during steady state as compared to healthy HbAA controls (n=30) without increments during painful crisis. CEL levels were comparable between all groups. Pentosidine and CML levels correlated significantly to haemolytic rate during the clinically asymptomatic state while pentosidine was significantly related to the number of haemolysis-related organ complications. The increased plasma AGE levels in sickle cell patients and their association with haemolysis and haemolysis-related complications suggest AGEs might be implicated in the pathophysiology of the haemolytic phenotype of SCD. Measurement of AGEs might be useful in predicting organ complications in SCD.

On constitutive descriptors of the biaxial mechanical behaviour of human abdominal aorta and aneurysms

The abdominal aorta (AA) in older individuals can develop an aneurysm, which is of increasing concern in our ageing population. The structural integrity of the ageing aortic wall, and hence aneurysm, depends primarily on effective elastin and multiple families of oriented collagen fibres. In this paper, we show that a structurally motivated phenomenological 'four-fibre family' constitutive relation captures the biaxial mechanical behaviour of both the human AA, from ages less than 30 to over 60, and abdominal aortic aneurysms. Moreover, combining the statistical technique known as non-parametric bootstrap with a modal clustering method provides improved confidence intervals for estimated best-fit values of the eight associated constitutive parameters. It is suggested that this constitutive relation captures the well-known loss of structural integrity of elastic fibres owing to ageing and the development of abdominal aneurysms, and that it provides important insight needed to construct growth and remodelling models for aneurysms, which in turn promise to improve our ability to predict disease progression.

Changes in aortic stiffness related to elastic fiber network anomalies in the Brown Norway rat during maturation and aging

Adult Brown Norway (BN) rats exhibit numerous internal elastic lamina (IEL) ruptures in the abdominal aorta (AA) and a lower aortic elastin-to-collagen ratio (E/C) compared with other strains. We studied here AA mechanical properties in BN compared with control strains. AA stiffness (assessed by plotting elastic modulus/wall-stress curves obtained under anesthesia), thoracic aorta elastin and collagen contents, and IEL ruptures in AA were measured in male BN and LOU rats aged 6, 10, and 15 wk. The Long Evans (LE) control strain was compared with BN at more advanced ages (15, 28, and 64 wk). At all ages, aortic E/C was lower in BN than in control strains. At 6 wk, AA stiffness was greater in BN than in LOU. In both strains, AA stiffness decreased between 6 and 10 wk, more so in BN than in LOU, and then increased, reaching similar values at 15 wk. BN AA stiffness was not different from that of LE at 15 and 28 wk, but was significantly lower at 64 wk. The increased stiffness in young BN rat AA may be due to the decreased E/C. IEL rupture onset in the BN around 7–8 wk, which decreases stiffness, as suggested by its pharmacological modulation, abolished such differences by 15 wk. Thereafter, age-related AA stiffness increased less in BN than in LE, likely due to the numerous IEL ruptures. We conclude that, in the BN rat, the lower E/C and the presence of IEL ruptures have opposing effects on arterial stiffness.

The chronic effects of whey proteins on blood pressure, vascular function, and inflammatory markers in overweight individuals

Limited evidence suggests that dairy whey protein may be the major dairy component that is responsible for health benefits currently associated with increased dairy consumption. Whey proteins may reduce blood pressure and improve cardiovascular health. This study evaluated the effects of whey protein supplementation on blood pressure, vascular function and inflammatory markers compared to casein and glucose (control) supplementation in overweight/obese individuals. The subjects were randomized to either whey protein, casein or glucose supplementation for 12 weeks according to a parallel design. In all, 70 men and women with a mean (+/-s.e.m.) BMI (kg/m(2)) of 31.3 +/- 0.8 completed the study. Systolic blood pressure (SBP) decreased significantly at week 6 compared to baseline in the whey and casein groups, (P = 0.028 and P = 0.020, respectively) and at week 12 (P = 0.020, and P = 0.017, respectively). Diastolic blood pressure (DBP) decreased significantly compared to baseline in the whey and casein groups (P = 0.038 and P = 0.042, respectively) at week 12. DBP decreased significantly in the whey and casein groups (P = 0.025, P = 0.038, respectively) at week 12 compared to the control group. Augmentation index (AI) was significantly lower from baseline at 12 weeks (P = 0.021) in the whey group. AI decreased significantly in the whey group at 12 weeks compared to control (P = 0.006) and casein (P = 0.006). There were no significant changes in inflammatory markers within or between groups. This study demonstrated that supplementation with whey protein improves blood pressure and vascular function in overweight and obese individuals.

An analysis of prospective risk factors for aortic stiffness in men: 20-year follow-up from the Caerphilly prospective study

Arterial stiffness is an important determinant of cardiovascular risk. The precise risk factors for arterial stiffening remain unclear. We aimed to identify potential risk factors using prospective exposure data from the Caerphilly Prospective Study. Aortic pulse wave velocity and augmentation index were measured in 825 men and related to current (2004) and baseline (1979-1988) anthropometric, hemodynamic, and biochemical factors. The mean age of the men was 74 years, with an average follow-up of 20 years. The only independent baseline predictors of current velocity were pulse pressure (standardized beta-coefficient: 0.58), C-reactive protein (0.35), glucose (0.25), and waist circumference (0.23). The sole baseline predictor of current augmentation index was fibrinogen (0.78). After additional adjustment for the corresponding current risk factor, pulse wave velocity was best related to cumulative exposure to C-reactive protein, whereas augmentation index was most strongly related to current levels. Velocity was also more strongly correlated with baseline levels of triglycerides and smoking but with current waist circumference. The pulse pressure heart rate product assessed over the whole of 20 years was independently correlated with aortic pulse wave velocity but not augmentation index. Other than blood pressure, established cardiovascular risk factors have only a modest effect on aortic stiffness and wave reflection. Inflammation and the level of repetitive cyclic stress are important predictors of aortic stiffness, whereas wave reflection is predicted by acute inflammation only. Adequate control of pulse pressure and heart rate, as well as reducing inflammation, may, in the long-term, retard aortic stiffening, although this remains to be tested directly.

Critical appraisal of the differential effects of antihypertensive agents on arterial stiffness

Increased central arterial stiffness, involving accelerated vascular ageing of the aorta, is a powerful and independent risk factor for early mortality and provides prognostic information above and beyond traditional risk factors for cardiovascular disease (CVD). Central arterial stiffness is an important determinant of pulse pressure; therefore, any pathological increase may result in left ventricular hypertrophy and impaired coronary perfusion. Central artery stiffness can be assessed noninvasively by measurement of aortic pulse wave velocity, which is the gold standard for measurement of arterial stiffness. Earlier, it was believed that changes in arterial stiffness, which are primarily influenced by long-term pressure-dependent structural changes, may be slowed but not reversed by pharmacotherapy. Recent studies with drugs that inhibit the renin-angiotensin-aldosterone system, advanced glycation end products crosslink breakers, and endothelin antagonists suggest that blood pressure (BP)-independent reduction and reversal of arterial stiffness are feasible. We review the recent literature on the differential effect of antihypertensive agents either as monotherapy or combination therapy on arterial stiffness. Arterial stiffness is an emerging therapeutic target for CVD risk reduction; however, further clinical trials are required to confirm whether BP-independent changes in arterial stiffness directly translate to a reduction in CVD events.

Decreased S-nitrosylation of tissue transglutaminase contributes to age-related increases in vascular stiffness

RATIONALE

Although an age-related decrease in NO bioavailability contributes to vascular stiffness, the underlying molecular mechanisms remain incompletely understood. We hypothesize that NO constrains the activity of the matrix crosslinking enzyme tissue transglutaminase (TG2) via S-nitrosylation in young vessels, a process that is reversed in aging.

OBJECTIVE

We sought to determine whether endothelium-dependent NO regulates TG2 activity by S-nitrosylation and whether this contributes to age-related vascular stiffness.

METHODS AND RESULTS

We first demonstrate that NO suppresses activity and increases S-nitrosylation of TG2 in cellular models. Next, we show that nitric oxide synthase (NOS) inhibition leads to increased surface and extracellular matrix-associated TG2. We then demonstrate that endothelium-derived bioactive NO primarily mediates its effects through TG2, using TG2(-/-) mice chronically treated with the NOS inhibitor l-N(G)-nitroarginine methyl ester (L-NAME). We confirm that TG2 activity is modulated by endothelium-derived bioactive NO in young rat aorta. In aging rat aorta, although TG2 expression remains unaltered, its activity increases and S-nitrosylation decreases. Furthermore, TG2 inhibition decreases vascular stiffness in aging rats. Finally, TG2 activity and matrix crosslinks are augmented with age in human aorta, whereas abundance remains unchanged.

CONCLUSIONS

Decreased S-nitrosylation of TG2 and increased TG activity lead to enhanced matrix crosslinking and contribute to vascular stiffening in aging. TG2 appears to be the member of the transglutaminase family primarily contributing to this phenotype. Inhibition of TG2 could thus represent a therapeutic target for age-associated vascular stiffness and isolated systolic hypertension.

Theoretical study on the effects of pressure-induced remodeling on geometry and mechanical non-homogeneity of conduit arteries

A structure-based mathematical model for the remodeling of arteries in response to sustained hypertension is proposed. The model is based on the concepts of volumetric growth and constitutive modeling of the arterial tissue within the framework of the constrained mixture theory. The major novel result of this study is that remodeling is associated with a local change in the mass fractions of the wall constituents that ultimately leads to mechanical non-homogeneity of the arterial wall. In the new homeostatic state that develops after a sustained increase in arterial pressure, the mass fraction of elastin decreases from the intimal side to the adventitial side of arteries, while the collagen fraction manifests an opposite trend. The results obtained are supported by some experimental observations reported in the literature.

Blood flow interplays with elastin: collagen and MMP: TIMP ratios to maintain healthy vascular structure and function

Differential vascular remodeling is one of the major mechanisms of heterogeneity in atherosclerosis. The structural and functional heterogeneity between arteries and veins determines the degree of vascular remodeling. Matrix metalloproteases (MMPs) and their tissue inhibitors (TIMPs) play key roles in vascular structural and functional remodeling. We hypothesized that the level of blood flow in different arteries and veins caused structural and functional heterogeneity that ultimately determined potential vascular remodeling. To test this hypothesis, in vivo blood flow and blood pressure in the aorta, carotid, femoral artery, and femoral vein was measured in male Sprague-Dawley rats (weight 380–400 gm). Arterial and venous pressures were measured by PE-50 catheter cannulation. Blood flow was measured by a transonic ultrasound system. The aortic arch, femoral and carotid arteries, and abdominal vena cava were isolated to determine the expression of MMP-2, -9, -12, and -13 and TIMP-1, -3, and -4 by Western blot and in gelatin gel zymography. Masson trichrome and van Gieson stains were used to stain the histologic tissue sections. The results revealed that blood flow was higher in the aorta and carotid artery than the femoral artery and vein. MMP-9 and MMP-13 were higher in the carotid artery in comparison with the other blood vessels, while TIMP-3 showed higher expression in the aorta than the arteries. Further, the MMP-9 activity was significantly higher in the carotid artery than in the aorta and femoral artery. There was a higher degree of basement membrane collagen in the femoral artery and therefore a low elastin: collagen ratio, while in the carotid artery a higher level of elastin and, therefore, a high elastin: collagen ratio was found. The results suggested that medial thickness and elastin:collagen ratios had a threshold in blood flow in the range 0.6–2.5 mL/min, which increased robustly if blood flow increased to 2.7 mL/min. This pattern was inverted by the total MMP:TIMP ratio. We conclude that vascular remodeling is a function of rate of blood flow, which would in turn be determined by the amounts of MMPs and their inhibitors present. The study combined the endothelial and dynamic (blood flow/pressure) components that affect medial thickness and elastin: collagen ratios.