Role of the extracellular matrix in age-related modifications of the rat aorta. Ultrastructural, morphometric, and enzymatic evaluations

Vascular Stiffness in Aging and Disease

The goal of this review is to provide further understanding of increased vascular stiffness with aging, and how it contributes to the adverse effects of major human diseases. Differences in stiffness down the aortic tree are discussed, a topic requiring further research, because most prior work only examined one location in the aorta. It is also important to understand the divergent effects of increased aortic stiffness between males and females, principally due to the protective role of female sex hormones prior to menopause. Another goal is to review human and non-human primate data and contrast them with data in rodents. This is particularly important for understanding sex differences in vascular stiffness with aging as well as the changes in vascular stiffness before and after menopause in females, as this is controversial. This area of research necessitates studies in humans and non-human primates, since rodents do not go through menopause. The most important mechanism studied as a cause of age-related increases in vascular stiffness is an alteration in the vascular extracellular matrix resulting from an increase in collagen and decrease in elastin. However, there are other mechanisms mediating increased vascular stiffness, such as collagen and elastin disarray, calcium deposition, endothelial dysfunction, and the number of vascular smooth muscle cells (VSMCs). Populations with increased longevity, who live in areas called “Blue Zones,” are also discussed as they provide additional insights into mechanisms that protect against age-related increases in vascular stiffness. Such increases in vascular stiffness are important in mediating the adverse effects of major cardiovascular diseases, including atherosclerosis, hypertension and diabetes, but require further research into their mechanisms and treatment.

Impact of acute dynamic exercise on vascular stiffness in the retinal arteriole in healthy subjects

Acute exercise can improve vascular stiffness in the conduit artery, but its effect on the retinal arterioles is unknown. The present study investigated the effects of acute dynamic exercise on retinal vascular stiffness. In experiment 1, we measured the cardio-ankle vascular index (CAVI), carotid artery intima-media thickness (carotid IMT), and retinal blood velocity by laser speckle flowgraphy in 28 healthy old and 28 young men (69 ± 3 and 23 ± 3 years, respectively). Pulse waveform variables, which were used as an index of retinal vascular stiffness, were assessed by retinal blood flow velocity profile analysis. In experiment 2, 18 healthy old and 18 young men (69 ± 3 and 23 ± 3 years, respectively) underwent assessment of pulse waveform variables after a 30-min bout of moderate cycling exercise at an intensity of 60% heart rate reserve. There was a significant difference in the baseline pulse waveform variables between the old and young groups. Pulse waveform variables in the retinal arteriole did not significantly change after acute dynamic exercise, whereas CAVI significantly decreased. These findings suggest that retinal vascular stiffness does not change by acute exercise. The effect of exercise on vascular stiffness in the retinal arterioles might be different from that in the conduit artery.

Dynamic Crosstalk between Vascular Smooth Muscle Cells and the Aged Extracellular Matrix

Vascular aging is accompanied by the fragmentation of elastic fibers and collagen deposition, leading to reduced distensibility and increased vascular stiffness. A rigid artery facilitates elastin to degradation by MMPs, exposing vascular cells to greater mechanical stress and triggering signaling mechanisms that only exacerbate aging, creating a self-sustaining inflammatory environment that also promotes vascular calcification. In this review, we highlight the role of crosstalk between smooth muscle cells and the vascular extracellular matrix (ECM) and how aging promotes smooth muscle cell phenotypes that ultimately lead to mechanical impairment of aging arteries. Understanding the underlying mechanisms and the role of associated changes in ECM during aging may contribute to new approaches to prevent or delay arterial aging and the onset of cardiovascular diseases.

Investigation of Pathophysiological Aspects of Aortic Growth, Remodeling, and Failure Using a Discrete-Fiber Microstructural Model

Aortic aneurysms are inherently unpredictable. One can never be sure whether any given aneurysm may rupture or dissect. Clinically, the criteria for surgical intervention are based on size and growth rate, but it remains difficult to identify a high-risk aneurysm, which may require intervention before the cutoff criteria, versus an aneurysm than can be treated safely by more conservative measures. In this work, we created a computational microstructural model of a medial lamellar unit (MLU) incorporating (1) growth and remodeling laws applied directly to discrete, individual fibers, (2) separate but interacting fiber networks for collagen, elastin, and smooth muscle, (3) active and passive smooth-muscle cell mechanics, and (4) failure mechanics for all three fiber types. The MLU model was then used to study different pathologies and microstructural anomalies that may play a role in vascular growth and failure. Our model recapitulated many aspects of arterial remodeling under hypertension with no underlying genetic syndrome including remodeling dynamics, tissue mechanics, and failure. Syndromic effects (smooth muscle cell (SMC) dysfunction or elastin fragmentation) drastically changed the simulated remodeling process, tissue behavior, and tissue strength. Different underlying pathologies were able to produce similarly dilatated vessels with different failure properties, providing a partial explanation for the imperfect nature of aneurysm size as a predictor of outcome.

Elastin-Based Materials: Promising Candidates for Cardiac Tissue Regeneration

Stroke and cardiovascular episodes are still some of the most common diseases worldwide, causing millions of deaths and costing billions of Euros to healthcare systems. The use of new biomaterials with enhanced biological and physical properties has opened the door to new approaches in cardiovascular applications. Elastin-based materials are biomaterials with some of the most promising properties. Indeed, these biomaterials have started to yield good results in cardiovascular and angiogenesis applications. In this review, we explore the latest trends in elastin-derived materials for cardiac regeneration and the different possibilities that are being explored by researchers to regenerate an infarcted muscle and restore its normal function. Elastin-based materials can be processed in different manners to create injectable systems or hydrogel scaffolds that can be applied by simple injection or as patches to cover the damaged area and regenerate it. Such materials have been applied to directly regenerate the damaged cardiac muscle and to create complex structures, such as heart valves or new bio-stents that could help to restore the normal function of the heart or to minimize damage after a stroke. We will discuss the possibilities that elastin-based materials offer in cardiac tissue engineering, either alone or in combination with other biomaterials, in order to illustrate the wide range of options that are being explored. Moreover, although tremendous advances have been achieved with such elastin-based materials, there is still room for new approaches that could trigger advances in cardiac tissue regeneration.

Temporal changes in peritoneal cell phenotype and neoelastic matrix induction with hyaluronan oligomers and TGF-β1 after implantation of engineered conduits

The neoassembly and maturation of elastic matrix is an important challenge for engineering small-diameter grafts for patients with peripheral artery disease. We have previously shown that hyaluronan oligomers and transforming growth factor-β (elastogenic factors or EFs) promote elastogenesis in smooth muscle cell (SMC) culture. However, their combined effects on macrophages and inflammatory cells in vivo are unknown. This information is needed to use the body (e.g., peritoneal cavity) as an "in vivo bioreactor" to recruit autologous cells to implanted EF-functionalized scaffolds. In this study, we determined if peritoneal fluid cells respond to EFs like smooth muscle cells and if these responses differ between cells sourced during different stages of inflammation triggered by scaffold implantation. Electrospun poly(ε-caprolactone)/collagen conduits were implanted in the peritoneal cavity prior to peritoneal fluid collection at 3-42 days postimplantation. Cells from the fluid were cultured in vitro with and without EFs to determine their response. Their phenotype/behaviour was assessed with a DNA assay, quantitative real-time PCR, and immunofluorescence. The EFs reduced peritoneal cell proliferation, maintained cell contractility, and unexpectedly did not exhibit proelastic effects, which we attributed to differences in cell density. We found the greatest elastin deposition in regions containing a high cell density. Further, we found that cells isolated from the peritoneal cavity at longer times after conduit implantation responded better to the EFs and exhibited more CD31 expression than cells at an earlier time point. Overall, this study provides information about the potential use of EFs in vivo and can guide the design of future tissue-engineered vascular grafts.

Synergistic effect of low K and D vitamin status on arterial stiffness in a general population

Both vitamins K and D are nutrients with pleiotropic functions in human tissues. The metabolic role of these vitamins overlaps considerably in calcium homeostasis. We analyzed their potential synergetic effect on arterial stiffness. In a cross-sectional study, we analyzed aortic pulse wave velocity (aPWV) in 1023 subjects from the Czech post-MONICA study. Desphospho-uncarboxylated matrix γ-carboxyglutamate protein (dp-ucMGP), a biomarker of vitamin K status, was measured by sandwich ELISA and 25-hydroxyvitamin D3 (25-OH-D3) by a commercial immunochemical assay. In a subsample of 431 subjects without chronic disease or pharmacotherapy, we detected rs2228570 polymorphism for the vitamin D receptor. After adjustment for confounders, aPWV was independently associated with both factors: dp-ucMGP [β-coefficient(S.E.M.)=13.91(4.87); P=.004] and 25-OH-D3 [0.624(0.28); P=.027]. In a further analysis, we divided subjects according to dp-ucMGP and 25-OH-D3 quartiles, resulting in 16 subgroups. The highest aPWV had subjects in the top quartile of dp-ucMGP plus bottom quartile of 25-OH-D3 (i.e., in those with insufficient status of both vitamin K and vitamin D), while the lowest aPVW had subjects in the bottom quartile of dp-ucMGP plus top quartile of 25-OH-D3 [9.8 (SD2.6) versus 6.6 (SD1.6) m/s; P<.0001]. When we compared these extreme groups of vitamin K and D status, the adjusted odds ratio for aPWV≥9.3 m/s was 6.83 (95% CI:1.95-20.9). The aPWV was also significantly higher among subjects bearing the GG genotype of rs2228570, but only in those with a concomitantly poor vitamin K status. In conclusion, we confirmed substantial interaction of insufficient K and D vitamin status in terms of increased aortic stiffness.

Desphospho-uncarboxylated matrix Gla protein is associated with increased aortic stiffness in a general population

Matrix Gla protein (MGP), a natural inhibitor of calcification, strongly correlates with the extent of coronary calcification. Vitamin K is the essential cofactor for the activation of MGP. The nonphosphorylated-uncarboxylated isoform of MGP (dp-ucMGP) reflects the status of this vitamin. We investigated whether there is an association between dp-ucMGP and stiffness of elastic and muscular-type large arteries in a random sample from the general population. In a cross-sectional design, we analyzed 1087 subjects from the Czech post-MONICA study. Aortic and femoro-popliteal pulse wave velocities (PWVs) were measured using a Sphygmocor device. Dp-ucMGP concentrations were assessed in freshly frozen samples by enzyme-linked immunosorbent assay methods using the InaKtif MGP iSYS pre-commercial kit developed by IDS and VitaK. Aortic PWV significantly (P<0.0001) increased across the dp-ucMGP quartiles. After adjustment for all potential confounders, aortic PWV independently correlated with dp-ucMGP (with beta coefficient (s.d.) 11.61 (5.38) and P-value=0.031). In a categorized manner, subjects in the top quartile of dp-ucMGP (⩾ 671 pmol l(-1)) had a higher risk of elevated aortic PWV, with corresponding adjusted odds ratio (95% confidence interval) 1.73 (1.17-2.5). In contrast, no relation between dp-ucMGP and femoro-popliteal PWV was found. In conclusion, increased dp-ucMGP, which is a circulating biomarker of vitamin K status and vascular calcification, is independently associated with aortic stiffness, but not with stiffness of distal muscular-type arteries.

Serum carboxy-terminal telopeptide of type I collagen levels are associated with carotid atherosclerosis in patients with cardiovascular risk factors

Carboxy-terminal telopeptide of type I collagen (ICTP) is generated through matrix metalloproteinase (MMP)-dependent type I collagen digestion, and has been widely utilized as a biomarker for bone turnover. The fact that atherosclerotic lesions are rich in both type I collagen and MMP-producing macrophages led to the hypothesis that serum ICTP concentrations may serve as a non-invasive clinical biomarker for atherosclerosis. Therefore, the association of serum ICTP concentrations with the maximum intima-media thickness (IMT) of carotid arteries, a surrogate index of systemic atherosclerosis, or brachial-ankle pulse wave velocity (baPWV) in patients with atherosclerotic risk factors was evaluated. A total of 52 male and 65 female (mean age: 62.8 yrs) patients without renal failure, malignancies or bone diseases known to affect serum ICTP concentrations were recruited. Patients with max IMTs ≥1.1 mm showed significantly higher serum ICTP concentrations compared with patients with max IMTs <1.1 mm (3.33 ± 0.97 vs 2.82 ± 0.65 ng/mL, p<0.05). Serum ICTP concentration was also positively correlated with max IMT (p<0.001) or baPWV values (p<0.05). Multivariate analyses also revealed that serum ICTP concentrations were correlated with max IMT (p<0.001; 95% CI 0.200 to 0.454). These results suggest that serum ICTP concentrations can be used as a non-invasive biomarker for systemic atherosclerosis.

Circulating desmosine levels do not predict emphysema progression but are associated with cardiovascular risk and mortality in COPD

Elastin degradation is a key feature of emphysema and may have a role in the pathogenesis of atherosclerosis associated with chronic obstructive pulmonary disease (COPD). Circulating desmosine is a specific biomarker of elastin degradation. We investigated the association between plasma desmosine (pDES) and emphysema severity/progression, coronary artery calcium score (CACS) and mortality.pDES was measured in 1177 COPD patients and 110 healthy control subjects from two independent cohorts. Emphysema was assessed on chest computed tomography scans. Aortic arterial stiffness was measured as the aortic-femoral pulse wave velocity.pDES was elevated in patients with cardiovascular disease (p<0.005) and correlated with age (rho=0.39, p<0.0005), CACS (rho=0.19, p<0.0005) modified Medical Research Council dyspnoea score (rho=0.15, p<0.0005), 6-min walking distance (rho=-0.17, p<0.0005) and body mass index, airflow obstruction, dyspnoea, exercise capacity index (rho=0.10, p<0.01), but not with emphysema, emphysema progression or forced expiratory volume in 1 s decline. pDES predicted all-cause mortality independently of several confounding factors (p<0.005). In an independent cohort of 186 patients with COPD and 110 control subjects, pDES levels were higher in COPD patients with cardiovascular disease and correlated with arterial stiffness (p<0.05).In COPD, excess elastin degradation relates to cardiovascular comorbidities, atherosclerosis, arterial stiffness, systemic inflammation and mortality, but not to emphysema or emphysema progression. pDES is a good biomarker of cardiovascular risk and mortality in COPD.

Extracellular Matrix Disarray as a Mechanism for Greater Abdominal Versus Thoracic Aortic Stiffness With Aging in Primates

OBJECTIVE

Increased vascular stiffness is central to the pathophysiology of aging, hypertension, diabetes mellitus, and atherosclerosis. However, relatively few studies have examined vascular stiffness in both the thoracic and the abdominal aorta with aging, despite major differences in anatomy, embryological origin, and relation to aortic aneurysm.

APPROACH AND RESULTS

The 2 other unique features of this study were (1) to study young (9±1 years) and old (26±1 years) male monkeys and (2) to study direct and continuous measurements of aortic pressure and thoracic and abdominal aortic diameters in conscious monkeys. As expected, aortic stiffness, β, was increased P<0.05, 2- to 3-fold, in old versus young thoracic aorta and augmented further with superimposition of acute hypertension with phenylephrine. Surprisingly, stiffness was not greater in old thoracic aorta than in young abdominal aorta. These results can be explained, in part, by the collagen/elastin ratio, but more importantly, by disarray of collagen and elastin, which correlated best with vascular stiffness. However, vascular smooth muscle cell stiffness was not different in thoracic versus abdominal aorta in either young or old monkeys.

CONCLUSIONS

Thus, aortic stiffness increases with aging as expected, but the most severe increases in aortic stiffness observed in the abdominal aorta is novel, where values in young monkeys equaled, or even exceeded, values of thoracic aortic stiffness in old monkeys. These results can be explained by alterations in collagen/elastin ratio, but even more importantly by collagen and elastin disarray.

Aging is associated with changes to the biomechanical properties of the posterior cerebral artery and parenchymal arterioles

Artery remodeling, described as a change in artery structure, may be responsible for the increased risk of cardiovascular disease with aging. Although the risk for stroke is known to increase with age, relatively young animals have been used in most stroke studies. Therefore, more information is needed on how aging alters the biomechanical properties of cerebral arteries. Posterior cerebral arteries (PCAs) and parenchymal arterioles (PAs) are important in controlling brain perfusion. We hypothesized that aged (22-24 mo old) C57bl/6 mice would have stiffer PCAs and PAs than young (3-5 mo old) mice. The biomechanical properties of the PCAs and PAs were assessed by pressure myography. Data are presented as means ± SE of young vs. old. In the PCA, older mice had increased outer (155.6 ± 3.2 vs. 169.9 ± 3.2 μm) and lumen (116.4 ± 3.6 vs. 137.1 ± 4.7 μm) diameters. Wall stress (375.6 ± 35.4 vs. 504.7 ± 60.0 dyn/cm(2)) and artery stiffness (β-coefficient: 5.2 ± 0.3 vs. 7.6 ± 0.9) were also increased. However, wall strain (0.8 ± 0.1 vs. 0.6 ± 0.1) was reduced with age. In the PAs from old mice, wall thickness (3.9 ± 0.3 vs. 5.1 ± 0.2 μm) and area (591.1 ± 95.4 vs. 852.8 ± 100 μm(2)) were increased while stress (758.1 ± 100.0 vs. 587.2 ± 35.1 dyn/cm(2)) was reduced. Aging also increased mean arterial and pulse pressures. We conclude that age-associated remodeling occurs in large cerebral arteries and arterioles and may increase the risk of cerebrovascular disease.

Nitric oxide stimulates matrix synthesis and deposition by adult human aortic smooth muscle cells within three-dimensional cocultures

Vascular diseases are characterized by the over-proliferation and migration of aortic smooth muscle cells (SMCs), and degradation of extracellular matrix (ECM) within the vessel wall, leading to compromise in cell-cell and cell-matrix signaling pathways. Tissue engineering approaches to regulate SMC over-proliferation and enhance healthy ECM synthesis showed promise, but resulted in low crosslinking efficiency. Here, we report the benefits of exogenous nitric oxide (NO) cues, delivered from S-Nitrosoglutathione (GSNO), to cell proliferation and matrix deposition by adult human aortic SMCs (HA-SMCs) within three-dimensional (3D) biomimetic cocultures. A coculture platform with two adjacent, permeable 3D culture chambers was developed to enable paracrine signaling between vascular cells. HA-SMCs were cultured in these chambers within collagen hydrogels, either alone or in the presence of human aortic endothelial cells (HA-ECs) cocultures, and exogenously supplemented with varying GSNO dosages (0-100 nM) for 21 days. Results showed that EC cocultures stimulated SMC proliferation within GSNO-free cultures. With increasing GSNO concentration, HA-SMC proliferation decreased in the presence or absence of EC cocultures, while HA-EC proliferation increased. GSNO (100 nM) significantly enhanced the protein amounts synthesized by HA-SMCs, in the presence or absence of EC cocultures, while lower dosages (1-10 nM) offered marginal benefits. Multi-fold increases in the synthesis and deposition of elastin, glycosaminoglycans, hyaluronic acid, and lysyl oxidase crosslinking enzyme (LOX) were noted at higher GSNO dosages, and coculturing with ECs significantly furthered these trends. Similar increases in TIMP-1 and MMP-9 levels were noted within cocultures with increasing GSNO dosages. Such increases in matrix synthesis correlated with NO-stimulated increases in endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) expression within EC and SMC cultures, respectively. Results attest to the benefits of delivering NO cues to suppress SMC proliferation and promote robust ECM synthesis and deposition by adult human SMCs, with significant applications in tissue engineering, biomaterial scaffold development, and drug delivery.

Ageing and microvasculature

A decline in the function of the microvasculature occurs with ageing. An impairment of endothelial properties represents a main aspect of age-related microvascular alterations. Endothelial dysfunction manifests itself through a reduced angiogenic capacity, an aberrant expression of adhesion molecules and an impaired vasodilatory function. Increased expression of adhesion molecules amplifies the interaction with circulating factors and inflammatory cells. The latter occurs in both conduit arteries and resistance arterioles. Age-related impaired function also associates with phenotypic alterations of microvascular cells, such as endothelial cells, smooth muscle cells and pericytes. Age-related morphological changes are in most of cases organ-specific and include microvascular wall thickening and collagen deposition that affect the basement membrane, with the consequent perivascular fibrosis. Data from experimental models indicate that decreased nitric oxide (NO) bioavailability, caused by impaired eNOS activity and NO inactivation, is one of the causes responsible for age-related microvascular endothelial dysfunction. Consequently, vasodilatory responses decline with age in coronary, skeletal, cerebral and vascular beds. Several therapeutic attempts have been suggested to improve microvascular function in age-related end-organ failure, and include the classic anti-atherosclerotic and anti-ischemic treatments, and also new innovative strategies. Change of life style, antioxidant regimens and anti-inflammatory treatments gave the most promising results. Research efforts should persist to fully elucidate the biomolecular basis of age-related microvascular dysfunction in order to better support new therapeutic strategies aimed to improve quality of life and to reduce morbidity and mortality among the elderly patients.

Profilin-1 promotes the development of hypertension-induced artery remodeling

Hypertension is associated with the structural remodeling and stiffening of arteries and is known to increase cardiovascular risk. In the present study, we investigated the effects of overexpression and knock down of profilin-1 on the vascular structural remodeling in spontaneous hypertensive rats (SHRs) using an adenovirus injection to knock down or overexpress profilin-1 mRNA. As a control, blank adenovirus was injected into age-matched SHRs and Wistar-Kyoto rats (WKYs). We quantified arterial structural remodeling through morphological methods, with thoracic aortas stained with hematoxylin-eosin and picosirius red. Western blotting was performed to measure the protein expression of inducible nitric oxide synthase (iNOS) and p38 mitogen-activated protein kinase (p38), and peroxynitrite was quantified by immunohistochemical staining. Overexpression of profilin-1 significantly promoted aortic remodeling, including an increase in vessel size, wall thickness, and collagen content, whereas the knockdown of profilin-1 could reverse these effects. In addition, the expression of phosphorylated p38, iNOS and peroxynitrite was significantly upregulated in SHRs with profilin-1 overexpression along with an increased level of interleukin- 6 (IL-6). These changes could be reversed by knockdown of profilin-1. Our results demonstrate a crucial role for profilin-1 in hypertension-induced arterial structural remodeling at least in part through the p38-iNOS-peroxynitrite pathway.

Composition of intraperitoneally implanted electrospun conduits modulates cellular elastic matrix generation

Improving elastic matrix generation is critical to developing functional tissue engineered vascular grafts. Therefore, this study pursued a strategy to grow autologous tissue in vivo by recruiting potentially more elastogenic cells to conduits implanted within the peritoneal cavity. The goal was to determine the impacts of electrospun conduit composition and hyaluronan oligomer (HA-o) modification on the recruitment of peritoneal cells, and their phenotype and ability to synthesize elastic matrix. These responses were assessed as a function of conduit intra-peritoneal implantation time. This study showed that the blending of collagen with poly(ε-caprolactone) (PCL) promotes a faster wound healing response, as assessed by trends in expression of macrophage and smooth muscle cell (SMC) contractile markers and in matrix deposition, compared to the more chronic response for PCL alone. This result, along with the increase in elastic matrix production, demonstrates the benefits of incorporating as little as 25% w/w collagen into the conduit. In addition, PCR analysis demonstrated the challenges in differentiating between a myofibroblast and an SMC using traditional phenotypic markers. Finally, the impact of the tethered HA-o is limited within the inflammatory environment, unlike the significant response found previously in vitro. In conclusion, these results demonstrate the importance of both careful control of implanted scaffold composition and the development of appropriate delivery methods for HA-o.

Life-long caloric restriction reduces oxidative stress and preserves nitric oxide bioavailability and function in arteries of old mice

Aging impairs arterial function through oxidative stress and diminished nitric oxide (NO) bioavailability. Life-long caloric restriction (CR) reduces oxidative stress, but its impact on arterial aging is incompletely understood. We tested the hypothesis that life-long CR attenuates key features of arterial aging. Blood pressure, pulse wave velocity (PWV, arterial stiffness), carotid artery wall thickness and endothelium-dependent dilation (EDD; endothelial function) were assessed in young (Y: 5-7 month), old ad libitum (Old AL: 30-31 month) and life-long 40% CR old (30-31 month) B6D2F1 mice. Blood pressure was elevated with aging (P < 0.05) and was blunted by CR (P < 0.05 vs. Old AL). PWV was 27% greater in old vs. young AL-fed mice (P < 0.05), and CR prevented this increase (P < 0.05 vs. Old AL). Carotid wall thickness was greater with age (P < 0.05), and CR reduced this by 30%. CR effects were associated with amelioration of age-related changes in aortic collagen and elastin. Nitrotyrosine, a marker of cellular oxidative stress, and superoxide production were greater in old AL vs. young (P < 0.05) and CR attenuated these increase. Carotid artery EDD was impaired with age (P < 0.05); CR prevented this by enhancing NO and reducing superoxide-dependent suppression of EDD (Both P < 0.05 vs. Old AL). This was associated with a blunted age-related increase in NADPH oxidase activity and p67 expression, with increases in superoxide dismutase (SOD), total SOD, and catalase activities (All P < 0.05 Old CR vs. Old AL). Lastly, CR normalized age-related changes in the critical nutrient-sensing pathways SIRT-1 and mTOR (P < 0.05 vs. Old AL). Our findings demonstrate that CR is an effective strategy for attenuation of arterial aging.

Association of linear ¹⁸F-sodium fluoride accumulation in femoral arteries as a measure of diffuse calcification with cardiovascular risk factors: a PET/CT study

BACKGROUND

The aim of this study was to correlate linear (18)F-sodium fluoride accumulation in the femoral arteries as a measure of diffuse mineral deposition in medial elastocalcinosis with cardiovascular risk factors (RFs) and calcified plaque burden (CPB).

METHODS AND RESULTS

In this study, 409 patients were examined by (18)F-sodium fluoride positron emission tomography/computed tomography (PET/CT). Tracer accumulation was analyzed both qualitatively and semiquantitatively by measuring the target-to-background ratio, and compared with cardiovascular RFs and CPB. Linear (18)F-sodium fluoride accumulation was observed in 159 (38.9%) patients and correlated significantly with age (P < .0001), hypertension (P < .0001), hypercholesterolemia (P = .0003), diabetes (P = .0003), history of smoking (P = .0007), prior cardiovascular events (P = .03), and CPB (P < .0001). The prevalence of linear tracer uptake increased as the number of cardiovascular RFs increased (P < .0001).

CONCLUSIONS

Linear (18)F-sodium fluoride uptake in the femoral arteries (1) provides a measure of diffuse mineral deposition, (2) demonstrates a highly significant correlation with cardiovascular RFs and CPB, and (3) is found to accumulate more frequently in patients with a high-risk profile for cardiovascular events. (18)F-sodium fluoride PET/CT may become a unique tool for in vivo visualization and quantification of ongoing calcification in large arteries.

Impact of electrospun conduit fiber diameter and enclosing pouch pore size on vascular constructs grown within rat peritoneal cavities

The generation of vascular grafts by recruiting autologous cells within the peritoneal cavity has shown promise. However, the microenvironment affects cell differentiation and elastic matrix production. Therefore, this study determined the impact of systematic changes in the average fiber diameter of electrospun poly(ɛ-caprolactone) conduits, and the pore size of pouches used to enclose the conduits, on recruited cells. After 2 weeks in the peritoneal cavity, fibrous capsules formed containing macrophages, α-smooth muscle actin (α-SMA)(+) and SM22α(+) myofibroblastic or smooth muscle like-cells, and what appeared to be mesothelial cells on the outer surfaces. These cells infiltrated and deposited matrix (e.g., collagen, hyaluoronan, and limited elastin) within conduit walls. Constructs enclosed within the largest pore pouches exhibited significantly better tissue generation responses (e.g., better cell infiltration, elongation, and matrix deposition). Additionally, the healing response was impacted by the conduit average fiber diameter, and consequently, the effective pore diameter, with the largest diameter fibers promoting the most positive healing response (e.g., greater total cellularity, extracellular matrix deposition, and α-SMA(+) cells). Six weeks post-intra-aortal grafting, constructs were occluded, but significant remodeling also occurred in the arterial microenvironment. Overall, these results demonstrate the importance of microenvironmental cues on recruited peritoneal cells and the necessity of developing strategies to further improve elastic matrix synthesis.

Tissue engineering and regenerative strategies to replicate biocomplexity of vascular elastic matrix assembly

Cardiovascular tissues exhibit architecturally complex extracellular matrices, of which the elastic matrix forms a major component. The elastic matrix critically maintains native structural configurations of vascular tissues, determines their ability to recoil after stretch, and regulates cell signaling pathways involved in morphogenesis, injury response, and inflammation via biomechanical transduction. The ability to tissue engineer vascular replacements that incorporate elastic matrix superstructures unique to cardiac and vascular tissues is thus important to maintaining vascular homeostasis. However, the vascular elastic matrix is particularly difficult to tissue engineer due to the inherently poor ability of adult vascular cells to synthesize elastin precursors and organize them into mature structures in a manner that replicates the biocomplexity of elastic matrix assembly during development. This review discusses current tissue engineering materials (e.g., growth factors and scaffolds) and methods (e.g., dynamic stretch and contact guidance) used to promote cellular synthesis and assembly of elastic matrix superstructures, and the limitations of these approaches when applied to smooth muscle cells, the primary elastin-generating cell type in vascular tissues. The potential application of these methods for in situ regeneration of disrupted elastic matrix at sites of proteolytic vascular disease (e.g., abdominal aortic aneurysms) is also discussed. Finally, the review describes the potential utility of alternative cell types to elastic tissue engineering and regenerative matrix repair. Future progress in the field is contingent on developing a thorough understanding of developmental elastogenesis and then mimicking the spatiotemporal changes in the cellular microenvironment that occur during that phase. This will enable us to tissue engineer clinically applicable elastic vascular tissue replacements and to develop elastogenic therapies to restore homeostasis in de-elasticized vessels.

Aligned electrospun scaffolds and elastogenic factors for vascular cell-mediated elastic matrix assembly

Strategies to enhance the production of organized elastic matrix by smooth muscle cells (SMCs) are critical in engineering functional vascular conduits. Therefore, the goal of this study was to determine the effect of different surfaces, i.e. random and aligned electrospun poly(ε-caprolactone) meshes and two-dimensional (2D) controls, and exogenous elastogenic factors on the cultured rat aortic SMC phenotype and production of extracellular matrix. This study demonstrated that aligned electrospun fibres guide cell alignment, induce a more elongated cell morphology and promote a more synthetic phenotype. Importantly, these cells produced greater amounts of elastin-rich matrix per cell on the electrospun scaffolds. In addition, exogenous elastogenic factors severely limited rat aortic smooth muscle cells (RASMCs) proliferation and promoted a more synthetic SMC phenotype on electrospun meshes, but they had less effect on 2D controls. Finally, the elastogenic factors induced the SMCs to generate more matrix collagen and elastin on a per cell basis. Together, these results demonstrate the elastogenic benefits of electrospun meshes.

Evaluating arterial aging in the clinical setting: a tentative agenda for critical appraisal

Population aging is a worldwide phenomenon. However, the cultural attitude to older adults has not yet incorporated understanding of the effects of the aging process. The arterial system is affected by the aging process, which is responsible for the great majority of mortality, morbidity and disability in older people. We briefly describe how the aging process affects large arteries and their properties that are easily measurable noninvasively, and suggest a tentative agenda for solving the critical problems that have hampered the diffusion of routine assessment of arterial aging in the clinical setting.

Histomorphology and vascular lesions in dorsal rat skin used as injection sites for a subcutaneous toxicity study

Subcutaneous injection of pharmaceutical compounds into the dorsal skin of rats is common in preclinical and nonclinical studies. However, no detailed histologic description of this anatomic location has been published to date. Following the observation of vascular lesions in the dorsum of rats in a thirteen-week toxicity study, a complementary study was performed on untreated Sprague-Dawley rats to evaluate the normal histology of the skin and subcutis, the potential effect of chronic subcutaneous injection on the morphology of the skin and its vasculature, and the spontaneous vascular pathology in the areas used as injection sites in the principal study. This study showed that saline injection did not fundamentally alter the morphology of the injection sites used for the principal study. Skin thickness was greater in males than in females. Although acellular intimal thickening occurred spontaneously in the dorsal skin of untreated males and females, only males had a spontaneous incidence of intimal hyperplasia. No site predilection for intimal lesions was apparent for either sex. Saline injection, or the physical trauma of injection, may induce intimal hyperplasia; males appear more likely to develop the lesion than do females. It is possible that acellular intimal thickening can progress to intimal hyperplasia under appropriate conditions.

Polyphenol-stabilized tubular elastin scaffolds for tissue engineered vascular grafts

Tissue-engineered vascular grafts require elastic, acellular porous scaffolds with controlled biodegradability and properties matching those of natural arteries. Elastin would be a desirable component for such applications, but elastin does not easily regenerate experimentally. Our approach is to develop tubular elastin scaffolds using decellularization and removal of collagen from porcine carotid arteries ( approximately 5 mm diameter) using alkaline extraction. Because elastin is susceptible to rapid degeneration after implantation, scaffolds were further treated with penta-galloyl glucose (PGG), an established polyphenolic elastin-stabilizing agent. Scaffolds were compared in vitro with detergent-decellularized arteries for structure, composition, resistance to degradation, mechanical properties, and cytotoxicity and in vivo for cell infiltration and remodeling potential. Results showed effective decellularization and almost complete collagen removal by alkaline extraction. PGG-treated elastin scaffolds proved to be resistant to elastase digestion in vitro, maintained their cylindrical shapes, showed high resistance to burst pressures, and supported growth of endothelial cells and fibroblasts. In vivo results showed that PGG treatment reduced the rate of elastin biodegradation and controlled cell infiltration but did not hamper new collagen and proteoglycan deposition and secretion of matrix-degrading proteases. Alkali-purified, PGG-treated tubular arterial elastin scaffolds exhibit many desirable properties to be recommended for clinical applications as vascular grafts.

Serum phosphorus concentrations and arterial stiffness among individuals with normal kidney function to moderate kidney disease in MESA

BACKGROUND AND OBJECTIVES

Higher phosphorus levels are associated with cardiovascular disease (CVD) events and mortality. Whether vascular stiffness may be responsible is unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study examined the cross-sectional associations of serum phosphorus with ankle brachial index (ABI), pulse pressure, and large and small artery elasticity by radial artery waveform analysis among 1370 individuals (440 with moderate chronic kidney disease) who did not have clinical CVD and participated in the Multi-Ethnic Study of Atherosclerosis.

RESULTS

Fifty-nine (4%) individuals had high ABI (>1.30), a marker of peripheral arterial stiffness. Participants with phosphorus levels >4 mg/dl had greater than four-fold risk for high ABI compared with participants with phosphate levels <3 mg/dl (relative risk 4.6; 95% confidence interval 1.6 to 13.2; P = 0.01) after adjustment for demographics, traditional CVD risk factors, and kidney function. Higher phosphorus levels were also associated with greater pulse pressure and lesser large and small artery elasticity in unadjusted models, but these associations were attenuated after adjustment.

CONCLUSIONS

Higher phosphorus levels are strongly associated with high ABI but not pulse pressure or large or small artery elasticity. If confirmed in future studies, then the association of higher phosphorus concentrations with CVD events may be partially mediated through peripheral arterial stiffness.

Aortic correlates of clinical markers of large artery structure and function. Effects of aging and hypertension

BACKGROUND AND AIMS

Non-invasive measures of large artery structure and function--such as aorto-femoral pulse wave velocity (PWV), arterial compliance (AC) and common carotid intima-media thickness (CCA IMT)--can predict new CV events, independently of traditional CV risk factors. However, neither their relations with aorta properties nor the effects of aging and hypertension on those relations are yet clear.

METHODS AND RESULTS

40 subjects (18 M, 22 F; mean age 60+/-16 yrs, range 21-83 yrs) free of any acute CV event, valve disease or atrial fibrillation, were studied. Aortic IMT, diastolic diameter (D) and distensibility (Dist) were measured by transesophageal echocardiography at three different levels: ascending aorta (AA), distal aortic arch (Aarc) and descending aorta (DA). PWV was measured by Complior. AC was measured as the ratio of stroke volume to pulse pressure. CCA IMT was measured by ultrasonography in diastole. The Dist, IMT, and D of each aortic segment were introduced alternatively into the regression models. After controlling for age, sex, traditional risk factors and prevalent CV disease, AC showed a significant positive association with the distensibility of proximal aortic segments, but no significant association with properties of distal aorta; PWV showed a significant positive association with proximal aorta wall thickness and a negative association with distal aorta distensibility; CCA IMT was positively associated with distal aorta wall thickness, but not with any explored property of the proximal aorta. None of these relationships differed between younger or older, normotensive or hypertensive subjects.

CONCLUSIONS

Non-invasive measures of large artery structure and function are not equivalent with respect to their relations with aortic properties, so that AC seems to reflect proximal aorta function, PWV proximal aorta structure and distal aorta function, and CCA IMT distal aorta structure. Future studies are needed to confirm whether these relations identify a common pathogenetic mechanism, which may be the target for new therapeutic strategies.

Aging, smooth muscle cells and vascular pathobiology: Implications for atherosclerosis

Epidemiological and autopsy studies suggest a close link between aging and the clinical manifestation of atherosclerosis. Several experiments show increased arterial susceptibility to atherogenetic stimuli in aged subjects. All together, these findings support the concept that aging represents an independent atherogenetic risk factor, intimately associated to other parietal, microenvironmental and systemic noxae. Smooth muscle cells (SMCs) represent the major arterial cell population. As aging occurs, SMCs progressively migrate from the tunica media and accumulate into the tunica intima. Myointimal thickening may represent the site where low-grade atherogenic stimuli cause early development and more severe lesion progression. Intimal SMC accumulation is characterized from a switch, from a differentiated to a synthetic phenotype, with reduced myocytic cytoskeletal markers and the expression of new proteins. Aging also associates to changes of SMC proliferative and apoptotic behavior and response to growth factors, such as transforming growth factor-beta1. The alteration of SMC properties represents a crucial event in the pathobiology of arterial wall, since it contributes to the vascular remodeling and decline of function with aging and favors the progression of atherosclerosis. Increased knowledge of biomolecular mechanisms regulating these events helps to develop new strategies aimed at contrasting the adverse effect of vascular aging.

Dilation and reduced distensibility of rat carotid artery with aging

To better understand the pathogenesis of increased arterial stiffening with aging, the relative contribution of geometry (lumen diameter) and stiffening of wall components (elastic modulus) to reduced distensibility of rat carotid artery in the early stages of aging was investigated. Pressure-volume (distensibility) relationships were measured in excised, in vitro perfused right carotid artery of 7-. 10- and 20-month old, male Sprague-Dawley rats. The left carotid artery of rats was perfusion-fixed in situ at 100 mm Hg and then embedded in epoxy for morphometric measurements. Compared to 7- and 10-month old rats, there was dilation (increased lumen diameter), increased wall thickness, and reduced distensibility and unchanged elastic moduli of carotid artery in 20-month old rats. Dilation (with early recruitment of collagen fibrils during pressure rise) rather than increased stiffness of wall components appears to be the cause of reduced distensibility of rat carotid artery in the early stages of aging.

Oxidative stress in atherogenesis and arterial thrombosis: the disconnect between cellular studies and clinical outcomes

Atherosclerosis is a multifactorial disease for which the molecular etiology of many of the risk factors is still unknown. As no single genetic marker or test accurately predicts cardiovascular death, phenotyping for markers of inflammation may identify the individuals at risk for vascular diseases. Reactive oxygen species (ROS) are key mediators of signaling pathways that underlie vascular inflammation in atherogenesis, starting from the initiation of fatty streak development through lesion progression to ultimate plaque rupture. Various animal models of atherosclerosis support the notion that ROS released from NAD(P)H oxidases, xanthine oxidase, lipoxygenases, and enhanced ROS production from dysfunctional mitochondrial respiratory chain indeed have a causatory role in atherosclerosis and other vascular diseases. Human investigations also support the oxidative stress hypothesis of atherogenesis. This is further supported by the observed impairment of vascular function and enhanced atherogenesis in animal models that have deficiencies in antioxidant enzymes. The importance of oxidative stress in atherosclerosis is further emphasized because of its role as a unifying mechanism across many vascular diseases. The main contraindicator for the role oxidative stress plays in atherosclerosis is the lack of effectiveness of antioxidants in reducing primary endpoints of cardiovascular death and morbidity. However, this lack of effectiveness by itself does not negate the existence or causatory role of oxidative stress in vascular disease. Lack of proven markers of oxidative stress, which could help to identify a subset of population that can benefit from antioxidant supplementation, and the complexity and subcellular localization of redox reactions, are among the factors responsible for the mixed outcomes in the use of antioxidants for the prevention of cardiovascular diseases. To better understand the role of oxidative stress in vascular diseases, future studies should be aimed at using advances in mouse and human genetics to define oxidative stress phenotypes and link phenotype with genotype.

Use of cardiovascular medications in the elderly

Cardiovascular disease is the leading cause of death in patients aged 65 and above. Although elderly persons represent only 12.4% of the US population, they account for about a third of drug expenditures. However the appropriate use of cardiovascular medications in these patients has been shown to reduce the rate of cardiovascular morbidity and mortality. The normal aging and the disease process in the elderly result in significant changes at the structural and molecular level in the elderly. The changes that take place in the autonomic nervous system, the kidneys, and the liver in the elderly modify the metabolism and clinical effects of most medications. Elderly patients are also susceptible to side effects and adverse drug reactions. Physicians should have a clear understanding of the normal aging processes, the abnormal changes due to disease process and the changes in the pharmacology of drugs in the elderly to deliver proper care to the elderly patient.

Perspectives on mammalian cardiovascular aging: humans to molecules

Age-related changes in cardiovascular function and structure in healthy adult volunteer community dwelling subjects (from 20 to 85 years) is remarkable for changes in pump function [impaired left ventricular (LV) ejection reserve capacity manifest by a reduced ejection fraction and accompanied by diminished cardioacceleration, LV dilation at end diastole and an altered diastolic filling pattern] and increased vascular afterloading. There is also evidence for a reduction in the number of cardiac myocytes with advancing age. Subcellular changes with aging (best understood in rodents) include certain regulatory factors of excitation-contraction-relaxation coupling (i.e. calcium handling), modulation by adrenergic receptor (AR) stimulation, and changes in the generation and sensitivity to the damaging effects of ROS. Coordinated changes in gene expression and/or protein function with aging result in a prolonged action potential (AP), Ca(i) transient, and contraction. L-type Ca(2+) current (I(Ca)) inactivates more slowly, and outwardly-directed K(+) currents are reduced, and likely contribute to AP-prolongation. The rate of Ca(2+) sequestration by the sarcoplasmic reticulum (SR) decreases in the senescent myocardium, in part underlying the prolonged Ca(i) transient. An age-associated reduction in transcription of the SERCA2 gene, coding for the SR Ca(2+) pump, accounts in part for a decrease in the SR pump site density. The contractile response to both beta(1)-AR and beta(2)-AR stimulation diminishes with aging due to decreased adrenergic augmentation of I(Ca), and thus the Ca(i) transient, in senescent vs. young hearts. The age-associated reduction in the postsynaptic response of myocardial cells to beta(1)-AR stimulation appears to be due to multiple changes in molecular and biochemical receptor coupling and post-receptor mechanisms. An increased basal production of ROS is paralleled by increased ROS-sensitivity, markers of chronic ROS damage and mitochondrial functional decline. Overall, these changes lead to a diminished (but not necessarily exhausted) capacity of the heart to adapt to physiological or pathological stress with advancing age.

Age-associated cardiovascular changes in health: impact on cardiovascular disease in older persons

In the United States, cardiovascular disease, e.g., atherosclerosis and hypertension, that lead to heart failure and stroke, is the leading cause of mortality, accounting for over 40 percent of deaths in those aged 65 years and above. Over 80 percent of all cardio-vascular deaths occur in the same age group. Thus, age, per se, is the major risk factor for cardiovascular disease. Clinical manifestations and prognosis of these cardiovascular diseases likely become altered in older persons with advanced age because interactions occur between age-associated cardiovascular changes in health and specific pathophysiologic mechanisms that underlie a disease. A fundamental understanding of age-associated changes in cardiovascular structure and function ranging in scope from humans to molecules is required for effective and efficient prevention and treatment of cardiovascular disease in older persons. A sustained effort over the past two decades has been applied to characterize the multiple effects of aging in health on cardiovascular structure and function in a single study population, the Baltimore Longitudinal Study on Aging. In these studies, community dwelling, volunteer participants are rigorously screened to detect both clinical and occult cardiovascular disease and characterized with respect to lifestyle, e.g. exercise habits, in an attempt to deconvolute interactions among lifestyle, cardiovascular disease and the aging process in health. This review highlights some specific changes in resting cardiovascular structure and function and cardiovascular reserve capacity that occur with advancing age in healthy humans. Observations from relevant experiments in animal models have been integrated with those in humans to provide possible mechanistic insight.

Effects of aging and blood pressure on the structure of the thoracic aorta in SAM mice: a model of age-associated degenerative vascular changes

The effects of aging and blood pressure on the structural alterations of the thoracic aorta were examined using male, accelerated senescence-prone, short-lived SAMP11 mice or accelerated senescence-resistant, long-lived SAMR1 mice. The aortic wall thickness increased significantly by 34% in SAMR1 and by 62% in SAMP11 with advanced age. We observed branching, breakage and disorganization of the elastic lamellae, an increase in thin collagen fibrils between the medial smooth muscle cells and hypertrophy but a significant decrease in the number of medial smooth muscle cells with aging in both strains. These alterations observed in SAMP11 occurred earlier and were more exaggerated with advanced age than in SAMR1. The aortic lumen dilated gradually in SAMR1, but narrowed significantly in SAMP11 with aging. The systolic blood pressure did not differ significantly among SAMP11s aged 3-9months, or among all ages of SAMR1. However, it was elevated in SAMP11 at the terminal stage of their life. Our results suggest that the aorta in SAMR1 might reflect the physiological process of aging, whereas SAMP11 showed earlier changes due to the senescence acceleration of the vascular cells, which were exaggerated by the elevated blood pressure.

Research Agenda for Cardiovascular Aging: Humans to Molecules

Clinical manifestations of specific cardiovascular diseases, e.g., atherosclerosis and hypertension, that lead to heart failure and stroke likely become altered in older persons of advanced age because interactions occur between age-associated cardiovascular changes in health and specific pathophysiologic mechanisms that underlie cardiovascular diseases. The interactions result in a lower threshold for clinical symptoms, and greater severity and poorer prognosis of these diseases in older vs. younger persons. In this regard, cardiovascular changes that occur during aging in health ought not to be considered to reflect a "normal process"; rather these specific age-associated changes must be construed as specific "risk factors" for the aforementioned cardiovascular diseases and ought to become targets of interventions designed to prevent the epidemic of cardiovascular disease in later life. Such a strategy would thus advocate preventive treatment for what is now considered to be "normal cardiovascular aging." Effective and efficient prevention of the "risks" associated with cardiovascular aging in apparent health requires a fundamental understanding of these changes ranging in scope from humans to molecules. An opinion regarding specific directions for research aimed toward the achievement of this understanding is provided. (c) 2000 by CVRR, Inc.

The effect of caloric restriction on the aortic tissue of aging rats

Connective tissue shows peculiar and complex age-related modifications, which can be, at least in part, responsible for altered functions and increased susceptibility to diseases. Food restriction has long been known to prolong life in rodents, having antiaging effects on a variety of physiologic and pathologic processes. Therefore, the aorta has been investigated in rats fed normal or hypocaloric diet, from weaning to senescence. Compared with controls, caloric-restricted animals showed less pronounced age-dependent alterations such as elastic fiber degradation, collagen accumulation and cellular modifications. Immunocytochemical analyses revealed that elastic fibers were positively labelled for biglycan, decorin, ApoB100 (LDL), ApoA1 (HDL) and elastase and that the intensity of the reactions was time- and diet-dependent. With age, the major changes affecting aortic elastic fibers were increased positivity for decorin, LDL and elastase. Compared with age-matched normal fed rats, caloric restricted animals revealed lower content of LDL, decorin and elastase and higher positivity for HDL. These data suggest that a caloric restricted diet might influence the aging process of the arterial wall in rats, delaying the appearance of age-related degenerative features, such as structural alterations of cells and matrix and modified interactions of elastin with cells and with other extracellular matrix molecules.

Age-related changes in the signaling and function of vascular smooth muscle cells

Aging is an independent risk factor for the development of atherosclerosis, a vascular abnormality that plays a significant role in the development of many cardiovascular disorders. Animal experiments have demonstrated that aging predisposes the vasculature to advanced atherosclerotic disease and vessel injury and that this predisposition is a function of age-associated changes in the vessel wall itself. Because vascular smooth muscle cells play important roles in the pathogenesis of many vascular disorders, identifying age-associated differences in the way these cells respond to extracellular clues has been an area of active research. Currently, the most remarkable differences in intracellular signaling between vascular smooth muscle cells isolated from young and old animals are related to the control of cell migration through the CamKII pathways and the accelerated transition of older vascular smooth muscle cells from the contractile to the synthetic phenotype. These differences may be due to alternative signaling pathways revealed by the inability of older cells to respond to inhibitors, such as transforming growth factor (TGF)-beta1, or to altered interactions with the extracellular matrix resulting from age-associated shifts in integrin expression or changes in the matrix composition of blood vessels. The exact role that these alterations have in explaining age-associated differences in the response of the vessel wall to injury and its increased susceptibility to developing advanced atherosclerotic lesions remains to be determined but will be guided by studies on intracellular signaling mechanisms.

Accumulation of advanced glycation endproducts in the rat nephron: link with circulating AGEs during aging

The accumulation of advanced glycosylation end products (AGEs) is believed to be a factor in the development of aging nephropathy. We have attempted to establish a link between the formation of AGEs and the onset of renal impairment with aging, indicated by albuminuria, using a fluorescence assay and immunohistochemical detection of AGEs in the renal extracellular matrix in rats. The fluorescence of collagenase-digested Type IV collagen from GBM increased with age, from 1.65 +/- 0.05 AU/mM OHPro (3 months) and 1.58 +/- 0.04 (10 months) to 2.16 +/- 0.06 (26 months) (p < 0.001) and 2.53 +/- 0.18 (30 months) (p < 0.001). In contrast, the extent of early glycation products significantly decreased from 5.35 +/- 0.25 nmol HCHO/nmol OHPro at 3 months to 3.14 +/- 0.19 at 10 months (p < 0.001), 3.42 +/- 0.38 at 26 months, and 0.74 +/- 0.08 at 30 months (p < 0.001). The urinary fluorescence of circulating AGE rose from 2.42 +/- 0.15 AU/mg protein (3 months), 1.69 +/- 0.07 (10 months), to 4.63 +/- 0.35 (26 months) (p < 0.01) and 4.73 +/- 0.72 (30 months), while the serum fluorescence increased from 0.39 +/- 0.02 AU/mg protein at 3 months and 0.43 +/- 0.02 at 10 months to 0.59 +/- 0.04 at 26 months (p < 0.001) and 0.54 +/- 0.03 at 30 months (p < 0.04). Polyclonal antibodies raised against AGE RNase showed faint areas of AGE immunoreactivity in mesangial areas in the nephrons of young rats. The immunolabeling of Bowman's capsule, the mesangial matrices, and the peripheral loops of glomerular and tubule basement membranes increased with rat age. The increase in circulating AGE peptides parallels the accumulation of AGEs in the nephron, and this parallels the pattern of extracellular matrix deposition, suggesting a close link between AGE accumulation and renal impairment in aging rats.

Alpha 1-adrenoceptor vasoconstriction in the tail artery during ageing

1. We have studied the alpha 1-adrenoceptor-mediated responses in intact tail artery rings from 3-4 and 20-22 months old Sprague-Dawley rats, focusing on possible endothelial alterations. The influence of nitric oxide released by the endothelium, the number of alpha 1-adrenoceptors and the functional receptor reserve were evaluated to determine their contribution to the contractile response mediated by this receptor. The state of the endothelial layer was assessed by confocal microscopy. 2. Noradrenaline (1 nM-100 microM) induced concentration-dependent vasoconstriction. The maximum contractions to noradrenaline (P < 0.05) and to 75 mM KCl (P < 0.01) were higher in young than in old animals. 3. The density (Bmax) of alpha 1-adrenoceptors and the dissociation constant (KD) obtained in [3H]-prazosin binding experiments were unchanged by age. 4. The apparent affinity (pKA) and the percentage of functional receptors (qx 100) remaining after phenoxybenzamine (0.03 microM) were similar in both age groups. 5. After partial alpha 1-adrenoceptor inactivation with phenoxybenzamine, NG-nitro-L-arginine methylester (30 microM) significantly potentiated the E/[A] curve to noradrenaline in young rats. However, only responses to 0.1 to 1 microM noradrenaline were significantly potentiated in old animals. In addition, 94% of the vessels from young, but only 52% from old rats were relaxed by 80-100% of the noradrenaline (0.03 microM) contraction, with 1 microM acetylcholine. 6. No modifications in the area (micron2) or in the number of endothelial nuclei (per mm2) were observed between age groups. An elongation of the nuclei of endothelial cells was observed in the old animals. 7. These data suggest that the noradrenaline-induced contraction is decreased in old rats probably due to differences in either the contractile machinary or postreceptor mechanisms. These alterations may be accompanied by an impairment of the release or production of NO from endothelial cells.