Aging impairs flow-induced dilation in coronary arterioles: role of NO and H(2)O(2)

Ageing impairs endothelium-dependent vasodilatation and alters redox signalling in diaphragm arterioles from male and female Fischer-344 rats

Diaphragm hyperaemia and regional blood flow distribution are impaired with ageing, potentially consequent to altered vascular structure and/or diminished vasomotor function. Evidence from locomotory skeletal muscle suggests that age-related diaphragm vasomotor dysfunction may be related to a blunted endothelium-mediated vasodilatation, decreased nitric oxide (NO) bioavailability and/or augmented reactive oxygen species (ROS) generation. We hypothesized that, in the medial costal diaphragm with old age, there would be fewer feed arteries (FAs) and impaired vasomotor function, via endothelium-specific mechanisms, in first-order (1A) arterioles. In young (Y) and old (O) Fischer-344 rats, the number of medial costal diaphragm FAs was quantified. 1A arterioles (117-220 µm) were isolated, cannulated and pressurized via hydrostatic reservoirs. Thereafter endothelium-dependent (via ACh) vasodilatory responses were assessed. In a separate set of arterioles, ACh-mediated dilatation was assessed before and after treatment with the superoxide dismutase mimetic Tempol (100 µm) and Tempol plus the hydrogen peroxide (H2O2) scavenger catalase (100 U/ml). The average number of medial costal FAs was lower in the rat diaphragm with old age (p = 0.001). Endothelium- and nitric oxide synthase (NOS)-dependent vasodilatation was 21% lower in medial costal 1A arterioles from O rats (p < 0.001). Tempol decreased ACh-mediated vasodilatation of medial costal 1A arterioles from Y and O rats but did not eliminate age-related differences. Tempol plus catalase further decreased ACh-mediated vasodilatation in O but not Y vessels. In the medial costal diaphragm vasculature, ageing is associated with (1) arterial rarefaction, (2) impaired endothelium-dependent vasodilatation via NOS- and ROS-dependent mechanisms and (3) increased reliance on ROS-mediated vasodilatation. KEY POINTS: Old age blunts the hyperaemic response and alters regional blood flow distribution in the diaphragm. The effect of ageing on vascular structure and function in respiratory skeletal muscle is unknown. In young and old Fischer-344 rats of both sexes, we quantified the number of feed arteries (FAs) and assessed the vasoreactivity of first-order (1A) arterioles in the medial costal diaphragm. The number of medial costal diaphragm FAs was lower in old rats. In 1A arterioles endothelium-dependent vasodilatation was blunted, and reactive oxygen species (ROS)-mediated vasodilatory signalling was greater in old rats. We found no evidence of sex differences in diaphragm macrovascular structure, endothelial function or ROS-mediated signalling in young or old rats. Our findings in the diaphragm vasculature with ageing provide a mechanistic basis for the age-related deficits in diaphragm blood flow capacity. Therapeutic interventions targeting the diaphragm vasculature to improve perfusion and oxygen delivery may reduce the burden of age-related diaphragm dysfunction.

The molecular mechanism of thrombospondin family members in cardiovascular diseases

Cardiovascular diseases have been identified as vital factors in global morbidity and mortality in recent years. The available evidence suggests that various cytokines and pathological proteins participate in these complicated and changeable diseases. The thrombospondin (TSP) family is a series of conserved, multidomain calcium-binding glycoproteins that cause cell-matrix and cell-cell effects via interactions with other extracellular matrix components and cell surface receptors. The TSP family has five members that can be divided into two groups (Group A and Group B) based on their different structures. TSP-1, TSP-2, and TSP-4 are the most studied proteins. Among recent studies and findings, we investigated the functions of several family members, especially TSP-5. We review the basic concepts of TSPs and summarize the relevant molecular mechanisms and cell interactions in the cardiovascular system. Targeting TSPs in CVD and other diseases has a remarkable therapeutic benefit.

Functional, Structural and Proteomic Effects of Ageing in Resistance Arteries

The normal ageing process affects resistance arteries, leading to various functional and structural changes. Systolic hypertension is a common occurrence in human ageing, and it is associated with large artery stiffening, heightened pulsatility, small artery remodeling, and damage to critical microvascular structures. Starting from young adulthood, a progressive elevation in the mean arterial pressure is evidenced by clinical and epidemiological data as well as findings from animal models. The myogenic response, a protective mechanism for the microcirculation, may face disruptions during ageing. The dysregulation of calcium entry channels (L-type, T-type, and TRP channels), dysfunction in intracellular calcium storage and extrusion mechanisms, altered expression of potassium channels, and a change in smooth muscle calcium sensitization may contribute to the age-related dysregulation of myogenic tone. Flow-mediated vasodilation, a hallmark of endothelial function, is compromised in ageing. This endothelial dysfunction is related to increased oxidative stress, lower nitric oxide bioavailability, and a low-grade inflammatory response, further exacerbating vascular dysfunction. Resistance artery remodeling in ageing emerges as a hypertrophic response of the vessel wall that is typically observed in conjunction with outward remodeling (in normotension), or as inward hypertrophic remodeling (in hypertension). The remodeling process involves oxidative stress, inflammation, reorganization of actin cytoskeletal components, and extracellular matrix fiber proteins. Reactive oxygen species (ROS) signaling and chronic low-grade inflammation play substantial roles in age-related vascular dysfunction. Due to its role in the regulation of vascular tone and structural proteins, the RhoA/Rho-kinase pathway is an important target in age-related vascular dysfunction and diseases. Understanding the intricate interplay of these factors is crucial for developing targeted interventions to mitigate the consequences of ageing on resistance arteries and enhance the overall vascular health.

Effects of high-intensity interval training on cardiac remodelling, function and coronary microcirculation in de novo heart transplant patients: a substudy of the HITTS randomised controlled trial

Objectives

High-intensity interval training (HIT) improves peak oxygen consumption (VO2peak) in de novo heart transplant (HTx) recipients. It remains unclear whether this improvement early after HTx is solely dependent on peripheral adaptations, or due to a linked chain of central and peripheral adaptations. The objective of this study was to determine whether HIT results in structural and functional adaptations in the cardiovascular system.

Methods

Eighty-one de novo HTx recipients were randomly assigned to participate in either 9 months of supervised HIT or standard care exercise-based rehabilitation. Cardiac function was assessed by echocardiogram and the coronary microcirculation with the index of microcirculatory resistance (IMR) at baseline and 12 months after HTx.

Results

Cardiac function as assessed by global longitudinal strain was significantly better in the HIT group than in the standard care group (16.3±1.2% vs 15.6±2.2%, respectively, treatment effect = -1.1% (95% CI -2.0% to -0.2%), p=0.02), as was the end-diastolic volume (128.5±20.8 mL vs 123.4±15.5 mL, respectively, treatment effect=4.9 mL (95% CI 0.5 to 9.2 mL), p=0.03). There was a non-significant tendency for IMR to indicate improved microcirculatory function (13.8±8.0 vs 16.8±12.0, respectively, treatment effect = -4.3 (95% CI -9.1 to 0.6), p=0.08).

Conclusion

When initiated early after HTx, HIT leads to both structural and functional cardiovascular adaptations.

Trial registration number

NCT01796379.

Evaluation of coronary microvascular dysfunction and risk factors in children and youth with Turner syndrome by magnetic resonance myocardial perfusion imaging

OBJECTIVE

Turner syndrome (TS) has an increased predisposition to ischaemic heart disease and the status of coronary microcirculation in TS is largely unknown. This study aims to evaluate myocardial microvascular function in TS using first-pass magnetic resonance perfusion imaging and determine significant risk factors contributing to microvascular dysfunction in the early stage.

DESIGN

Perspective cohort study.

PATIENTS

The study cohort consisted of 67 children and youth with TS and 32 age- and gender-matched controls. Measurements Clinical characteristics, left ventricle (LV) volume and function and cardiovascular magnetic resonance-derived myocardial perfusion parameters were assessed. Univariable and multivariable linear regression analyses were performed to assess the potential risk factors for microvascular dysfunction.

RESULT

Microvascular perfusion decreased in TS in global and segmented myocardium as reflected in the lower upslope_cor and maximum signal intensity (MaxSI) of LV myocardium compared to controls. Multivariable linear regression analysis indicated that age (β = -0.107, 95% confidence interval [CI] = -0.201 to -0.013, p = .026) and being overweight/obese (β = -1.155, CI = -2.134 to -0.176, p = .021) were independent impact factors of microvascular dysfunction. Subgroup analysis showed the upslope_cor of older patients with TS decreased more significantly compared with that of normal controls. Upslope_cor and MaxSI were lower in overweight/obese patients with TS than in patients with normal body mass index (BMI) and controls.

CONCLUSION

Myocardial microvascular dysfunction can occur in children and youth patients with TS. Age and overweight/obesity were the independent risk factors of microvascular dysfunction, which imply the importance of lowering BMI for the prevention of coronary heart disease in young TS population.

The Effect of Ticagrelor on Endothelial Function Compared to Prasugrel, Clopidogrel, and Placebo: A Systematic Review and Meta-Analysis

Background/Objective

Endothelial dysfunction is associated with the long-term outcomes in patients with coronary artery disease (CAD). Recent evidence suggests that ticagrelor, a potent antiplatelet agent, improves endothelial function. However, several studies demonstrated contrasting results. The objective of this meta-analysis was to determine the efficacy of ticagrelor treatment on endothelial function.

Materials and Methods

A systematic literature study was conducted on databases including PubMed, Web of Science, EMBASE, Scopus, and the Cochrane Library. A historical search was performed for a reference list of the selected studies as of August 2021. The randomized controlled trials (RCTs) were assessed using the Cochrane tool. The weighted mean difference (WMD) 95% CI was treated as the overall effect size, and data were pooled using the fixed-effect model or random-effect model according to the heterogeneity. Subgroup and sensitivity analyses were performed to measure the effects of potential confounders.

Results

A total of 21 studies were included. The meta-analysis indicated that ticagrelor resulted in a significant increase of flow-mediated dilation (FMD) (WMD: 1.48; 95% CI: 0.36, 2.60), reactive hyperemia index (RHI) (WMD: 0.06; 95% CI: 0.00, 0.13), and circulating progenitor endothelial cells (CEPCs) (WMD: 13.84; 95% CI: 5.70, 21.98), and a reduction in the index of microvascular resistance (IMR) (WMD: −15.39; 95% CI: −25.11, −5.68).

Conclusion

Ticagrelor has a significant effect on some markers of endothelial function in patients with CAD. However, the results should be interpreted with caution due to the heterogeneity and limited studies.

Mechanobiology of Microvascular Function and Structure in Health and Disease: Focus on the Coronary Circulation

The coronary microvasculature plays a key role in regulating the tight coupling between myocardial perfusion and myocardial oxygen demand across a wide range of cardiac activity. Short-term regulation of coronary blood flow in response to metabolic stimuli is achieved via adjustment of vascular diameter in different segments of the microvasculature in conjunction with mechanical forces eliciting myogenic and flow-mediated vasodilation. In contrast, chronic adjustments in flow regulation also involve microvascular structural modifications, termed remodeling. Vascular remodeling encompasses changes in microvascular diameter and/or density being largely modulated by mechanical forces acting on the endothelium and vascular smooth muscle cells. Whereas in recent years, substantial knowledge has been gathered regarding the molecular mechanisms controlling microvascular tone and how these are altered in various diseases, the structural adaptations in response to pathologic situations are less well understood. In this article, we review the factors involved in coronary microvascular functional and structural alterations in obstructive and non-obstructive coronary artery disease and the molecular mechanisms involved therein with a focus on mechanobiology. Cardiovascular risk factors including metabolic dysregulation, hypercholesterolemia, hypertension and aging have been shown to induce microvascular (endothelial) dysfunction and vascular remodeling. Additionally, alterations in biomechanical forces produced by a coronary artery stenosis are associated with microvascular functional and structural alterations. Future studies should be directed at further unraveling the mechanisms underlying the coronary microvascular functional and structural alterations in disease; a deeper understanding of these mechanisms is critical for the identification of potential new targets for the treatment of ischemic heart disease.

Coronary microvascular adaptations distal to epicardial artery stenosis

Until recently, epicardial coronary stenosis has been considered the primary outcome of coronary heart disease, and clinical interventions have been dedicated primarily to the identification and removal of flow-limiting stenoses. However, a growing body of literature indicates that both epicardial stenosis and microvascular dysfunction contribute to damaging myocardial ischemia. In this review, we discuss the coexistence of macro- and microvascular disease, and how the structure and function of the distal microcirculation is impacted by the hemodynamic consequences of an epicardial, flow-limiting stenosis. Mechanisms of endothelial dysfunction as well as alterations of smooth muscle function in the coronary microcirculation distal to stenosis are discussed. Risk factors including diabetes, metabolic syndrome, and aging exacerbate microvascular dysfunction in the myocardium distal to a stenosis, and our current understanding of the role of these factors in limiting collateralization and angiogenesis of the ischemic myocardium is presented. Importantly, exercise training has been shown to promote collateral growth and improve microvascular function distal to stenosis; thus, the current literature reporting the mechanisms that underlie the beneficial effects of exercise training in the microcirculation distal to epicardial stenosis is reviewed. We also discuss recent studies of therapeutic interventions designed to improve microvascular function and stimulate angiogenesis in clinically relevant animal models of epicardial stenosis and microvascular disease. Finally, microvascular adaptation to removal of epicardial stenosis is considered.

Long Non-coding RNA Aerrie Controls DNA Damage Repair via YBX1 to Maintain Endothelial Cell Function

Aging is accompanied by many physiological changes. These changes can progressively lead to many types of cardiovascular diseases. During this process blood vessels lose their ability to maintain vascular homeostasis, ultimately resulting in hypertension, stroke, or myocardial infarction. Increase in DNA damage is one of the hallmarks of aging and can be repaired by the DNA signaling and repair system. In our study we show that long non-coding RNA Aerrie (linc01013) contributes to the DNA signaling and repair mechanism. Silencing of Aerrie in endothelial cells impairs angiogenesis, migration, and barrier function. Aerrie associates with YBX1 and together they act as important factors in DNA damage signaling and repair. This study identifies Aerrie as a novel factor in genomic stability and as a binding partner of YBX1 in responding to DNA damage.

Effects of aging on coronary flow reserve in patients with no evidence of myocardial perfusion abnormality

Coronary flow reserve (CFR) reflects the functional capacity of microcirculation to adapt to blood demand during increased cardiac work. We tested the hypothesis that aging had impacts on coronary flow velocities and CFR in patients with no evidence of myocardial perfusion abnormality on single photon emission computed tomography (SPECT). Seventy-six patients undergoing transthoracic Doppler echocardiography with no evidence of myocardial perfusion abnormality on SPECT were enrolled in this study. CFR was defined as the ratio of hyperemic to resting peak diastolic coronary flow velocity. Patients were divided into the three groups based on age: 17 patients aged less than 70 years (Group I), 38 patients aged 70-79 years (Group II), and 21 patients aged 80 years or more (Group III). Compared with Group I, CFR was significantly lower in Group II (p < 0.01) and Group III (p < 0.01). Multivariate linear regression analysis showed that female (β = - 0.26, p = 0.03), cigarette smoking (β = - 0.32, p = 0.004), hemoglobin level (β = - 0.40, p = 0.001) and LV mass index (β = 0.24, p = 0.03) were determinants for resting coronary flow velocity. On the other hand, age (β = -0.30, p = 0.008), hemoglobin level (β = -0.47, p < 0.001) and LV mass index (β = 0.24, p = 0.04) were determinants for hyperemic coronary flow velocity. Age was only determinant for CFR (β = -0.48, p < 0.001). Our data suggested that that aging had a decreased effect on hyperemic coronary flow velocity rather than resting coronary flow velocity, and was further associated with impaired CFR in patients with no evidence of myocardial perfusion abnormality.

Ginsenoside Rb1 reduces H2O2‑induced HUVEC dysfunction by stimulating the sirtuin‑1/AMP‑activated protein kinase pathway

Endothelial dysfunction and senescence are closely associated with cardiovascular diseases including atherosclerosis and hypertension. Ginsenoside Rb1 (Rb1), the major active constituent of ginseng, has been investigated intensively because of its anti-obesity and anti-inflammatory effects. In a previous study, hydrogen peroxide (H₂O₂) was applied to induce human umbilical vein endothelial cell (HUVEC) aging. It was demonstrated that Sirtuin-1 (SIRT1) was activated by Rb1 to protect HUVECs from H₂O₂-induced senescence. However, the mechanisms are not fully understood. The present study examined the role of AMP-activated protein kinase (AMPK), an energy sensor of cellular metabolism, in the signaling pathway of SIRT1 during H₂O₂-stimulated HUVEC aging. It was identified that Rb1 restored the H₂O₂-induced reduction of SIRT1 expression, which was consistent with our previous study, together with the activation of AMPK phosphorylation. Using compound C, an AMPK inhibitor, the role of AMPK in the protective effect of Rb1 against H₂O₂-induced HUVEC senescence was examined. It was identified that the induction of phosphorylated AMPK by Rb1 markedly increased endothelial nitric oxide synthase expression and nitric oxide production, and suppressed PAI-1 expression, which were abrogated in HUVECs pretreated with compound C. Further experiments demonstrated that nicotinamide, a SIRT1 inhibitor, downregulated the phosphorylation of AMPK and reduced the protective effects of Rb1 against H₂O₂-induced endothelial aging. Taken together, these results provide new insights into the possible molecular mechanisms by which Rb1 protects against H₂O₂-induced HUVEC senescence via the SIRT1/AMPK pathway.

The hydromechanics in arteriogenesis

Coronary heart diseases are tightly associated with aging. Although current revascularization therapies, such as percutaneous coronary interventions (PCI) and coronary artery bypass graft (CABG), improve the clinical outcomes of patients with coronary diseases, their application and therapeutic effects are limited in elderly patients. Thus, developing novel therapeutic strategies, like prompting collateral development or the process of arteriogenesis, is necessary for the treatment of the elderly with coronary diseases. Arteriogenesis (ie, the vascular remodeling from pre‐existent arterioles to collateral conductance networks) functions as an essential compensation for tissue hypoperfusion caused by artery occlusion or stenosis, and its mechanisms remain to be elucidated. In this review, we will summarize the roles of the major hydromechanical components in laminar conditions in arteriogenesis, and discuss the potential effects of disturbed flow components in non‐laminar conditions.

Redox Regulation of the Microcirculation

The microcirculation maintains tissue homeostasis through local regulation of blood flow and oxygen delivery. Perturbations in microvascular function are characteristic of several diseases and may be early indicators of pathological changes in the cardiovascular system and in parenchymal tissue function. These changes are often mediated by various reactive oxygen species and linked to disruptions in pathways such as vasodilation or angiogenesis. This overview compiles recent advances relating to redox regulation of the microcirculation by adopting both cellular and functional perspectives. Findings from a variety of vascular beds and models are integrated to describe common effects of different reactive species on microvascular function. Gaps in understanding and areas for further research are outlined. © 2020 American Physiological Society. Compr Physiol 10:229-260, 2020.

Changes of the coronary arteries and cardiac microvasculature with aging: Implications for translational research and clinical practice

Aging results in functional and structural changes in the cardiovascular system, translating into a progressive increase of mechanical vessel stiffness, due to a combination of changes in micro-RNA expression patterns, autophagy, arterial calcification, smooth muscle cell migration and proliferation. The two pivotal mechanisms of aging-related endothelial dysfunction are oxidative stress and inflammation, even in the absence of clinical disease. A comprehensive understanding of the aging process is emerging as a primary concern in literature, as vascular aging has recently become a target for prevention and treatment of cardiovascular disease. Change of life-style, diet, antioxidant regimens, anti-inflammatory treatments, senolytic drugs counteract the pro-aging pathways or target senescent cells modulating their detrimental effects. Such therapies aim to reduce the ineluctable burden of age and contrast aging-associated cardiovascular dysfunction. This narrative review intends to summarize the macrovascular and microvascular changes related with aging, as a better understanding of the pathways leading to arterial aging may contribute to design new mechanism-based therapeutic approaches to attenuate the features of vascular senescence and its clinical impact on the cardiovascular system.

Deletion of Robo4 prevents high-fat diet-induced adipose artery and systemic metabolic dysfunction

OBJECTIVE

Accumulating evidence suggests the vascular endothelium plays a fundamental role in the pathophysiology of obesity by regulating the functional status of white adipose and systemic metabolism. Robo4 is expressed specifically in endothelial cells and increases vascular stability and inhibits angiogenesis. We sought to determine the role of Robo4 in modulating cardiometabolic function in response to high-fat feeding.

METHODS

We examined exercise capacity, glucose tolerance, and white adipose tissue artery gene expression, endothelium-dependent dilation (EDD), and angiogenesis in wild type and Robo4 knockout (KO) mice fed normal chow (NC) or a high-fat diet (HFD).

RESULTS

We found Robo4 deletion enhances exercise capacity in NC-fed mice and HFD markedly increased the expression of the Robo4 ligand, Slit2, in white adipose tissue. Deletion of Robo4 increased angiogenesis in white adipose tissue and protected against HFD-induced impairments in white adipose artery vasodilation and glucose intolerance.

CONCLUSIONS

We demonstrate a novel functional role for Robo4 in endothelial cell function and metabolic homeostasis in white adipose tissue, with Robo4 deletion protecting against endothelial and metabolic dysfunction associated with a HFD. Our findings suggest that Robo4-dependent signaling pathways may be a novel target in anti-obesity therapy.

Voluntary wheel running prevents salt-induced endothelial dysfunction: role of oxidative stress

Diets high in salt can lead to endothelial dysfunction, a nontraditional risk factor for cardiovascular disease (CVD). Exercise is known to reduce CVD risk; however, it remains unknown whether chronic physical activity can attenuate salt-induced endothelial dysfunction independent of blood pressure (BP) and whether these changes are due to an upregulation in endogenous antioxidants. Eight-week-old Sprague-Dawley rats were fed either a normal (NS; 0.49%)- or a high (HS; 4.0%)-salt diet and further divided into voluntary wheel running (NS-VWR, HS-VWR) and sedentary (NS, HS) groups for 6 wk. BP was measured weekly and remained unchanged within groups ( P = 0.373). Endothelium-dependent relaxation (EDR) was impaired in the femoral artery of HS compared with NS (38.6 ± 4.0% vs. 65.0 ± 3.6%; P = 0.013) animals, whereas it was not different between NS and HS-VWR (73.4 ± 6.4%; P = 0.273) animals. Incubation with the antioxidants TEMPOL ( P = 0.024) and apocynin ( P = 0.013) improved EDR in HS animals, indicating a role for reactive oxygen species (ROS). Wheel running upregulated the antioxidant superoxide dismutase-2 (SOD-2) ( P = 0.011) under HS conditions and lowered NOX4 and Gp91-phox, two subunits of NADPH oxidase. Wheel running elevated phosphorylated endothelial nitric oxide synthase (eNOS) ( P = 0.014) in HS-fed rats, demonstrating a role for physical activity and eNOS activity under HS conditions. Finally, there was a reduction in EDR ( P = 0.038) when femoral arteries from NS-VWR animals were incubated with TEMPOL or apocynin, suggesting there may be a critical level of ROS needed to maintain endothelial function. In summary, physical activity protected HS-fed rats from reductions in endothelial function, likely through increased SOD-2 levels and reduced oxidative stress. NEW & NOTEWORTHY Our data suggest that voluntary wheel running can prevent impairments in endothelium-dependent relaxation in the femoral artery of rats fed a high-salt diet. This appears to be independent of blood pressure and mediated through a decrease in expression of NADPH oxidases as a result of physical activity. These data suggest that increased chronic physical activity can protect the vasculature from a diet high in salt, likely through a reduction in oxidative stress.

Current themes in myocardial and coronary vascular aging

Advancing age will affect every individual and its impact on cardiac health deserves significant attention. The age-related physiological changes occurring in the coronary vasculature, myocardium, and valves set the stage upon which cardiovascular disease can escalate in the elderly population. The overall focus of this review is to highlight new and noteworthy studies and to incorporate reviews related to cardiac senescence in the context of the current state of the field. Lastly, future directions in the field of cardiac aging and the development of novel therapeutics to treat pathophysiological conditions typically associated with advancing age will be discussed.

Age-associated pro-inflammatory adaptations of the mouse thoracic aorta

Arterial ageing may be associated with a reduction in vasodilation due to increased reactive oxygen species (ROS) production, whereas endothelial cell activation induces procoagulant changes. However, little is known on the effect of ageing on expression of anticoagulant endothelial markers such as endothelial protein C receptor (EPCR). To study age-associated alterations in smooth muscle cell (SMC) and endothelial cell (EC) structure and function, the aorta was isolated from 10-week-and 12– and 24-month-old C57BL/6J mice and analysed for its expression of genes involved in senescence, oxidative stress production, coagulation and matrix remodelling. In addition, vasorelaxation experiments were performed using 10-week-and 24-month-old thoracic aortic ring segments in organ chamber baths. The media thickness of the thoracic aorta progressively increased with age, associated with hypertrophy of vascular SMCs. Basal nitric oxide production and sensitivity to acetylcholine-mediated vasodilation in thoracic aorta rings was reduced with age, whereas no significant differences in ROS production could be demonstrated. Gene expression of tissue factor, EPCR and von Willebrand factor was not affected by ageing of the aorta, whereas that of thrombomodulin was mildly reduced and that of xanthine dehydrogenase, NADPH oxidase 4, tumour necrosis factor-α and vascular cell adhesion molecule-1 significantly enhanced. In conclusion, a reduction in endothelial cell-mediated vasodilation in aged thoracic aortas of C57BL/6J mice was accompanied by a shift towards a pro-inflammatory state of the endothelium.

Mechanical, hormonal and metabolic influences on blood vessels, blood flow and bone

Bone tissue is highly vascularized due to the various roles bone blood vessels play in bone and bone marrow function. For example, the vascular system is critical for bone development, maintenance and repair and provides O₂, nutrients, waste elimination, systemic hormones and precursor cells for bone remodeling. Further, bone blood vessels serve as egress and ingress routes for blood and immune cells to and from the bone marrow. It is becoming increasingly clear that the vascular and skeletal systems are intimately linked in metabolic regulation and physiological and pathological processes. This review examines how agents such as mechanical loading, parathyroid hormone, estrogen, vitamin D and calcitonin, all considered anabolic for bone, have tremendous impacts on the bone vasculature. In fact, these agents influence bone blood vessels prior to influencing bone. Further, data reveal strong associations between vasodilator capacity of bone blood vessels and trabecular bone volume, and poor associations between estrogen status and uterine mass and trabecular bone volume. Additionally, this review highlights the importance of the bone microcirculation, particularly the vascular endothelium and NO-mediated signaling, in the regulation of bone blood flow, bone interstitial fluid flow and pressure and the paracrine signaling of bone cells. Finally, the vascular endothelium as a mediator of bone health and disease is considered.

Thrombospondin-1, Free Radicals, and the Coronary Microcirculation: The Aging Conundrum

SIGNIFICANCE

Successful matching of cardiac metabolism to perfusion is accomplished primarily through vasodilation of the coronary resistance arterioles, but the mechanism that achieves this effect changes significantly as aging progresses and involves the contribution of reactive oxygen species (ROS). Recent Advances: A matricellular protein, thrombospondin-1 (Thbs-1), has been shown to be a prolific contributor to the production and modulation of ROS in large conductance vessels and in the peripheral circulation. Recently, the presence of physiologically relevant circulating Thbs-1 levels was proven to also disrupt vasodilation to nitric oxide (NO) in coronary arterioles from aged animals, negatively impacting coronary blood flow reserve.

CRITICAL ISSUES

This review seeks to reconcile how ROS can be successfully utilized as a substrate to mediate vasoreactivity in the coronary microcirculation as "normal" aging progresses, but will also examine how Thbs-1-induced ROS production leads to dysfunctional perfusion and eventual ischemia and why this is more of a concern in advancing age.

FUTURE DIRECTIONS

Current therapies that may effectively disrupt Thbs-1 and its receptor CD47 in the vascular wall and areas for future exploration will be discussed. Antioxid. Redox Signal. 27, 785-801.

Effects of age and exercise training on coronary microvascular smooth muscle phenotype and function

Coronary microvascular function and blood flow responses during acute exercise are impaired in the aged heart but can be restored by exercise training. Coronary microvascular resistance is directly dependent on vascular smooth muscle function in coronary resistance arterioles; therefore, we hypothesized that age impairs contractile function and alters the phenotype of vascular smooth muscle in coronary arterioles. We further hypothesized that exercise training restores contractile function and reverses age-induced phenotypic alterations of arteriolar smooth muscle. Young and old Fischer 344 rats underwent 10 wk of treadmill exercise training or remained sedentary. At the end of training or cage confinement, contractile responses, vascular smooth muscle proliferation, and expression of contractile proteins were assessed in isolated coronary arterioles. Both receptor- and non-receptor-mediated contractile function were impaired in coronary arterioles from aged rats. Vascular smooth muscle shifted from a differentiated, contractile phenotype to a secretory phenotype with associated proliferation of smooth muscle in the arteriolar wall. Expression of smooth muscle myosin heavy chain 1 (SM1) was decreased in arterioles from aged rats, whereas expression of phospho-histone H3 and of the synthetic protein ribosomal protein S6 (rpS6) were increased. Exercise training improved contractile responses, reduced smooth muscle proliferation and expression of rpS6, and increased expression of SM1 in arterioles from old rats. Thus age-induced contractile dysfunction of coronary arterioles and emergence of a secretory smooth muscle phenotype may contribute to impaired coronary blood flow responses, but arteriolar contractile responsiveness and a younger smooth muscle phenotype can be restored with late-life exercise training. NEW & NOTEWORTHY Aging impairs contractile function of coronary arterioles and induces a shift of the vascular smooth muscle toward a proliferative, noncontractile phenotype. Late-life exercise training reverses contractile dysfunction of coronary arterioles and restores a young phenotype to the vascular smooth muscle.

Exercise training reverses age-induced diastolic dysfunction and restores coronary microvascular function

KEY POINTS

In a rat model of ageing that is free of atherosclerosis or hypertension, E/A, a diagnostic measure of diastolic filling, decreases, and isovolumic relaxation time increases, indicating that both active and passive ventricular relaxation are impaired with advancing age. Resting coronary blood flow and coronary functional hyperaemia are reduced with age, and endothelium-dependent vasodilatation declines with age in coronary resistance arterioles. Exercise training reverses age-induced declines in diastolic and coronary microvascular function. Thus, microvascular dysfunction and inadequate coronary perfusion are likely mechanisms of diastolic dysfunction in aged rats. Exercise training, initiated at an advanced age, reverses age-related diastolic and microvascular dysfunction; these data suggest that late-life exercise training can be implemented to improve coronary perfusion and diastolic function in the elderly.

ABSTRACT

The risk for diastolic dysfunction increases with advancing age. Regular exercise training ameliorates age-related diastolic dysfunction; however, the underlying mechanisms have not been identified. We investigated whether (1) microvascular dysfunction contributes to the development of age-related diastolic dysfunction, and (2) initiation of late-life exercise training reverses age-related diastolic and microvascular dysfunction. Young and old rats underwent 10 weeks of exercise training or remained as sedentary, cage-controls. Isovolumic relaxation time (IVRT), early diastolic filling (E/A), myocardial performance index (MPI) and aortic stiffness (pulse wave velocity; PWV) were evaluated before and after exercise training or cage confinement. Coronary blood flow and vasodilatory responses of coronary arterioles were evaluated in all groups at the end of training. In aged sedentary rats, compared to young sedentary rats, a 42% increase in IVRT, a 64% decrease in E/A, and increased aortic stiffness (PWV: 6.36 ± 0.47 vs.4.89 ± 0.41, OSED vs. YSED, P < 0.05) was accompanied by impaired coronary blood flow at rest and during exercise. Endothelium-dependent vasodilatation was impaired in coronary arterioles from aged rats (maximal relaxation to bradykinin: 56.4 ± 5.1% vs. 75.3 ± 5.2%, OSED vs. YSED, P < 0.05). After exercise training, IVRT, a measure of active ventricular relaxation, did not differ between old and young rats. In old rats, exercise training reversed the reduction in E/A, reduced aortic stiffness, and eliminated impairment of coronary blood flow responses and endothelium-dependent vasodilatation. Thus, age-related diastolic and microvascular dysfunction are reversed by late-life exercise training. The restorative effect of exercise training on coronary microvascular function may result from improved endothelial function.

NO-mediated anticontractile effect of the endothelium is abolished in coronary arteries of adult rats with antenatal/early postnatal hypothyroidism

INTRODUCTION

Thyroid hormones are essential for proper development of many systems and organs, including circulatory system. Thyroid deficiency during pregnancy may affect the cardiovascular function in children early on and later in adulthood. However, long-term effects of early thyroid deficiency are poorly understood. We hypothesized that antenatal/early postnatal hypothyroidism will influence anticontractile effect of NO in coronary arteries of adult rats.

DESIGN AND METHODS

To model antenatal/early postnatal hypothyroidism dams were treated with 6-propyl-2-thiouracil (PTU) in drinking water (0.0007%, w/v) from the first day of pregnancy till 2 weeks after delivery. Control females were supplied with pure water. Their male offspring was grown up till the age of 10-12 weeks. Systolic blood pressure was measured using tail cuff method. Septal coronary arteries were isolated and studied in wire myograph. Blood serum thyroid hormones concentrations (ELISA) and NO metabolites level (Griess method) were evaluated.

RESULTS

At the age of 10-12 weeks thyroid hormones, TSH concentrations, NO metabolites and systolic blood pressure level didn't differ between groups. Arterial responses to acetylcholine and exogenous NO-donor DEA/NO were similar in control and PTU groups. Along with that, in control rats endothelium denudation strongly potentiated basal tone of arteries and their contractile responses to thromboxane A2 receptor agonist U46619. The effects of endothelium denudation were absent in PTU rats indicating that anticontractile effect of endothelium is abolished in their arteries. Further, NO-synthase inhibitor L-NNA (100 μM) caused significant elevation of basal tone and increased U46619-induced contraction of endothelium-intact arteries only in control rats, while had no effect in PTU group.

CONCLUSIONS

Our data demonstrate that NO-mediated anticontractile effect of endothelium is eliminated in coronary arteries of adult rats, which suffered from antenatal/early postnatal hypothyroidism. Therefore, maternal thyroid hormones deficiency may have detrimental consequences in adult offspring including coronary circulation pathologies, despite normal blood levels of thyroid hormones.

Nitric oxide and the cardiovascular system

Nitric oxide (NO) generated by endothelial cells to relax vascular smooth muscle is one of the most intensely studied molecules in the past 25 years. Much of what is known about NO regulation of NO is based on blockade of its generation and analysis of changes in vascular regulation. This approach has been useful to demonstrate the importance of NO in large scale forms of regulation but provides less information on the nuances of NO regulation. However, there is a growing body of studies on multiple types of in vivo measurement of NO in normal and pathological conditions. This discussion will focus on in vivo studies and how they are reshaping the understanding of NO's role in vascular resistance regulation and the pathologies of hypertension and diabetes mellitus. The role of microelectrode measurements in the measurement of [NO] will be considered because much of the controversy about what NO does and at what concentration depends upon the measurement methodology. For those studies where the technology has been tested and found to be well founded, the concept evolving is that the stresses imposed on the vasculature in the form of flow-mediated stimulation, chemicals within the tissue, and oxygen tension can cause rapid and large changes in the NO concentration to affect vascular regulation. All these functions are compromised in both animal and human forms of hypertension and diabetes mellitus due to altered regulation of endothelial cells and formation of oxidants that both damage endothelial cells and change the regulation of endothelial nitric oxide synthase.

Cellular and molecular biology of aging endothelial cells

Cardiovascular disease (CVD) is the leading cause of death in the United States and aging is a major risk factor for CVD development. One of the major age-related arterial phenotypes thought to be responsible for the development of CVD in older adults is endothelial dysfunction. Endothelial function is modulated by traditional CVD risk factors in young adults, but advancing age is independently associated with the development of vascular endothelial dysfunction. This endothelial dysfunction results from a reduction in nitric oxide bioavailability downstream of endothelial oxidative stress and inflammation that can be further modulated by traditional CVD risk factors in older adults. Greater endothelial oxidative stress with aging is a result of augmented production from the intracellular enzymes NADPH oxidase and uncoupled eNOS, as well as from mitochondrial respiration in the absence of appropriate increases in antioxidant defenses as regulated by relevant transcription factors, such as FOXO. Interestingly, it appears that NFkB, a critical inflammatory transcription factor, is sensitive to this age-related endothelial redox change and its activation induces transcription of pro-inflammatory cytokines that can further suppress endothelial function, thus creating a vicious feed-forward cycle. This review will discuss the two macro-mechanistic processes, oxidative stress and inflammation, that contribute to endothelial dysfunction with advancing age as well as the cellular and molecular events that lead to the vicious cycle of inflammation and oxidative stress in the aged endothelium. Other potential mediators of this pro-inflammatory endothelial phenotype are increases in immune or senescent cells in the vasculature. Of note, genomic instability, telomere dysfunction or DNA damage has been shown to trigger cell senescence via the p53/p21 pathway and result in increased inflammatory signaling in arteries from older adults. This review will discuss the current state of knowledge regarding the emerging concepts of senescence and genomic instability as mechanisms underlying oxidative stress and inflammation in the aged endothelium. Lastly, energy sensitive/stress resistance pathways (SIRT-1, AMPK, mTOR) are altered in endothelial cells and/or arteries with aging and these pathways may modulate endothelial function via key oxidative stress and inflammation-related transcription factors. This review will also discuss what is known about the role of "energy sensing" longevity pathways in modulating endothelial function with advancing age. With the growing population of older adults, elucidating the cellular and molecular mechanisms of endothelial dysfunction with age is critical to establishing appropriate and measured strategies to utilize pharmacological and lifestyle interventions aimed at alleviating CVD risk. This article is part of a Special Issue entitled "SI: CV Aging".

Vascular TRP channels: performing under pressure and going with the flow

Endothelial cells and smooth muscle cells of resistance arteries mediate opposing responses to mechanical forces acting on the vasculature, promoting dilation in response to flow and constriction in response to pressure, respectively. In this review, we explore the role of TRP channels, particularly endothelial TRPV4 and smooth muscle TRPC6 and TRPM4 channels, in vascular mechanosensing circuits, placing their putative mechanosensitivity in context with other proposed upstream and downstream signaling pathways.

Systemically delivered adipose stromal vascular fraction cells disseminate to peripheral artery walls and reduce vasomotor tone through a CD11b+ cell-dependent mechanism

Vasoactivity, an important aspect of tissue healing, is often compromised in disease and tissue injury. Dysfunction in the smaller vasoactive arteries is most impactful, given the role of these vessels in controlling downstream tissue perfusion. The adipose stromal vascular fraction (SVF) is a mix of homeostatic cells shown to promote tissue healing. Our objective was to test the hypothesis that autologous SVF cells therapeutically modulate peripheral artery vasoactivity in syngeneic mouse models of small artery function. Analysis of vasoactivity of saphenous arteries isolated from normal mice 1 week after intravenous injection of freshly isolated SVF cells revealed that pressure-dependent artery vasomotor tone was decreased by the SVF cell isolate, but not one depleted of CD11b(+) cells. Scavenging hydrogen peroxide in the vessel wall abrogated the artery relaxation promoted by the SVF cell isolate. Consistent with a CD11b(+) cell being the relevant cell type, SVF-derived F4/80-positive macrophages were present within the adventitia of the artery wall coincident with vasorelaxation. In a model of artery inflammation mimicking a common disease condition inducing vasoactive dysfunction, the SVF cells potentiated relaxation of saphenous arteries without structurally remodeling the artery via a CD11b(+) cell-dependent manner. Our findings demonstrate that freshly isolated, adipose SVF cells promote vasomotor relaxation in vasoactive arteries via a hydrogen peroxide-dependent mechanism that required CD11b(+) cells (most likely macrophages). Given the significant impact of small artery dysfunction in disease, we predict that the intravenous delivery of this therapeutic cell preparation would significantly improve tissue perfusion, particularly in diseases with diffuse vascular involvement.

Structural remodeling of coronary resistance arteries: effects of age and exercise training

Age is known to induce remodeling and stiffening of large-conduit arteries; however, little is known of the effects of age on remodeling and mechanical properties of coronary resistance arteries. We employed a rat model of aging to investigate whether 1) age increases wall thickness and stiffness of coronary resistance arteries, and 2) exercise training reverses putative age-induced increases in wall thickness and stiffness of coronary resistance arteries. Young (4 mo) and old (21 mo) Fischer 344 rats remained sedentary or underwent 10 wk of treadmill exercise training. Coronary resistance arteries were isolated for determination of wall-to-lumen ratio, effective elastic modulus, and active and passive responses to changes in intraluminal pressure. Elastin and collagen content of the vascular wall were assessed histologically. Wall-to-lumen ratio increased with age, but this increase was reversed by exercise training. In contrast, age reduced stiffness, and exercise training increased stiffness in coronary resistance arteries from old rats. Myogenic responsiveness was reduced with age and restored by exercise training. Collagen-to-elastin ratio (C/E) of the wall did not change with age and was reduced with exercise training in arteries from old rats. Thus age induces hypertrophic remodeling of the vessel wall and reduces the stiffness and myogenic function of coronary resistance arteries. Exercise training reduces wall-to-lumen ratio, increases wall stiffness, and restores myogenic function in aged coronary resistance arteries. The restorative effect of exercise training on myogenic function of coronary resistance arteries may be due to both changes in vascular smooth muscle phenotype and expression of extracellular matrix proteins.

Nox2 and p47(phox) modulate compensatory growth of primary collateral arteries

The role of NADPH oxidase (Nox) in both the promotion and impairment of compensatory collateral growth remains controversial because the specific Nox and reactive oxygen species involved are unclear. The aim of this study was to identify the primary Nox and reactive oxygen species associated with early stage compensatory collateral growth in young, healthy animals. Ligation of the feed arteries that form primary collateral pathways in rat mesentery and mouse hindlimb was used to assess the role of Nox during collateral growth. Changes in mesenteric collateral artery Nox mRNA expression determined by real-time PCR at 1, 3, and 7 days relative to same-animal control arteries suggested a role for Nox subunits Nox2 and p47(phox). Administration of apocynin or Nox2ds-tat suppressed collateral growth in both rat and mouse models, suggesting the Nox2/p47(phox) interaction was involved. Functional significance of p47(phox) expression was assessed by evaluation of collateral growth in rats administered p47(phox) small interfering RNA and in p47(phox-/-) mice. Diameter measurements of collateral mesenteric and gracilis arteries at 7 and 14 days, respectively, indicated no significant collateral growth compared with control rats or C57BL/6 mice. Chronic polyethylene glycol-conjugated catalase administration significantly suppressed collateral development in rats and mice, implying a requirement for H2O2. Taken together, these results suggest that Nox2, modulated at least in part by p47(phox), mediates early stage compensatory collateral development via a process dependent upon peroxide generation. These results have important implications for the use of antioxidants and the development of therapies for peripheral arterial disease.

Aging impairs electrical conduction along endothelium of resistance arteries through enhanced Ca2+-activated K+ channel activation

OBJECTIVE

Intercellular conduction of electrical signals underlies spreading vasodilation of resistance arteries. Small- and intermediate-conductance Ca(2+)-activated K(+) channels of endothelial cells serve a dual function by initiating hyperpolarization and modulating electrical conduction. We tested the hypothesis that regulation of electrical signaling by small- and intermediate-conductance Ca(2+)-activated K(+) channels is altered with advancing age.

APPROACH AND RESULTS

Intact endothelial tubes (60 µm wide; 1-3 mm long) were freshly isolated from male C57BL/6 mouse (Young: 4-6 months; Intermediate: 12-14 months; Old: 24-26 months) superior epigastric arteries. Using dual intracellular microelectrodes, current was injected (± 0.1-3 nA) at site 1 while recording membrane potential (Vm) at site 2 (separation distance: 50-2000 µm). Across age groups, greatest differences were observed between Young and Old. Resting Vm in Old (-38 ± 1 mV) was more negative (P<0.05) than Young (-30 ± 1 mV). Maximal hyperpolarization to both direct (NS309) and indirect (acetylcholine) activation of small- and intermediate-conductance Ca(2+)-activated K(+) channels was sustained (ΔVm ≈-40 mV) with age. The length constant (λ) for electrical conduction was reduced (P<0.05) from 1630 ± 80 µm (Young) to 1320 ± 80 µm (Old). Inhibiting small- and intermediate-conductance Ca(2+)-activated K(+) channels with apamin+charybdotoxin or scavenging hydrogen peroxide (H2O2) with catalase improved electrical conduction (P<0.05) in Old. Exogenous H2O2 (200 µmol/L) in Young evoked hyperpolarization and impaired electrical conduction; these effects were blocked by apamin+charybdotoxin.

CONCLUSIONS

Enhanced current loss through Ca2+-activated K+ channel activation impairs electrical conduction along the endothelium of resistance arteries with aging. Attenuating the spatial domain of electrical signaling will restrict the spread of vasodilation and thereby contribute to blood flow limitations associated with advanced age.

Network remodeling of intramural coronary resistance arteries in the aged rat: a statistical analysis of geometry

AIMS

To identify the geometrical alterations in the age-remodeled rat coronary artery network and to develop a useful technique to analyze network properties in the rat heart.

METHODS AND RESULTS

We analyzed the networks of the left anterior descendent coronary arteries on in situ perfused hearts of young (3 months) and old (18 months) male rats. All segments and branching over >80 μm diameter were analyzed using 50 μm long cylindrical ring units of the networks. Arterial widening and paucity, increased tortuosity were typical features in the old network. In addition, axis angles deviated more from the mother branches in the old, whereas the diameters of daughter branches fit the Murray law in both groups. The detected changes in the old network resulted in a longer blood flow route for the same direct distance.

CONCLUSION

We developed a useful method to investigate arterial network property changes in the rat heart. Ageing resulted in longer, more tortuous flow route in the LAD network that might be hemodynamically disadvantageous.

Effects of short-term dietary nitrate supplementation on blood pressure, O2 uptake kinetics, and muscle and cognitive function in older adults

Dietary nitrate (NO3−) supplementation has been shown to reduce resting blood pressure and alter the physiological response to exercise in young adults. We investigated whether these effects might also be evident in older adults. In a double-blind, randomized, crossover study, 12 healthy, older (60–70 yr) adults supplemented their diet for 3 days with either nitrate-rich concentrated beetroot juice (BR; 2 × 70 ml/day, ∼9.6 mmol/day NO3−) or a nitrate-depleted beetroot juice placebo (PL; 2 × 70 ml/day, ∼0.01 mmol/day NO3−). Before and after the intervention periods, resting blood pressure and plasma [nitrite] were measured, and subjects completed a battery of physiological and cognitive tests. Nitrate supplementation significantly increased plasma [nitrite] and reduced resting systolic (BR: 115 ± 9 vs. PL: 120 ± 6 mmHg; P < 0.05) and diastolic (BR: 70 ± 5 vs. PL: 73 ± 5 mmHg; P < 0.05) blood pressure. Nitrate supplementation resulted in a speeding of the V̇o2 mean response time (BR: 25 ± 7 vs. PL: 28 ± 7 s; P < 0.05) in the transition from standing rest to treadmill walking, although in contrast to our hypothesis, the O2 cost of exercise remained unchanged. Functional capacity (6-min walk test), the muscle metabolic response to low-intensity exercise, brain metabolite concentrations, and cognitive function were also not altered. Dietary nitrate supplementation reduced resting blood pressure and improved V̇o2 kinetics during treadmill walking in healthy older adults but did not improve walking or cognitive performance. These results may have implications for the enhancement of cardiovascular health in older age.

Age and exercise training alter signaling through reactive oxygen species in the endothelium of skeletal muscle arterioles

Exercise training ameliorates age-related impairments in endothelium-dependent vasodilation in skeletal muscle arterioles. Additionally, exercise training is associated with increased superoxide production. The purpose of this study was to determine the role of superoxide and superoxide-derived reactive oxygen species (ROS) signaling in mediating endothelium-dependent vasodilation of soleus muscle resistance arterioles from young and old, sedentary and exercise-trained rats. Young (3 mo) and old (22 mo) male rats were either exercise trained or remained sedentary for 10 wk. To determine the impact of ROS signaling on endothelium-dependent vasodilation, responses to acetylcholine were studied under control conditions and during the scavenging of superoxide and/or hydrogen peroxide. To determine the impact of NADPH oxidase-derived ROS, endothelium-dependent vasodilation was determined following NADPH oxidase inhibition. Reactivity to superoxide and hydrogen peroxide was also determined. Tempol, a scavenger of superoxide, and inhibitors of NADPH oxidase reduced endothelium-dependent vasodilation in all groups. Similarly, treatment with catalase and simultaneous treatment with tempol and catalase reduced endothelium-dependent vasodilation in all groups. Decomposition of peroxynitrite also reduced endothelium-dependent vasodilation. Aging had no effect on arteriolar protein content of SOD-1, catalase, or glutathione peroxidase-1; however, exercise training increased protein content of SOD-1 in young and old rats, catalase in young rats, and glutathione peroxidase-1 in old rats. These data indicate that ROS signaling is necessary for endothelium-dependent vasodilation in soleus muscle arterioles, and that exercise training-induced enhancement of endothelial function occurs, in part, through an increase in ROS signaling.

Mechanical ventilation reduces rat diaphragm blood flow and impairs oxygen delivery and uptake

OBJECTIVES

Although mechanical ventilation is a life-saving intervention in patients suffering from respiratory failure, prolonged mechanical ventilation is often associated with numerous complications including problematic weaning. In contracting skeletal muscle, inadequate oxygen supply can limit oxidative phosphorylation resulting in muscular fatigue. However, whether prolonged mechanical ventilation results in decreased diaphragmatic blood flow and induces an oxygen supply-demand imbalance in the diaphragm remains unknown.

DESIGN

We tested the hypothesis that prolonged controlled mechanical ventilation results in a time-dependent reduction in rat diaphragmatic blood flow and microvascular PO2 and that prolonged mechanical ventilation would diminish the diaphragm's ability to increase blood flow in response to muscular contractions.

MEASUREMENTS AND MAIN RESULTS

Compared to 30 mins of mechanical ventilation, 6 hrs of mechanical ventilation resulted in a 75% reduction in diaphragm blood flow (via radiolabeled microspheres), which did not occur in the intercostal muscle or high-oxidative hindlimb muscle (e.g., soleus). There was also a time-dependent decline in diaphragm microvascular PO2 (via phosphorescence quenching). Further, contrary to 30 mins of mechanical ventilation, 6 hrs of mechanical ventilation significantly compromised the diaphragm's ability to increase blood flow during electrically-induced contractions, which resulted in a ~80% reduction in diaphragm oxygen uptake. In contrast, 6 hrs of spontaneous breathing in anesthetized animals did not alter diaphragm blood flow or the ability to augment flow during electrically-induced contractions.

CONCLUSIONS

These new and important findings reveal that prolonged mechanical ventilation results in a time-dependent decrease in the ability of the diaphragm to augment blood flow to match oxygen demand in response to contractile activity and could be a key contributing factor to difficult weaning. Although additional experiments are required to confirm, it is tempting to speculate that this ventilator-induced decline in diaphragmatic oxygenation could promote a hypoxia-induced generation of reactive oxygen species in diaphragm muscle fibers and contribute to ventilator-induced diaphragmatic atrophy and contractile dysfunction.

Estrogen and the cardiovascular system

Estrogen is a potent steroid with pleiotropic effects, which have yet to be fully elucidated. Estrogen has both nuclear and non-nuclear effects. The rapid response to estrogen, which involves a membrane associated estrogen receptor(ER) and is protective, involves signaling through PI3K, Akt, and ERK 1/2. The nuclear response is much slower, as the ER-estrogen complex moves to the nucleus, where it functions as a transcription factor, both activating and repressing gene expression. Several different ERs regulate the specificity of response to estrogen, and appear to have specific effects in cardiac remodeling and the response to injury. However, much remains to be understood about the selectivity of these receptors and their specific effects on gene expression. Basic studies have demonstrated that estrogen treatment prevents apoptosis and necrosis of cardiac and endothelial cells. Estrogen also attenuates pathologic cardiac hypertrophy. Estrogen may have great benefit in aging as an anti-inflammatory agent. However, clinical investigations of estrogen have had mixed results, and not shown the clear-cut benefit of more basic investigations. This can be explained in part by differences in study design: in basic studies estrogen treatment was used immediately or shortly after ovariectomy, while in some key clinical trials, estrogen was given years after menopause. Further basic research into the underlying molecular mechanisms of estrogen's actions is essential to provide a better comprehension of the many properties of this powerful hormone.

The intersection between aging and cardiovascular disease

The average lifespan of humans is increasing, and with it the percentage of people entering the 65 and older age group is growing rapidly and will continue to do so in the next 20 years. Within this age group, cardiovascular disease will remain the leading cause of death, and the cost associated with treatment will continue to increase. Aging is an inevitable part of life and unfortunately poses the largest risk factor for cardiovascular disease. Although numerous studies in the cardiovascular field have considered both young and aged humans, there are still many unanswered questions as to how the genetic pathways that regulate aging in model organisms influence cardiovascular aging. Likewise, in the molecular biology of aging field, few studies fully assess the role of these aging pathways in cardiovascular health. Fortunately, this gap is beginning to close, and these two fields are merging together. We provide an overview of some of the key genes involved in regulating lifespan and health span, including sirtuins, AMP-activated protein kinase, mammalian target of rapamycin, and insulin-like growth factor 1 and their roles regulating cardiovascular health. We then discuss a series of review articles that will appear in succession and provide a more comprehensive analysis of studies carried out linking genes of aging and cardiovascular health, and perspectives of future directions of these two intimately linked fields.

Redox balance in the aging microcirculation: new friends, new foes, and new clinical directions

Cardiovascular aging is associated with a decline in the function of the vascular endothelium. Considerable evidence indicates that age-induced impairment of endothelium-dependent vasodilation results from a reduction in the availability of nitric oxide (NO(•) ). NO(•) can be scavenged by reactive oxygen species (ROS), in particular by superoxide radical (O(2) (•-) ), and age-related increases in ROS have been demonstrated to contribute to reduced endothelium-dependent vasodilation in numerous large artery preparations. In contrast, emerging data suggest that ROS may play a compensatory role in endothelial function of the aging microvasculature. The primary goal of this review is to discuss reports in the literature which indicate that ROS function as important signaling molecules in the aging microvasculature. Emphasis is placed upon discussion of the emerging roles of hydrogen peroxide (H(2) O(2) ) and peroxynitrite (ONOO(•-) ) in the aging microcirculation. Overall, existing data in animal models suggest that maintenance in the balance of ROS is critical to successful microvascular aging. The limited work that has been performed to investigate the role of ROS in human microvascular aging is also discussed, and the need for future investigations of ROS signaling in older humans is considered.

Hydrogen peroxide enhances vasodilatation by increasing dimerization of cGMP-dependent protein kinase type Iα

BACKGROUND

cGMP-dependent protein kinase type I (PKG I) plays a key role in vasodilatation caused by cGMP-elevating agents. It is a homodimer in mammalian cells, existing as 2 isoforms, Iα and Iβ. The aim of the present study was both to determine whether PKG I dimerization and activity are modulated by hydrogen peroxide (H(2)O(2)) and its influence on vasodilatation.

METHODS AND RESULTS

The dimers and monomers of total PKG I and PKG Iβ were analyzed by Western blotting. PKG I activity was assayed by measuring the incorporation of (32)P into BPDEtide. Changes in vessels tension were determined by organ chamber technique. In isolated porcine coronary arteries, H(2)O(2) increased the dimers of total PKG I in a concentration-dependent manner, but had no effect on dimerization of PKG Iβ. The dimerization of PKG I caused by H(2)O(2) was prevented by catalase but not by deferoxamine and tiron. H(2)O(2) promoted the translocation of PKG I from cytoplasm to membrane. H(2)O(2) enhanced the activity of PKG I and relaxations of porcine coronary arteries to the nitric oxide donor and 8-Br-cGMP. Inhibition of catalase under in vivo conditions significantly decreased rat mean arterial pressure, which was associated with increased dimerization of PKG I.

CONCLUSIONS

The present study suggests that H(2)O(2) may enhance the activity of PKG Iα-and PKG I-dependent vasodilatation via increased dimerization of the enzyme.

Effect of exercise training on nitric oxide and superoxide/H₂O₂ signaling pathways in collateral-dependent porcine coronary arterioles

Endothelial nitric oxide (NO) synthase (NOS) has been shown to contribute to enhanced vascular function after exercise training. Recent studies have revealed that relatively low concentrations of reactive oxygen species can contribute to endothelium-dependent vasodilation under physiological conditions. We tested the hypothesis that exercise training enhances endothelial function via endothelium-derived vasodilators, NO and superoxide/H(2)O(2), in the underlying setting of chronic coronary artery occlusion. An ameroid constrictor was placed around the proximal left circumflex coronary artery to induce gradual occlusion in Yucatan miniature swine. At 8 wk postoperatively, pigs were randomly assigned to sedentary (pen-confined) or exercise-training (treadmill-run: 5 days/wk for 14 wk) regimens. Exercise training significantly enhanced concentration-dependent, bradykinin-mediated dilation in cannulated collateral-dependent arterioles (∼130 μm diameter) compared with sedentary pigs. NOS inhibition reversed training-enhanced dilation at low bradykinin concentrations in collateral-dependent arterioles, although increased dilation persisted at higher bradykinin concentrations. Total and phosphorylated (Ser(1179)) endothelial NOS protein levels were significantly increased in arterioles from collateral-dependent compared with the nonoccluded region, independent of exercise. The H(2)O(2) scavenger polyethylene glycol-catalase abolished the training-enhanced bradykinin-mediated dilation in collateral-dependent arterioles; similar results were observed with the SOD inhibitor diethyldithiocarbamate. Fluorescence measures of bradykinin-stimulated H(2)O(2) levels were significantly increased by exercise training, independent of occlusion. The NADPH inhibitor apocynin significantly attenuated bradykinin-mediated dilation in arterioles of exercise-trained, but not sedentary, pigs and was associated with significantly increased protein levels of the NADPH subunit p67phox. These data provide evidence that, in addition to NO, the superoxide/H(2)O(2) signaling pathway significantly contributes to exercise training-enhanced endothelium-mediated dilation in collateral-dependent coronary arterioles.

Changes in eNOS phosphorylation contribute to increased arteriolar NO release during juvenile growth

Nitric oxide (NO) mediates a major portion of arteriolar endothelium-dependent dilation in adults, but indirect evidence has suggested that NO contributes minimally to these responses in the young. Isolated segments of arterioles were studied in vitro to verify this age-related increase in NO release and investigate the mechanism by which it occurs. Directly measured NO release induced by ACh or the Ca(2+) ionophore A-23187 was five- to sixfold higher in gracilis muscle arterioles from 42- to 46-day-old (juvenile) rats than in those from 25- to 28-day-old (weanling) rats. There were no differences between groups in arteriolar endothelial NO synthase (eNOS) expression or tetrahydrobiopterin levels, and arteriolar l-arginine levels were lower in juvenile vessels than in weanling vessels (104 ± 6 vs.126 ± 3 pmol/mg). In contrast, agonist-induced eNOS Thr(495) dephosphorylation and eNOS Ser(1177) phosphorylation (events required for maximal activity) were up to 30% and 65% greater, respectively, in juvenile vessels. Juvenile vessels did not show increased expression of enzymes that mediate these events [protein phosphatases 1 and 2A and PKA and PKB (Akt)] or heat shock protein 90, which facilitates Ser(1177) phosphorylation. However, agonist-induced colocalization of heat shock protein 90 with eNOS was 34-66% greater in juvenile vessels than in weanling vessels, and abolition of this difference with geldanamycin also abolished the difference in Ser(1177) phosphorylation between groups. These findings suggest that growth-related increases in arteriolar NO bioavailability may be due at least partially to changes in the regulation of eNOS phosphorylation and increased signaling activity, with no change in the abundance of eNOS signaling proteins.

Altered coronary vascular control during cold stress in healthy older adults

Cardiovascular-related mortality increases in the cold winter months, particularly in older adults. Previously, we reported that determinants of myocardial O(2) demand, such as the rate-pressure product, increase more in older adults compared with young adults during cold stress. The aim of the present study was to determine if aging influences the coronary hemodynamic response to cold stress in humans. Transthoracic Doppler echocardiography was used to noninvasively measure peak coronary blood velocity in the left anterior descending artery before and during acute (20 min) whole body cold stress in 10 young adults (25 ± 1 yr) and 11 older healthy adults (65 ± 2 yr). Coronary vascular resistance (diastolic blood pressure/peak coronary blood velocity), coronary perfusion time fraction (coronary perfusion time/R-R interval), and left ventricular wall stress were calculated. We found that cooling (via a water-perfused suit) increased left ventricular wall stress, a primary determinant of myocardial O(2) consumption, in both young and older adults, although the magnitude of this increase was nearly twofold greater in older adults (change of 9.1 ± 3.5% vs. 17.6 ± 3.2%, P < 0.05, change from baseline in young and older adults and young vs. older adults). Despite the increased myocardial O(2) demand during cooling, coronary vasodilation (decreased coronary vascular resistance) occurred only in young adults (3.22 ± 0.23 to 2.85 ± 0.18 mmHg·cm(-1)·s(-1), P < 0.05) and not older adults (3.97 ± 0.24 to 3.79 ± 0.27 mmHg·cm(-1)·s(-1), P > 0.05). Consistent with a blunted coronary vascular response, absolute coronary perfusion time tended to decrease (P = 0.13) and coronary perfusion time fraction decreased (P < 0.05) during cooling in older adults but not young adults. Collectively, these data suggest that older adults demonstrate an altered coronary hemodynamic response to acute cold stress.

Caloric restriction: powerful protection for the aging heart and vasculature

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in the United States. Research has shown that the majority of the cardiometabolic alterations associated with an increased risk of CVD (e.g., insulin resistance/type 2 diabetes, abdominal obesity, dyslipidemia, hypertension, and inflammation) can be prevented, and even reversed, with the implementation of healthier diets and regular exercise. Data from animal and human studies indicate that more drastic interventions, i.e., calorie restriction with adequate nutrition (CR), may have additional beneficial effects on several metabolic and molecular factors that are modulating cardiovascular aging itself (e.g., cardiac and arterial stiffness and heart rate variability). The purpose of this article is to review the current knowledge on the effects of CR on the aging of the cardiovascular system and CVD risk in rodents, monkeys, and humans. Taken together, research shows that CR has numerous beneficial effects on the aging cardiovascular system, some of which are likely related to reductions in inflammation and oxidative stress. In the vasculature, CR appears to protect against endothelial dysfunction and arterial stiffness and attenuates atherogenesis by improving several cardiometabolic risk factors. In the heart, CR attenuates age-related changes in the myocardium (i.e., CR protects against fibrosis, reduces cardiomyocyte apoptosis, prevents myosin isoform shifts, etc.) and preserves or improves left ventricular diastolic function. These effects, in combination with other benefits of CR, such as protection against obesity, diabetes, hypertension, and cancer, suggest that CR may have a major beneficial effect on health span, life span, and quality of life in humans.

ROS-induced ROS release in vascular biology: redox-redox signaling

The involvement of reactive oxygen species (ROS) in regulating vascular function both in normal vessels and as part of an adaptive response during disease has been intensively studied. From the recognition that ROS serve as important signaling molecules has emerged multiple lines of evidence that there is a functional connectivity between intracellular sites of ROS production. This cross talk has been termed ROS-induced ROS release (RIRR) and is supported by a variety of observations showing that RIRR is a common mechanism for ROS amplification and regional ROS generation. The compartmentalization of ROS production within a cell is critical to its signaling function and is facilitated by microlocalization of specific scavengers. This review will provide descriptions and examples of important mechanisms of RIRR.