Age-dependent impairment of coronary collateral development in humans

A Chinese scoring system for predicting successful retrograde collateral traverse in patients with chronic total coronary occlusion

BACKGROUND

Retrograde approach technique has been challenging in percutaneous coronary interventional treatment of chronic total occlusion (CTO) coronary disease. The present study endeavors to determine a novel Chinese scoring system for predicting successful collateral channels traverse via retrograde approach.

METHODS

The demographic characteristics and angiographic characteristics of 309 CTO patient were analyzed by univariable and multivariable analysis for selecting potential predictors. And the nomogram was used to establish the scoring system. Then it was evaluated by the internal and external validation.

RESULTS

The predictors of Age, Connections between collateral channels and recipient vessels, and Channel Tortuosity (ACT) were identified with univariable and multivariable analysis and employed to the ACT score system. With acceptable calibrations, the area under curve of the scoring system and the external validation were 0.826 and 0.816 respectively. Based on score, the predictors were divided into three risk categories and it showed a consistent prediction power in the validation cohort.

CONCLUSIONS

The novel Chinese ACT score is a reliable tool for predicting successful retrograde collateral traverse.

Endothelial Senescence and Its Impact on Angiogenesis in Alzheimer's Disease

Endothelial cells are constantly exposed to environmental stress factors that, above a certain threshold, trigger cellular senescence and apoptosis. The altered vascular function affects new vessel formation and endothelial fitness, contributing to the progression of age-related diseases. This narrative review highlights the complex interplay between senescence, oxidative stress, extracellular vesicles, and the extracellular matrix and emphasizes the crucial role of angiogenesis in aging and Alzheimer's disease. The interaction between the vascular and nervous systems is essential for the development of a healthy brain, especially since neurons are exceptionally dependent on nutrients carried by the blood. Therefore, anomalies in the delicate balance between pro- and antiangiogenic factors and the consequences of disrupted angiogenesis, such as misalignment, vascular leakage and disturbed blood flow, are responsible for neurodegeneration. The implications of altered non-productive angiogenesis in Alzheimer's disease due to dysregulated Delta-Notch and VEGF signaling are further explored. Additionally, potential therapeutic strategies such as exercise and caloric restriction to modulate angiogenesis and vascular aging and to mitigate the associated debilitating symptoms are discussed. Moreover, both the roles of extracellular vesicles in stress-induced senescence and as an early detection marker for Alzheimer's disease are considered. The intricate relationship between endothelial senescence and angiogenesis provides valuable insights into the mechanisms underlying angiogenesis-related disorders and opens avenues for future research and therapeutic interventions.

The association of serum uric acid/albumin ratio with the development of coronary collateral circulation in patients with chronic total occluded coronary arteries

Introduction: Coronary collateral circulation (CCC) develops in chronic total occluded (CTO) vessels and protects the myocardium against ischemia in addition to the improvement of cardiac functions. Poor CCC is related to adverse cardiac events as well as poor prognosis. Serum uric acid/albumin ratio (UAR) has emerged as a novel marker associated with poor cardiovascular outcomes. We aimed to investigate whether there was an association between UAR and poor CCC in CTO patients. Methods: This study was comprised of 212 patients with CTO (92 with poor CCC and 120 with good CCC). All patients were graded based on Rentrop scores to poor CCC (Rentrop scores 0 and 1) and good CCC (Rentrop scores 2 and 3). Results: Poor CCC patients had higher frequencies of diabetes mellitus, triglyceride levels, Syntax and Gensini scores, uric acid, and UAR and lower lymphocyte, high-density lipoprotein cholesterol, and ejection fraction when compared to good CCC patients. UAR was an independent predictor of poor CCC in CTO patients. Furthermore, UAR had a better discriminative ability for patients with poor CCC from good CCC compared to serum uric acid and albumin. Conclusion: Based on the results of the study, the UAR could be used to detect poor CCC in CTO patients.

Endothelial cell dysfunction: Implications for the pathogenesis of peripheral artery disease

Peripheral artery disease (PAD) is caused by occluded or narrowed arteries that reduce blood flow to the lower limbs. The treatment focuses on lifestyle changes, management of modifiable risk factors and vascular surgery. In this review we focus on how Endothelial Cell (EC) dysfunction contributes to PAD pathophysiology and describe the largely untapped potential of correcting endothelial dysfunction. Moreover, we describe current treatments and clinical trials which improve EC dysfunction and offer insights into where future research efforts could be made. Endothelial dysfunction could represent a target for PAD therapy.

Endothelial Progenitor Cells: An Appraisal of Relevant Data from Bench to Bedside

The mobilization of endothelial progenitor cells (EPCs) into circulation from bone marrow is well known to be present in several clinical settings, including acute coronary syndrome, heart failure, diabetes and peripheral vascular disease. The aim of this review was to explore the current literature focusing on the great opportunity that EPCs can have in terms of regenerative medicine.

Fluid shear stress regulates placental growth factor expression via heme oxygenase 1 and iron

Increased fluid shear stress (FSS) is a key initiating stimulus for arteriogenesis, the outward remodeling of collateral arterioles in response to upstream occlusion. Placental growth factor (PLGF) is an important arteriogenic mediator. We previously showed that elevated FSS increases PLGF in a reactive oxygen species (ROS)-dependent fashion both in vitro and ex vivo. Heme oxygenase 1 (HO-1) is a cytoprotective enzyme that is upregulated by stress and has arteriogenic effects. In the current study, we used isolated murine mesentery arterioles and co-cultures of human coronary artery endothelial cells (EC) and smooth muscle cells (SMC) to test the hypothesis that HO-1 mediates the effects of FSS on PLGF. HO-1 mRNA was increased by conditions of increased flow and shear stress in both co-cultures and vessels. Both inhibition of HO-1 with zinc protoporphyrin and HO-1 knockdown abolished the effect of FSS on PLGF. Conversely, induction of HO-1 activity increased PLGF. To determine which HO-1 product upregulates PLGF, co-cultures were treated with a CO donor (CORM-A1), biliverdin, ferric ammonium citrate (FAC), or iron-nitrilotriacetic acid (iron-NTA). Of these FAC and iron-NTA induced an increase PLGF expression. This study demonstrates that FSS acts through iron to induce pro-arteriogenic PLGF, suggesting iron supplementation as a novel potential treatment for revascularization.

Use of Oral Anticoagulation and Diabetes Do Not Inhibit the Angiogenic Potential of Hypoxia Preconditioned Blood-Derived Secretomes

Patients suffering from tissue ischemia, who would greatly benefit from angiogenesis-promoting therapies such as hypoxia preconditioned blood-derived secretomes commonly receive oral anticoagulation (OA) and/or have diabetes mellitus (DM). In this study, we investigated the effect of OA administration on the in vitro angiogenic potential of hypoxia preconditioned plasma (HPP) and serum (HPS), prepared from nondiabetic/diabetic subjects who did not receive OA (n = 5) or were treated with acetylsalicylic acid (ASA, n = 8), ASA + clopidogrel (n = 10), or nonvitamin K antagonist oral anticoagulants (n = 7) for longer than six months. The effect of DM was differentially assessed by comparing HPP/HPS obtained from nondiabetic (n = 8) and diabetic (n = 16) subjects who had not received OA in the past six months. The concentration of key proangiogenic (vascular endothelial growth factor or VEGF) and antiangiogenic (thrombospondin-1 or TSP-1 and platelet factor-4 or PF-4) protein factors in HPP/HPS was analyzed via ELISA, while their ability to induce microvessel formations was examined in endothelial cell cultures. We found that OA use significantly reduced VEGF levels in HPP, but not HPS, compared to non-OA controls. While HPP and HPS TSP-1 levels remained largely unchanged as a result of OA usage, HPS PF-4 levels were significantly reduced in samples obtained from OA-treated subjects. Neither OA administration nor DM appeared to significantly reduce the ability of HPP or HPS to induce microvessel formations in vitro. These findings indicate that OA administration does not limit the angiogenic potential of hypoxia preconditioned blood-derived secretomes, and therefore, it does not prohibit the application of these therapies for supporting tissue vascularization and wound healing in healthy or diabetic subjects.

Reduced expression of microRNA-130a promotes endothelial cell senescence and age-dependent impairment of neovascularization

Aging is associated with impaired neovascularization in response to ischemia. MicroRNAs are small noncoding RNAs emerging as key regulators of physiological and pathological processes. Here we investigated the potential role of microRNAs in endothelial cell senescence and age-dependent impairment of neovascularization. Next generation sequencing and qRT-PCR analyses identified miR-130a as a pro-angiogenic microRNA which expression is significantly reduced in old mouse aortic endothelial cells (ECs). Transfection of young ECs with a miR-130a inhibitor leads to accelerated senescence and reduced angiogenic functions. Conversely, forced expression of miR-130a in old ECs reduces senescence and improves angiogenesis. In a mouse model of hindlimb ischemia, intramuscular injection of miR-130a mimic in older mice restores blood flow recovery and vascular densities in ischemic muscles, improves mobility and reduces tissue damage. miR-130a directly targets antiangiogenic homeobox genes MEOX2 and HOXA5. MEOX2 and HOXA5 are significantly increased in the ischemic muscles of aging mice, but forced expression of miR-130a reduces the expression of these factors. miR-130a treatment after ischemia is also associated with increased number and improved functional activities of pro-angiogenic cells (PACs). Forced expression of miR-130a could constitute a novel strategy to improve blood flow recovery and reduce ischemia in older patients with ischemic vascular diseases.

Cardiac tissue remodeling in healthy aging: the road to pathology

This review aims to highlight the normal physiological remodeling that occurs in healthy aging hearts, including changes that occur in contractility, conduction, valve function, large and small coronary vessels, and the extracellular matrix. These "normal" age-related changes serve as the foundation that supports decreased plasticity and limited ability for tissue remodeling during pathophysiological states such as myocardial ischemia and heart failure. This review will identify populations at greater risk for poor tissue remodeling in advanced age along with present and future therapeutic strategies that may ameliorate dysfunctional tissue remodeling in aging hearts.

Effect of Recruitment of Acute Coronary Collaterals on In-Hospital Mortality and on Left Ventricular Function in Patients Presenting With ST Elevation Myocardial Infarction

Recruitment of the coronary collateral circulation is frequently observed during ST elevation myocardial infarction (STEMI) and is of uncertain significance. The aim of this study was to identify and determine the predictors and prognostic implications of the presence of robust collaterals during STEMI. All patients presenting to a large tertiary centre with a STEMI undergoing percutaneous coronary intervention from 2010 to 2018 were reviewed. Patients with poor collateral recruitment were defined as those with Rentrop grade 0 or 1 collaterals, whilst patients with robust collateral recruitment were defined as Rentrop grade 2 or 3. A total of 1,625 patients were included in the study, with 1,280 (78.8%) patients having poor collateral recruitment and 345 patients (21.2%) having robust collateral recruitment. Patients with robust collaterals were younger (63.1 vs 65.1 years, p < 0.05), had a longer ischemic time (628.5 minutes vs 433.1 minutes, p < 0.0001), and more likely to have a chronic total occlusion of a noninfarct related artery (10.4% vs 5.3%, p < 0.001). The presence of robust collaterals was associated with higher rates of normal or mildly impaired left ventricular function (83.5% vs 63.2%, p < 0.0001) and lower in-hospital mortality (2.1% vs 7.6%, p < 0.0001). After correcting for left ventricular function, collateral recruitment was not an independent predictor of mortality. In conclusion, in patients presenting with STEMI, the presence of robust coronary collaterals appears to be associated with improved left ventricular function. Further research is required to identify mechanisms of collateral maturation and recruitment.

Association of atherosclerotic plaque features with collateral circulation status in elderly patients with chronic carotid stenosis

OBJECTIVE

To determine the association of carotid plaque features with collateral circulation status in elderly patients with moderate to severe carotid stenosis.

METHODS

Elderly patients (> 60 years) with moderate to severe carotid stenosis were recruited and categorized into good and poor collateral circulation groups, and underwent magnetic resonance imaging and computed tomography imaging. The carotid plaque features including lipid-rich necrotic core, intraplaque hemorrhage, calcification, and fibrous cap rupture (FCR) were evaluated, and maximum wall thickness, normalized wall index (NWI), and luminal stenosis were measured. The association between these variables and collateral circulation status was analyzed.

RESULTS

Of the 97 patients (78 males, mean age: 69.0 ± 6.1 years), 19 (19.6%) had poor collaterals. The poor collateral group had a significantly higher NWI (93.7% ± 5.0% vs. 89.0% ± 7.9%, P = 0.011), a greater extent of stenosis (80.0% ± 11.4% vs. 75.3% ± 9.4%, P = 0.036) and FCR (84.2% vs. 55.1%, P = 0.020) compared with good collateral group. Carotid NWI (OR = 3.83, 95% CI: 1.36-10.82, P = 0.011) and more FCR (OR = 6.77, 95% CI: 1.35-33.85, P = 0.020) were associated with poor collateral circulation after adjustment for the confounding factors. The combination of NWI, FCR, systolic blood pressure, and triglycerides had the highest area-under-the-curve (AUC = 0.85) for detection of poor collaterals.

CONCLUSIONS

Carotid plaque features, specifically NWI and FCR, are independently associated with poor collateral circulation, and the combination of carotid plaque features and traditional risk factors has a stronger predictive value for poor collateral circulation than plaque features alone.

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.

Long Non-Coding RNA in Vascular Disease and Aging

Cardiovascular diseases are the most prominent cause of death in Western society, especially in the elderly. With the increasing life expectancy, the number of patients with cardiovascular diseases will rise in the near future, leading to an increased healthcare burden. There is a need for new therapies to treat this growing number of patients. The discovery of long non-coding RNAs has led to a novel group of molecules that could be considered for their potential as therapeutic targets. This review presents an overview of long non-coding RNAs that are regulated in vascular disease and aging and which might therefore give insight into new pathways that could be targeted to diagnose, prevent, and/or treat vascular diseases.

Angiogenesis, Cancer, and Vascular Aging

Several lines of evidence have revealed that the angiogenic response to ischemic injury declines with age, which might account for the increased morbidity and mortality of cardiovascular disease (CVD) among the elderly. While impairment of angiogenesis with aging leads to delayed wound healing or exacerbation of atherosclerotic ischemic diseases, it also inhibits the progression of cancer. Age-related changes of angiogenesis have been considered to at least partly result from vascular aging or endothelial cell senescence. There is considerable evidence supporting the hypothesis that vascular cell senescence contributes to the pathogenesis of age-related CVD, suggesting that vascular aging could be an important therapeutic target. Since therapeutic angiogenesis is now regarded as a promising concept for patients with ischemic CVD, it has become even more important to understand the detailed molecular mechanisms underlying impairment of angiogenesis in older patients. To improve the usefulness of therapeutic angiogenesis, approaches are needed that can compensate for impaired angiogenic capacity in the elderly while not promoting the development or progression of malignancy. In this review, we briefly outline the mechanisms of angiogenesis and vascular aging, followed by a description of how vascular aging leads to impairment of angiogenesis. We also examine potential therapeutic approaches that could enhance angiogenesis and/or vascular function in the elderly, as well as discussing the possibility of anti-senescence therapy or reversal of endothelial cell senescence.

Collateral Growth in the Peripheral Circulation: A Review

Arterial occlusive diseases are a major cause of morbidity and death in the United States. The enlargement of pre-existing vessels, which bypass the site of arterial occlusion, provide a natural way for the body to compensate for such obstructions. Individuals differ in their capacity to develop collateral vessels. In recent years much attention has been focused upon therapy to promote collateral development, primarily using individual growth factors. Such studies have had mixed results. Persistent controversies exist regarding the initiating stimuli, the processes involved in enlargement, the specific vessels that should be targeted, and the most appropriate terminology. Consequently, it is now recognized that more research is needed to extend our knowledge of the complex process of collateral growth. This basic science review addresses five questions essential in understanding current problems in collateral growth research and the development of therapeutic interventions.

Time-related alteration in flow- (shear stress-) mediated remodeling in resistance arteries from spontaneously hypertensive rats

Hypertension is a major risk factor for cardiovascular disorders. As flow-mediated outward remodeling has a key role in postischemic revascularization, we investigated this remodeling in mesenteric resistance arteries of normotensive (WKY) and spontaneously hypertensive rats (SHRs) aged 3 to 9 months. Sequential ligation of mesenteric resistance arteries allowed modifying blood flow in vivo, thus exposing arteries to low, normal, or high flow. After 1, 3, 8, or 24 weeks, arteries were isolated for in vitro study. High flow (HF) induced outward hypertrophic remodeling in WKY rats after 1 week and persisted until 24 weeks without change in wall to lumen ratio. In SHRs, diameter increase was delayed, occurring only after 3 weeks. Nevertheless, it was reduced at 8 weeks and no longer significant after 24 weeks. In parallel, media cross-section area increased more with time in SHRs than in WKY rats and this was associated with increased contractility and oxidative stress with decreased NO-dependent relaxation. Low flow induced progressive inward remodeling until 24 weeks in both strains with excessive hypertrophy in SHRs. Thus, a chronic increase in flow induced transitory diameter expansion and long-lasting hypertrophy in SHRs. This could contribute to the higher susceptibility of hypertensive subjects to ischemic diseases.

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.

Predictor of poor coronary collaterals in elderly population with significant coronary artery disease

BACKGROUND

Coronary collateral circulation plays an important role in protecting myocardium from ischemia and reducing cardiovascular events. Advanced age might be associated with poor coronary collateral development and cardiovascular outcome. However, limited studies investigate the predictors for collateral development in the elderly population.

METHODS

The authors evaluated 950 consecutive patients undergoing coronary angiography and finally analyzed 207 patients of 65 years or more. The collateral scoring system developed by Rentrop was used to classify patients into those with poor or good collateral formation.

RESULTS

The patients with poor collateral were older age, had lower incidence of smoking, more male sex, had fewer diseased vessels and had a trend to be diabetic. Multivariate analysis showed age (odds ratio (OR) = 1.068; P = 0.019), diabetes (OR = 2.681; P = 0.003) and diseased vessels numbers (OR = 0.337; P < 0.001) were significant predictors of poor collaterals development. Furthermore, age and diabetes have a synergistic effect on poor collateral development (P = 0.041 for interaction).

CONCLUSIONS

Even in the elderly population, age and diabetes might negatively influence the coronary collaterals development.

Loss of bcl-2 during the senescence exacerbates the impaired angiogenic functions in endothelial cells by deteriorating the mitochondrial redox state

Ageing is an important risk factor for ischemic cardiovascular diseases, although its underlying molecular mechanisms remain to be elucidated. Here, we report a crucial role of Bcl-2 in the impaired angiogenic functions in senescent endothelial cells (ECs) by modulating the mitochondrial redox state. Cellular senescence impaired angiogenic functions in ECs without attenuating the mitogen-activated protein kinase or Akt signaling, and vascular endothelial growth factor receptor 2 or Tie-2 expressions. We identified that Bcl-2 expression was markedly reduced in 3 independent models for senescent ECs, and pharmacological inhibition, as well as small interfering RNA-mediated gene silencing of Bcl-2, significantly impaired the angiogenic functions in young ECs. Bcl-2 has an antioxidative role by locating the glutathione at mitochondria, and we found that mitochondrial oxidative stress was significantly augmented in senescent ECs, in association with reduced mitochondria-associated glutathione. Transfection of Bcl-2 in senescent ECs significantly reduced the mitochondrial oxidative stress, restored the mitochondrial membrane potential, and improved the angiogenic capacity. Furthermore, gene transfer of Bcl-2 using adenovirus significantly improved the in vivo angiogenesis in the Matrigel plugs implanted into aged mice, whereas the Bcl-2 inhibitor reduced the angiogenesis in the Matrigel plugs implanted into young mice. Together, Bcl-2 plays a crucial role in the regulation of the mitochondrial redox state in ECs, and, thus, loss of Bcl-2 during the senescence exacerbates the impaired angiogenesis by augmenting the mitochondrial oxidative stress.

Cardiovascular risk factors and collateral artery formation

Arterial lumen narrowing and vascular occlusion is the actual cause of morbidity and mortality in atherosclerotic disease. Collateral artery formation (arteriogenesis) refers to an active remodelling of non-functional vascular anastomoses to functional collateral arteries, capable to bypass the site of obstruction and preserve the tissue that is jeopardized by ischaemia. Hemodynamic forces such as shear stress and wall stress play a pivotal role in collateral artery formation, accompanied by the expression of various cytokines and invasion of circulating leucocytes. Arteriogenesis hence represents an important compensatory mechanism for atherosclerotic vessel occlusion. As arteriogenesis mostly occurs when lumen narrowing by atherosclerotic plaques takes place, presence of cardiovascular risk factors (e.g. hypertension, hypercholesterolaemia and diabetes) is highly likely. Risk factors for atherosclerotic disease affect collateral artery growth directly and indirectly by altering hemodynamic forces or influencing cellular function and proliferation. Adequate collateralization varies significantly among atherosclerotic patients, some profit from the presence of extensive collateral networks, whereas others do not. Cardiovascular risk factors could increase the risk of adverse cardiovascular events in certain patients because of the reduced protection through an alternative vascular network. Likewise, drugs primarily thought to control cardiovascular risk factors might contribute or counteract collateral artery growth. This review summarizes current knowledge on the influence of cardiovascular risk factors and the effects of cardiovascular medication on the development of collateral vessels in experimental and clinical studies.

Abnormal nitric oxide production in aged rat mesenteric arteries is mediated by NAD(P)H oxidase-derived peroxide

Previous work in our laboratory showed increased basal periarterial nitric oxide (NO) and H2O2 concentrations in the spontaneously hypertensive rat, characterized by oxidant stress, as well as impaired flow-mediated NO production that was corrected by a reduction of periarterial H2O2. Aging is also associated with an increase in vascular reactive oxygen species and results in abnormal vascular function. The current study was designed to assess the role of H2O2 in regulating NO production during vascular aging. In vivo, real-time NO and H2O2 concentrations were measured by microelectrodes in mesenteric arteries of retired breeder (aged; 8-12 mo) and young (2 to 3 mo) Wistar-Kyoto rats under conditions of altered flow. The results in aged rats revealed elevated basal NO (1,611+/-286 vs. 793+/-112 nM, P<0.05) and H2O2 concentrations (16+/-2 vs. 9+/-1 microM, P<0.05) and a flow-mediated increase in H2O2 but not NO production. Pretreatment of aged rats with the antioxidant apocynin lowered both basal H2O2 (8+/-1 microM) and NO (760+/-102 nM) to young levels and restored flow-mediated NO production. Similar results were obtained with the NAD(P)H oxidase inhibitor gp91ds-tat. In addition, acute incubation with topical polyethylene-glycolated catalase lowered the baseline NO concentration and restored flow-mediated NO production. Taken together, the data indicate that elevated baseline and suppressed flow-mediated NO production in aged Wistar-Kyoto rats are mediated by NAD(P)H oxidase-derived H2O2.

Antioxidants reverse age-related collateral growth impairment

Aging is a major risk factor for the development of cardiovascular diseases, including arterial occlusive disease. Oxidant stress increases with age, and may be a significant factor contributing to vascular dysfunction and disease. We have shown that aging and hypertension impair collateral growth, the natural compensatory response to arterial occlusive disease, and that antioxidants restore collateral growth in young hypertensive rats. The aim of this study was to test the hypothesis that oxidant stress mediates collateral growth impairment in nondiseased, aged rats. Ileal arteries were induced to become collaterals via ligation of adjacent arteries. Growth was assessed at 7 days by repeated in vivo measurements and comparison to same-animal control arteries. Collateral diameter enlargement did not occur in aged rats, but luminal expansion was stimulated by pretreatment with tempol. Co-administration of L-NAME with tempol prevented tempol-mediated collateral development. Expression of p22(phox) mRNA was increased in aged versus young rat arteries, suggesting NAD(P)H oxidase as a source of reactive oxygen species. Treatment with apocynin increased collateral growth capacity, whether administered prior to, or 7 days following, arterial ligation. The results suggest that antioxidant treatment may be useful in promoting collateral growth to compensate for age-related arterial occlusive disease.

NAD(P)H oxidase-derived peroxide mediates elevated basal and impaired flow-induced NO production in SHR mesenteric arteries in vivo

Nitric oxide (NO) and reactive oxygen species (ROS) have fundamentally important roles in the regulation of vascular tone and remodeling. Although arterial disease and endothelial dysfunction alter NO and ROS levels to impact vasodilation and vascular structure, direct measurements of these reactive species under in vivo conditions with flow alterations are unavailable. In this study, in vivo measurements of NO and H2O2 were made on mesenteric arteries to determine whether antioxidant therapies could restore normal NO production in spontaneously hypertensive rats (SHR). Flow was altered from approximately 50-200% of control in anesthetized Wistar-Kyoto rats (WKY) and SHR by selective placement of microvascular clamps on adjacent arteries while NO and H2O2 were directly measured with microelectrodes. Relative to WKY, SHR had significantly increased baseline NO and H2O2 concentrations (2,572 +/- 241 vs. 1,059 +/- 160 nM, P < 0.01; and 26 +/- 7 vs. 7 +/- 1 microM, P < 0.05, respectively). With flow elevation, H2O2 but not NO increased in SHR; NO but not H2O2 was elevated in WKY. Apocynin and polyethylene-glycolated catalase decreased baseline SHR NO and H2O2 to WKY levels and restored flow-mediated NO production. Suppression of NAD(P)H oxidase with gp91ds-tat decreased SHR H2O2 to WKY levels. Addition of topical H2O2 to increase peroxide to the basal concentration measured in SHR elevated WKY NO to levels observed in SHR. The results support the hypothesis that increased vascular peroxide in SHR is primarily derived from NAD(P)H oxidase and increases NO concentration to levels that cannot be further elevated with increased flow. Short-term and even acute administration of antioxidants are able to restore normal flow-mediated NO signaling in young SHR.

Impact of genetic background and aging on mesenteric collateral growth capacity in Fischer 344, Brown Norway, and Fischer 344 x Brown Norway hybrid rats

Available studies indicate that both genetic background and aging influence collateral growth capacity, but it is not known how their combination affects collateral growth. We evaluated collateral growth induced by ileal artery ligation in Fischer 344 (F344), Brown Norway (BN), and the first generation hybrid of F344 x BN (F1) rats available for aging research from the National Institute on Aging. Collateral growth was determined by paired diameter measurements in anesthetized rats immediately and 7 days postligation. In 3-mo-old rats, significant collateral growth occurred only in BN (35% +/- 11%, P < 0.001). The endothelial cell number in arterial cross sections was also determined, since this precedes shear-mediated luminal expansion. When compared with the same animal controls, the intimal cell number was increased only in BN rats (92% +/- 21%, P < 0.001). The increase in intimal cell number and the degree of collateral luminal expansion in BN rats was not affected by age from 3 to 24 mo. Immunohistochemical studies demonstrated that intimal cell proliferation was much greater in the collaterals of BN than of F1 rats. The remarkable difference between these three strains of rats used in aging research and the lack of an age-related impairment in the BN rats are novel observations. These rat strains mimic clinical observations of interindividual variation in collateral growth capacity and the impact of age on arteriogenesis and should be useful models to investigate the molecular mechanisms responsible for such differences.

Influence of oxidative stress on the development of collateral circulation in total coronary occlusions

OBJECTIVES

The purpose of this study was to investigate whether the levels of total antioxidant capacity (TAC), total peroxide and oxidative stress index (OSI) are associated with the development of collaterals in total coronary occlusions.

DESIGN AND METHODS

Our study group contained 176 consecutive men patients with single-vessel TCO, 94 of whom had poorly developed coronary collateral, while 82 had well-developed coronary collateral. TAC and total peroxide concentration were measured of plasma. The ratio of TAC to total peroxide was accepted as an indicator of oxidative stress.

RESULTS

The values of total peroxide and OSI in the Group I were significantly lower than that in Group II (p<0.001, for both). TAC levels were significantly higher in patients with poorly developed collaterals than in well-developed collateral group (p<0.001). OSI values were also significantly different among the Rentrop class-0, -1, -2 and -3 (ANOVA p<0.001). We found significant correlations between collaterals score and TAC, total peroxide and OSI levels (p<0.001 for all). In multiple linear regression analysis, total peroxide and OSI were independent predictors of collaterals score (p=0.006 and p<0.001 respectively).

CONCLUSION

This study clearly demonstrates that the level of OSI is independently and positively associated with the presence of collateral circulation in total coronary occlusion patients.

The role of the renin-angiotensin system and oxidative stress in spontaneously hypertensive rat mesenteric collateral growth impairment

Recent clinical and animal studies have shown that collateral artery growth is impaired in the presence of vascular risk factors, including hypertension. Available evidence suggests that angiotensin-converting enzyme inhibitors (ACEI) promote collateral growth in both hypertensive humans and animals; however, the specific mechanisms are not established. This study evaluated the hypothesis that collateral growth impairment in hypertension is mediated by excess superoxide produced by NAD(P)H oxidase in response to stimulation of the ANG II type 1 receptor. After ileal artery ligation, mesenteric collateral growth did not occur in untreated, young, spontaneously hypertensive rats. Significant luminal expansion occurred in collaterals of spontaneously hypertensive rats treated with the superoxide dismutase mimetic tempol, the NAD(P)H oxidase inhibitor apocynin, and the ACEI captopril, but not ANG II type 1 (losartan) or type 2 (PD-123319) receptor blockers. The ACEI enalapril produced equivalent reduction of arterial pressure as captopril but did not promote luminal expansion. This suggests the effects of captopril on collateral growth might result from its antioxidant properties. RT-PCR demonstrated that ANG II type 1 receptor and angiotensinogen expression was reduced in collaterals of untreated rats. This local suppression of the renin angiotensin system provides a potential explanation for the lack of effect of enalapril and losartan on collateral growth. The results demonstrate the capability of antioxidant therapies, including captopril, to reverse impaired collateral artery growth and the novel finding that components of the local renin angiotensin system are naturally suppressed in collaterals.

Recent insights into human coronary collateral development

Enhancement of coronary collateral function is an intriguing approach to the preservation of ischaemic myocardium. Coronary collateral development consists of collateral recruitment and collateral growth. Collateral growth encompasses proliferation of capillaries in the ischaemic area (angiogenesis) and maturation of pre-existing collateral vessels (arteriogenesis), with the latter being more relevant in humans. Therefore, treatment intended directly for arteriogenesis of collateral vessels appears to be more effective. Promotion of coronary collateral growth has many attractive features, particularly in patients with angina who are not indicated for percutaneous coronary intervention or coronary artery bypass grafting surgery. A complete elucidation of the remaining practical and mechanistic questions of arteriogenesis may lead to a new remedy capable of developing collateral vessels more effectively.

Invasive and non-invasive evaluation of spontaneous arteriogenesis in a novel porcine model for peripheral arterial obstructive disease

Our current knowledge regarding the efficacy of factors stimulating collateral artery growth in the peripheral circulation primarily stems from models in small animals. However, experimental models in large sized animals are a prerequisite for extrapolation of growth factor therapy to patients with peripheral atherosclerotic obstructive disease. Therefore, we have developed a novel porcine femoral artery ligation model using non-invasive and invasive evaluation techniques. In 12 young farm pigs and nine older minipigs, a ligation of the superficial femoral artery was performed. Using an intra-arterial catheter, phosphate buffered saline (PBS) was administered with a first-pass over the collateral vascular bed. Directly after ligation as well as after 2 weeks of continuous infusion of PBS, perfusion of the leg was measured using various flow and pressure parameters. Using a pump driven extracorporal system, collateral conductance was determined under maximal vasodilatation. Conductance decreased after acute ligation to similar levels in both young farm pigs as well as the older minipigs (both 9.3% of normal perfusion) and recovered after 2 weeks to a higher value in farm pigs compared with minipigs (22.4 vs. 12.7% of normal; P<0.05). Angiography using both X-ray and magnetic resonance imaging was performed to visualize the formed collateral arteries. To the best of our knowledge this is the first in vivo pig model for hemodynamic assessment of growth of collateral arteries in the peripheral circulation, that is suitable for evaluation of arteriogenic effects of growth factors or genes.

Plasma level of homocysteine is inversely-associated with the development of collateral circulation in patients with single-vessel coronary artery disease

Homocysteine induces endothelial injury and inhibits endothelial cell proliferation, which is a key role in angiogenesis. The purpose of this study was to investigate whether the plasma level of homocysteine is associated with the development of collaterals in patients with single-vessel coronary artery disease (CAD). Among a series of 105 male patients with angiographic estimation, 49 with single-vessel CAD were intensively investigated. Development of collaterals was classified by Rentrop's method. Univariate and multivariate analyses revealed that hyperhomocysteinemia negatively affected the development of collaterals (p=0.0015 and 0.0011, odds ratio 0.69, 95% confidence interval 0.52-0.90), whereas the duration of angina and percent stenosis evaluated by quantitative coronary angiography had a positive affect. Moreover, the level of homocysteine in the group with poorly developed collaterals (n=7, Rentrop class 0 and 1) was significantly higher than that in the group with well-developed collaterals (n=12, Rentrop class 2 and 3) of the patients with single-vessel disease showing total occlusion (p=0.034). This study clearly demonstrates that the plasma level of homocysteine is independently and inversely associated with the development of collateral circulation in CAD patients. Homocysteine might be a new undesirable aspect of ischemic heart disease through its inhibition of collateral development.