The human coronary collateral circulation: development and clinical importance

Endothelial β1 Integrin-Mediated Adaptation to Myocardial Ischemia

BACKGROUND

 Short episodes of myocardial ischemia can protect from myocardial infarction. However, the role of endothelial β1 integrin in these cardioprotective ischemic events is largely unknown.

OBJECTIVE

 In this study we investigated whether endothelial β1 integrin is required for cardiac adaptation to ischemia and protection from myocardial infarction.

METHODS

 Here we introduced transient and permanent left anterior descending artery (LAD) occlusions in mice. We inhibited β1 integrin by intravenous injection of function-blocking antibodies and tamoxifen-induced endothelial cell (EC)-specific deletion of Itgb1. Furthermore, human ITGB1 was silenced in primary human coronary artery ECs using small interfering RNA. We analyzed the numbers of proliferating ECs and arterioles by immunohistochemistry, determined infarct size by magnetic resonance imaging (MRI) and triphenyl tetrazolium chloride staining, and analyzed cardiac function by MRI and echocardiography.

RESULTS

 Transient LAD occlusions were found to increase EC proliferation and arteriole formation in the entire myocardium. These effects required β1 integrin on ECs, except for arteriole formation in the ischemic part of the myocardium. Furthermore, this integrin subunit was also relevant for basal and mechanically induced proliferation of human coronary artery ECs. Notably, β1 integrin was needed for cardioprotection induced by transient LAD occlusions, and the absence of endothelial β1 integrin resulted in impaired growth of blood vessels into the infarcted myocardium and reduced cardiac function after permanent LAD occlusion.

CONCLUSION

 We showed that endothelial β1 integrin is required for adaptation of the heart to cardiac ischemia and protection from myocardial infarction.

The relation between the atrial blood supply and the complexity of acute atrial fibrillation

Background

Patients with a history of myocardial infarction and coronary artery disease (CAD) have a higher risk of developing AF. Conversely, patients with atrial fibrillation (AF) have a higher risk of developing myocardial infarction, suggesting a link in underlying pathophysiology. The aim of this study was to assess whether coronary angiographic parameters are associated with a substrate for AF in patients without a history of AF.

Methods

During cardiac surgery in 62 patients (coronary artery bypass grafting (CABG;n = 47), aortic valve replacement (AVR;n = 9) or CABG + AVR (n = 6)) without a history of clinical AF (age 65.4 ± 8.5 years, 26.2% female), AF was induced by burst pacing. The preoperative coronary angiogram (CAG) was assessed for the severity of CAD, and the adequacy of atrial coronary blood supply as quantified by a novel scoring system including the location and severity of right coronary artery disease in relation to the right atrial branches. Epicardial mapping of the right atrium (256 unipolar electrodes) was used to assess the complexity of induced AF.

Results

There was no association between the adequacy of right atrial coronary blood supply on preoperative CAG and AF complexity parameters. Multivariable analysis revealed that only increasing age (B0.232 (0.030;0.433),p = 0.03) and the presence of 3VD (B3.602 (0.187;7.018),p = 0.04) were independently associated with an increased maximal activation time difference.

Conclusions

The adequacy of epicardial right atrial blood supply is not associated with increased complexity of induced atrial fibrillation in patients without a history of clinical AF, while age and the extent of ventricular coronary artery disease are.

Systemic immune inflammation index: a novel predictor for coronary collateral circulation

AIM

Recently, a new inflammatory and prognostic marker has emerged called as Systemic Immune Inflammation Index (SII). In the current study, we searched the relation between SII and Coronary Collateral Circulation (CCC) formation in stable Coronary Artery Disease (CAD).

MATERIALS & METHODS

449 patients with stable CAD who underwent coronary angiography and documented coronary stenosis of 95% or more in at least one major coronary vessel were included in the study. The study patients were divided into two groups according to the Rentrop score as well CCC (Rentrop 2-3) and bad CCC (Rentrop 0-1). Blood samples for SII and other laboratory parameters were gathered from all the patients on admission. The SII score was formulized as platelet × neutrophil/lymphocyte counts.

RESULTS

Patients, who had developed bad CCC had a higher C-reactive protein (CRP), neutrophil/lymphocyte ratio (NLR), platelets/lymphocyte ratio (PLR) and SII levels compared to those who had developed well CCC (p < 0.001, for all). Multivariate logistic regression analysis showed that high levels of SII was an independent predictor of bad CCC (OR: 1.005, 95% confidence interval (CI): 1.003-1.006, p < 0.001) together with dyslipidemia, high levels of CRP and NLR. In Receiver Operator Characteristic curve (ROC) analysis, the optimal cutoff value of SII to predict poor CCC was found to be 729.8, with 78.4% sensitivity and 74.6% specificity (area under ROC curve = 0.833 (95% CI: 0.777-0.889, p < 0.001).

CONCLUSION

We have demonstrated that SII, a novel cardiovascular risk marker, might be used as one of the independent predictors of CCC development.

Atorvastatin improves the proliferation and migration of endothelial progenitor cells via the miR-221/VEGFA axis

The present study was aimed at investigating the detailed functions of atorvastatin, a lipid-lowering agent, in the pathogenesis of coronary slow flow (CSF), a clinical disease characterized by delayed angiographic coronary opacity without obstructive coronary disease. In the present study, we successfully identified isolated endothelial progenitor cells (EPCs) from the peripheral blood of patients with CSF. Their vascular endothelial growth factor-A (VEGFA) protein levels were determined using immunoblotting analyses. We determined cell viability using MTT assays, cell migration capacity using Transwell assays, and the angiogenic capacity using a tube formation assay. The target association between miR-221 and VEGFA was validated with a luciferase reporter assay. Atorvastatin treatment increased EPC VEGFA protein levels, proliferation, migration, and angiogenesis. miR-221 expression was down-regulated after atorvastatin treatment; miR-221 overexpression exerted an opposing effect to atorvastatin treatment on VEGFA protein, EPC proliferation, migration, and angiogenesis. The protective effects of atorvastatin treatment on VEGFA protein and EPCs could be significantly suppressed by miR-221 overexpression. miR-221 directly bound the VEGFA 3'UTR to inhibit its expression. In conclusion, atorvastatin improves the cell proliferation, migration, and angiogenesis of EPCs via the miR-221/VEGFA axis. Thus, atorvastatin could be a potent agent against CSF, pending further in vivo and clinical investigations.

Cellular Senescence Affects Cardiac Regeneration and Repair in Ischemic Heart Disease

Ischemic heart disease (IHD) is defined as a syndrome of ischemic cardiomyopathy. Myogenesis and angiogenesis in the ischemic myocardium are important for cardiomyocyte (CM) survival, improving cardiac function and decreasing the progression of heart failure after IHD. Cellular senescence is a state of permanent irreversible cell cycle arrest caused by stress that results in a decline in cellular functions, such as proliferation, migration, homing, and differentiation. In addition, senescent cells produce the senescence-associated secretory phenotype (SASP), which affects the tissue microenvironment and surrounding cells by secreting proinflammatory cytokines, chemokines, growth factors, and extracellular matrix degradation proteins. The accumulation of cardiovascular-related senescent cells, including vascular endothelial cells (VECs), vascular smooth muscle cells (VSMCs), CMs and progenitor cells, is an important risk factor of cardiovascular diseases, such as vascular aging, atherosclerotic plaque formation, myocardial infarction (MI) and ventricular remodeling. This review summarizes the processes of angiogenesis, myogenesis and cellular senescence after IHD. In addition, this review focuses on the relationship between cellular senescence and cardiovascular disease and the mechanism of cellular senescence. Finally, we discuss a potential therapeutic strategy for MI targeting senescent cells.

A simple coronary blood flow model to study the collateral flow index

In this work, we present a novel modeling framework to investigate the effects of collateral circulation into the coronary blood flow physiology. A prototypical model of the coronary tree, integrated with the concept of Collateral Flow Index (CFI), is employed to gain insight about the role of model parameters associated with the collateral circuitry, which results in physically-realizable solutions for specific CFI data. Then, we discuss the mathematical feasibility of pressure-derived CFI, anatomical implications and practical considerations involving the estimation of model parameters in collateral connections. A sensitivity analysis is carried out, and the investigation of the impact of the collateral circulation on FFR values is also addressed.

Relationship Between C-Reactive Protein to Albumin Ratio and Coronary Collateral Circulation in Patients With Stable Coronary Artery Disease

We investigated the relationship between the C-reactive protein (CRP) to albumin ratio (CAR) and coronary collateral circulation (CCC) in stable coronary artery disease (CAD). Patients with stable CAD (n = 354) who underwent coronary angiography for suspected CAD and had a total occlusion ≥1 major coronary artery were included in the study. The participants were divided into 2 groups according to the Rentrop score as satisfactory CCC (Rentrop 2-3) and poor CCC (Rentrop 0-1). Patients who had poor CCC had a higher CRP, neutrophil/lymphocyte ratio (NLR), and CAR levels compared with those who had satisfactory CCC (P < .001, P = .046, P < .001, respectively). The CAR (odds ratio: 3.522, 95% CI: 2.515-4.932, P < .001), CRP, NLR, and diabetes mellitus were independent predictors of poor CCC. In receiver operator characteristic curve (ROC) analysis, the optimal cutoff value of CAR to predict poor CCC was 1.27 (area under ROC curve = 0.735 [95% CI: 0.667-0.803], P < .001). A raised CAR may be an independent predictor of poor CCC.

New Research Is Shining Light on How Collateral Arteries Form in the Heart: a Future Therapeutic Direction?

PURPOSE OF REVIEW

Collateral arteries create artery-artery anastomoses that could serve as natural bypasses that in the heart could relieve the various complications of ischemia heart disease. Recent work using animal models have begun to reveal details of how coronary collateral arteries form.

RECENT FINDINGS

Mouse genetics has been used to study the cellular and molecular mechanisms of collateral artery development. Collateral arteries are not pre-existing in the mouse heart, and only form in response to injury. Myocardial infarction creates tissue hypoxia that triggers the expression of growth factors and chemokines that guide collaterogenesis. Collateral development is more robust in neonatal hearts when compared with adults, and contributes to neonatal heart regeneration. The identification of signaling pathways and cellular responses underlying coronary collateral artery development suggests potential translational strategies. Continued investigation into this subject could lead to the identification of targetable pathways that induce collateral arteries for cardiac revascularization.

Visfatin and 25-Hydroxyvitamin D3 Levels Affect Coronary Collateral Circulation Development in Patients with Chronic Coronary Total Occlusion

Background: Coronary collateral circulation (CCC) plays a vital role in the myocardial blood supply, especially forischemic myocardium. Evidence suggests that the visfatin and 25-hydroxyvitamin D3 [25(OH)D3] levels are related to the degree and incidence of vascular stenosis associated with coronary artery disease; however, few studies have evaluated the effect of visfatin and 25(OH)D3 on CCC development in patients with chronic total occlusion (CTO).This study aimed to evaluate the relationship between the serum visfatin and 25(OH)D3 levels and CCC in patients with CTO.Methods: A total of 189 patients with CTO confirmed by coronary angiography were included. CCC was graded from 0 to 3 according to the Rentrop-Cohen classification. Patients with grade 0 or grade 1 collateral development were included in the poor CCC group (n = 82), whereas patients with grade 2 or grade 3 collateral development were included in the good CCC group (n = 107). The serum visfatin and 25(OH)D3 levels were measured by ELISA.Results: The visfatin level was significantly higher in the poor CCC group than in the good CCC group, and the 25(OH)D3 level was significantly lower in the poor CCC group than in the good CCC group (P = 0.000). Correlation analysis showed that the Rentrop grade was negatively correlated with the visfatin level (r = − 0.692, P = 0.000) but positively correlated with the 25(OH)D3 level (r = 0.635, P = 0.000). Logistic regression analysis showed that the visfatin and 25(OH)D3 levels were independent risk factors for CCC (odds ratio 1.597, 95% confidence interval 1.300–1.961, P = 0.000 and odds ratio 0.566, 95% confidence interval 0.444–0.722, P = 0.000, respectively). The visfatin and25(OH)D3 levels can effectively predict the CCC status.Conclusion: Serum visfatin and 25(OH)D3 levels are related to CCC development and are independent predictors of poor CCC.

Differential Regulation of mTOR Complexes with miR-302a Attenuates Myocardial Reperfusion Injury in Diabetes

Persistent activation of mTOR (mammalian target of rapamycin) in diabetes increases the vulnerability of the heart to ischemia/reperfusion (I/R) injury. We show here that infusion of rapamycin (mTOR inhibitor) at reperfusion following ischemia reduced myocardial infarct size and apoptosis with restoration of cardiac function in type 1 diabetic rabbits. Likewise, treatment with rapamycin protected hyperglycemic human-pluripotent-stem-cells-derived cardiomyocytes (HG-hiPSC-CMs) following simulated ischemia (SI) and reoxygenation (RO). Phosphorylation of S6 (mTORC1 marker) was increased, whereas AKT phosphorylation (mTORC2 marker) and microRNA-302a were reduced with concomitant increase of its target, PTEN, following I/R injury in diabetic heart and HG-hiPSC-CMs. Rapamycin inhibited mTORC1 and PTEN, but augmented mTORC2 with restoration of miRNA-302a under diabetic conditions. Inhibition of miRNA-302a blocked mTORC2 and abolished rapamycin-induced protection against SI/RO injury in HG-hiPSC-CMs. We conclude that rapamycin attenuates reperfusion injury in diabetic heart through inhibition of PTEN and mTORC1 with restoration of miR-302a-mTORC2 signaling.

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miR-302a and AKT phosphorylation are suppressed in post-ischemic diabetic heart

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Negative regulator of insulin signaling, PTEN, is induced after ischemia reperfusion

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miRNA-302a-mimic abolishes ischemic injury in hyperglycemic human iPS cardiocytes

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Rapamycin treatment restores miR-302a-mTORC2 cardioprotective signaling in diabetes

Association of fibrinogen/albumin ratio and coronary collateral circulation in stable coronary artery disease patients

Aim: To investigate whether fibrinogen/albumin ratio (FAR) has an association with the coronary collateral circulation (CCC) in patients with stable coronary artery disease. Materials & methods: A total of 391 patients with stable coronary artery disease who underwent coronary angiography were included. The patients were divided into two groups according to the Rentrop score. Results: The poorly developed CCC group had a significantly higher FAR level compared with the well-developed CCC group (p < 0.001). In the multivariate analysis, the FAR (odds ratio: 1.700; 95% CI: 1.420-2.036; p < 0.001) was an independent predictor of poorly developed CCC. Conclusion: FAR can be used as one of the independent predictors of CCC formation.

Incomplete protective effect of coronary collateral circulation for acute myocardial infarction patients

The short-term and long-term effects of coronary collateral circulation (CCC) discovered after acute myocardial infarction (AMI) are still debatable. This retrospective cohort study aimed to explore the clinical significance of CCC for AMI patients.A consecutive series of 323 AMI patients with CCC and 1339 AMI subjects without CCC were enrolled, most of them received percutaneous coronary intervention after AMI. Comparisons between CCC subjects and non-CCC population and between CCC sub-groups were applied regarded to basic clinical characteristics, stenosis extent indicated by Gensini score, myocardial infarction size estimated by peak concentration of troponin I (TnI), and left ventricular function evaluated by peak value of N-terminal pro-brain natriuretic peptide (NT-proBNP). Multiple linear regressions for NT-proBNP and TnI, and Kaplan-Meier curves for 5-years' main cardiovascular event (MACE) were also analyzed.CCC might provide incomplete protection by preventing excessive myocardial infarction but not a poorer heart function during AMI and CCC had no obvious protective effect on 5-years' MACE for AMI patients. More attentions should be paid to heart function for CCC patients during AMI.

Coronary Collateral Microcirculation Reserve Becomes Vestigial with Aging

INTRODUCTION

Our previous study indicated that coronary collateral microcirculation reserve (CCMR), native collaterals, transports blood flow to an ischemic area to reduce ischemic tissue injury. This study aimed to observe the changes of CCMR in the hearts of different month-old rats.

METHODS

We selected 2-, 8-, 16-, and 24-month-old rats as the research objects to monitor the changes of CCMR in rats with aging. After acute myocardial infarction, lectin-FITC was injected into the femoral vein vessels of rats to mark CCMR vessels in the ischemic area.

RESULTS

Results of the lectin-FITC perfusion experiment indicated that the number and collagen IV coverage of CCMR vessels declined with aging. Moreover, data suggested a correlation between endothelial nitric oxide synthase and a decline in the number of CCMR vessels.

CONCLUSION

Aging causes CCMR decline in rats.

Circulating CD34+VEGFR-2+ endothelial progenitor cells correlate with revascularization-mediated long-term improvement of cardiac function in patients with coronary chronic total occlusions

BACKGROUND

Endothelial progenitor cells (EPCs) participate in angiogenesis and neocollateralization. This study assessed if circulating EPCs can predict long-term improvement of global left ventricular systolic function in patients with coronary chronic total occlusions (CTOs) underwent successful percutaneous coronary intervention (PCI).

METHODS

In this single-center, prospective, observational study, 115 consecutive patients with CTOs were evaluated by standard transthoracic echocardiography (ECHO) before and 9-12 months after PCI. Numbers of circulating putative EPCs were determined by flow cytometry analysis of mononuclear cells isolated from peripheral blood samples drawn before and 72 h after PCI.

RESULTS

At mean 11.3 ± 2.5 months post vs. before PCI (all P < .05): by SAQ-7 summary scores, angina frequency, physical limitation and quality of life scores were greater; by ECHO, LVEDd decreased and LVEF increased, which were more significant in patients with Rentrop grades 2/3 vs. 0/1. At 72 h post vs. before PCI, CD34⁺VEGFR-2⁺CD133^- (0.82 ± 0.32 × 10⁶/L vs. 1.00 ± 0.39 × 10⁶/L, P = .003), CD34⁺VEGFR-2⁺CD133⁺ (0.24 ± 0.12 × 10⁶/L vs. 0.27 ± 0.14 × 10⁶/L, P = .028), and CD14⁺Tie2⁺VEGFR-2⁺ (6.60 ± 3.32 × 10⁶/L vs. 7.82 ± 3.91 × 10⁶/L, P = .006) cell numbers were lower. The baseline levels of CD34⁺VEGFR-2⁺cells (P = .001) and CD14⁺Tie2⁺VEGFR-2⁺cells (P < .001) were association with the grade of collateralization. In addition, the baseline and peri-procedural decrease of circulating CD34⁺VEGFR-2⁺ cells correlated with the increase of LVEF (P < .001, P < .001, respectively) and the decrease of LVEDd (P = .022, P = .029, respectively) at follow-up.

CONCLUSIONS

In this small study, the baseline levels of circulating CD34⁺VEGFR-2+ EPCs and its reduction after successful revascularization of CTOs correlated with long-term improvement in global LV systolic function.

Native Coronary Collateral Microcirculation Reserve in Rat Hearts

Background We occasionally noticed that native collateral blood flow showed a recessive trend in the early stages of acute myocardial infarction in rats, which greatly interferes with the accurate assessment of native collateral circulation levels. Here, we sought to recognize the coronary collateral circulation system in depth, especially the microcirculation part, on this basis. Methods and Results In this study, we detected native collateral flow with positron emission tomography perfusion imaging in rats and found that the native flow is relatively abundant when it is initially recruited. However, this flow is extremely unstable in the early stage of acute myocardial infarction and quickly fails. We used tracers to mark the collateral in an ischemic area and a massive preformed collateral network was labeled. The ultrastructures of these collateral microvessels are flawed, which contributes to extensive leakage and consequent interstitial edema in the ischemic region. Conclusions An unrecognized short-lived native coronary collateral microcirculation reserve is widely distributed in rat hearts. Recession of collateral blood flow transported by coronary collateral microcirculation reserve contributes to instability of native collateral blood flow in the early stage of acute myocardial infarction. The immature structure determines that these microvessels are short-lived and provide conditions for the development of early interstitial edema in acute myocardial infarction.

Exosomal CircHIPK3 Released from Hypoxia-Induced Cardiomyocytes Regulates Cardiac Angiogenesis after Myocardial Infarction

Exosomes play critical roles in mediating cell-to-cell communication by delivering noncoding RNAs (including miRNAs, lncRNAs, and circRNAs). Our previous study found that cardiomyocytes (CMs) subjected to hypoxia released circHIPK3-rich exosomes to regulate oxidative stress damage in cardiac endothelial cells. However, the role of exosomes in regulating angiogenesis after myocardial infarction (MI) remains unknown. The aim of this study was to establish the effects of exosomes derived from hypoxia-induced CMs on the migration and angiogenic tube formation of cardiac endothelial cells. Here, we reported that hypoxic exosomes (HPC-exos) can effectively reduce the infarct area and promote angiogenesis in the border surrounding the infarcted area. HPC-exos can also promote cardiac endothelial cell migration, proliferation, and tube formation in vitro. However, these effects were weakened after silencing circHIPK3 in hypoxia-induced CMs. We further verified that silencing and overexpressing circHIPK3 changed cardiac endothelial cell proliferation, migration, and tube formation in vitro by regulating the miR-29a expression. In addition, exosomal circHIPK3 derived from hypoxia-induced CMs first led to increased VEGFA expression by inhibiting miR-29a activity and then promoted accelerated cell cycle progression and proliferation in cardiac endothelial cells. Overexpression of miR-29a mimicked the effect of silencing circHIPK3 on cardiac endothelial cell activity in vitro. Thus, our study provides a novel mechanism by which exosomal circRNAs are involved in the communication between CMs and cardiac endothelial cells.

Correlation between ischemia-modified albumin level and coronary collateral circulation

OBJECTIVE

To investigate the correlation between ischemia-modified albumin (IMA) levels and coronary collateral circulation (CCC) in patients with chronic total occlusive (CTO).

METHODS

Coronary angiography was performed in the Department of Cardiology, Zhongnan Hospital of Wuhan University from 2017 to 08 to 2019-02 to identify 128 patients with CTO lesions in at least one major coronary artery. According to the Rentrop evaluation criteria, the degree of CCC formation was divided into the poor CCC formation group (Rentrop0-1 grade,n = 69) and the good CCC formation group (Rentrop2-3 grade,n = 59). The IMA level of the patients was measured using an albumin-cobalt binding assay. The general data, routine blood panel, total bilirubin (TBIL), blood lipids, uric acid (UA), left ventricular ejection fraction (LVEF) and other indicators of the patients were recorded and analyzed while assessing the patients' blood vessel occlusion.

RESULTS

The proportion of platelet count and diabetes in the poor CCC group was higher than that in the good CCC group (P < 0.05). The ratio of ischemia-modified albumin and total bilirubin in the poor CCC group was lower than that in the good CCC group (P < 0.05). Multivariate logistic regression analysis showed that ischemia-modified albumin was positively correlated with CCC formation [OR = 1.190,95% CI (1.092-1.297),P < 0.001], while diabetes was negatively correlated with CCC formation [OR = 0.285,95% CI (0.094-0.864), P < 0.05]. Ischemic modified albumin predicted good formation of CCC according to the ROC curve, and the area under the ROC curve was 0.769(95% CI,0.686-0.851, P<0.001); the optimal cut-off value was 63.35 KU/L, and the sensitivity was 71.2%,specificity is 71%.

CONCLUSION

The IMA level is closely related to good formation of CCC. Higher IMA levels can be used as an effective predictor of good CCC formation in patients with CTO.

Coronary vessel formation in development and disease: mechanisms and insights for therapy

The formation of new blood vessels after myocardial infarction (MI) is essential for the survival of existing and regenerated cardiac tissue. However, the extent of endogenous revascularization after MI is insufficient, and MI can often result in ventricular remodelling, progression to heart failure and premature death. The neutral results of numerous clinical trials that have evaluated the efficacy of angiogenic therapy to revascularize the infarcted heart reflect our poor understanding of the processes required to form a functional coronary vasculature. In this Review, we describe the latest advances in our understanding of the processes involved in coronary vessel formation, with mechanistic insights taken from developmental studies. Coronary vessels originate from multiple cellular sources during development and form through a number of distinct and carefully orchestrated processes. The ectopic reactivation of developmental programmes has been proposed as a new paradigm for regenerative medicine, therefore, a complete understanding of these processes is crucial. Furthermore, knowledge of how these processes differ between the embryonic and adult heart, and how they might be more closely recapitulated after injury are critical for our understanding of regenerative biology, and might facilitate the identification of tractable molecular targets to therapeutically promote neovascularization and regeneration of the infarcted heart.

Activation of CXCR7 alleviates cardiac insufficiency after myocardial infarction by promoting angiogenesis and reducing apoptosis

Angiogenesis is an important pathway for revascularization of ischemic tissues after acute myocardial infarction (AMI). It is unclear what role CXCR7 plays in angiogenesis in the ischemic area after AMI, although some researchers have shown that the activation of CXCR7 protectsthe heart under those conditions. Here, we hypothesize that the activation of CXCR7 promotes angiogenesis, reduces cell apoptosis and alleviates cardiac deficiency after AMI. C57BL/6 J mice were subjected to AMI and treated with TC14012 (10 mg/kg) for 24 days. HUVECs were cultured in a hypoxic (2% O₂) environment to generate a model of hypoxia. CXCR7 was knocked down in HUVECs by sh-CXCR7 transfection, and CXCR7 was activated by TC14012 (30 μM) treatment. The results showed that CXCR7 was downregulated in infarcted heart tissue and hypoxic HUVECs. The global activation of CXCR7 may alleviate the decrease in cardiac function indexes - (ejection fraction and fraction shortening), and reduce infarct size after AMI.. Moreover, CXCR7 activation has been shown to enhance the level of angiogenesis in ischemic heart tissue. In vitro, hypoxia-induced angiogenic functional loss and apoptosis are aggravated by CXCR7 knockdown in HUVECs. Both angiogenic impairment and cell apoptosis are rescued by CXCR7 activation. In conclusion, the present study indicates that activation of CXCR7 plays an important protective role for ischemic cells in hypoxic endothelial cells and AMI model mice by promoting angiogenesis and reducing apoptosis, which suggests that CXCR7 may be a potential therapeutic target to rescue the ischemic myocardium..

The Formation of Coronary Vessels in Cardiac Development and Disease

Understanding how coronary blood vessels form and regenerate during development and progression of cardiac diseases will shed light on the development of new treatment options targeting coronary artery diseases. Recent studies with the state-of-the-art technologies have identified novel origins of, as well as new, cellular and molecular mechanisms underlying the formation of coronary vessels in the postnatal heart, including collateral artery formation, endocardial-to-endothelial differentiation and mesenchymal-to-endothelial transition. These new mechanisms of coronary vessel formation and regeneration open up new possibilities targeting neovascularization for promoting cardiac repair and regeneration. Here, we highlight some recent studies on cellular mechanisms of coronary vessel formation, and discuss the potential impact and significance of the findings on basic research and clinical application for treating ischemic heart disease.

The Lipopeptide MALP-2 Promotes Collateral Growth

Beyond their role in pathogen recognition and the initiation of immune defense, Toll-like receptors (TLRs) are known to be involved in various vascular processes in health and disease. We investigated the potential of the lipopeptide and TLR2/6 ligand macrophage activating protein of 2-kDA (MALP-2) to promote blood flow recovery in mice. Hypercholesterolemic apolipoprotein E (Apoe)-deficient mice were subjected to microsurgical ligation of the femoral artery. MALP-2 significantly improved blood flow recovery at early time points (three and seven days), as assessed by repeated laser speckle imaging, and increased the growth of pre-existing collateral arteries in the upper hind limb, along with intimal endothelial cell proliferation in the collateral wall and pericollateral macrophage accumulation. In addition, MALP-2 increased capillary density in the lower hind limb. MALP-2 enhanced endothelial nitric oxide synthase (eNOS) phosphorylation and nitric oxide (NO) release from endothelial cells and improved the experimental vasorelaxation of mesenteric arteries ex vivo. In vitro, MALP-2 led to the up-regulated expression of major endothelial adhesion molecules as well as their leukocyte integrin receptors and consequently enhanced the endothelial adhesion of leukocytes. Using the experimental approach of femoral artery ligation (FAL), we achieved promising results with MALP-2 to promote peripheral blood flow recovery by collateral artery growth.

Visceral fat index: a novel predictor for coronary collateral circulation

Objective This study was designed to investigate the role of visceral adiposity along with other clinical parameters in predicting poor coronary collateral circulation (CCC) among patients with severe obstructive coronary artery disease (CAD). Subjects and methods A total of 135 patients with severe obstructive CAD and good (n = 70) or poor (n = 65) CCC were included. Data on angiographically detected CCC, the quality criteria for CCC (Rentrop scores) and visceral fat index (VFI) obtained via bioelectrical impedance were compared between good and poor CCC groups. Independent predictors of poor CCC, the correlation between VFI and Rentrop score and the role of VFI in the identification of CCC were analyzed. Results A significant negative correlation was noted between VFI and Rentrop scores (r = -0.668, < 0.001). The presence of hypertension (OR 4.244, 95% CI 1.184 to 15.211, p = 0.026) and higher VFI (OR 1.955, 95% CI 1.342 to 2.848, p < 0.001) were shown to be independent predictors of an increased risk for poor CCC. ROC analysis revealed a VFI > 9 (AUC [area under the curve] (95% CI): 0.898 (0.834-0.943), p < 0.0001) to be a potential predictor of poor CCC with a sensitivity of 95.38% and specificity of 85.71%. Conclusion In conclusion, our findings revealed comorbid hypertension and higher VFI to significantly predict the risk of poor CCC in patients with severe obstructive CAD.

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.

Effective myocardial perfusion and concomitant haemodynamic status determine the clinical diversity of anomalous left coronary artery from the pulmonary artery

BACKGROUND

Anomalous left coronary artery from the pulmonary artery is a rare congenital heart disease (CHD) with diverse clinical presentations despite the same anatomy. Factors determining this heterogeneous presentation are not well understood.

METHOD AND RESULTS

We retrospectively investigated 14 patients (12 females) who underwent surgical repair of anomalous left coronary artery from the pulmonary artery. These patients were divided into three groups based upon the severity of initial presentation: (1) severe, life-threatening condition (n = 5), (2) mild-to-moderate distress (n = 6), and (3) asymptomatic (n = 3). All patients presented with left ventricular dilation and retrograde flow in left coronary artery by echocardiogram. Eight patients in (1) and (2) presented with severe left ventricular dysfunction. All but one showed abnormal ECG consistent with myocardial ischemia or infarction. Asymptomatic patients had preserved left ventricular systolic function despite ischemic findings on ECG. In 13 patients after surgical repair, all but one normalised left ventricular geometry and systolic function, suggesting nearly full myocardial recovery upon improvement of myocardial perfusion; 8 patients had residual echogenic papillary muscle with variable degree of mitral regurgitation.

CONCLUSIONS

Evidence of myocardial ischemic injury was present in all patients with anomalous left coronary artery from the pulmonary artery regardless of their initial presentation. Retrograde flow in left coronary artery, implying collateral vessel development from right coronary artery to left coronary artery, was noted in all patients, yet only few patients had preserved systolic function at the time of diagnosis. The balance between effective myocardial perfusion and a deleterious fistulous flow provided by these collaterals and the simultaneous haemodynamic status are what determine the clinical diversity of anomalous left coronary artery from the pulmonary artery.

The Roles of AMPK in Revascularization

Coronary heart disease (CHD) is the most common and serious illness in the world and has been researched for many years. However, there are still no real effective ways to prevent and save patients with this disease. When patients present with myocardial infarction, the most important step is to recover ischemic prefusion, which usually is accomplished by coronary artery bypass surgery, coronary artery intervention (PCI), or coronary artery bypass grafting (CABG). These are invasive procedures, and patients with extensive lesions cannot tolerate surgery. It is, therefore, extremely urgent to search for a noninvasive way to save ischemic myocardium. After suffering from ischemia, cardiac or skeletal muscle can partly recover blood flow through angiogenesis (de novo capillary) induced by hypoxia, arteriogenesis, or collateral growth (opening and remodeling of arterioles) triggered by dramatical increase of fluid shear stress (FSS). Evidence has shown that both of them are regulated by various crossed pathways, such as hypoxia-related pathways, cellular metabolism remodeling, inflammatory cells invasion and infiltration, or hemodynamical changes within the vascular wall, but still they do not find effective target for regulating revascularization at present. 5′-Adenosine monophosphate-activated protein kinase (AMPK), as a kinase, is not only an energy modulator but also a sensor of cellular oxygen-reduction substances, and many researches have suggested that AMPK plays an essential role in revascularization but the mechanism is not completely understood. Usually, AMPK can be activated by ADP or AMP, upstream kinases or other cytokines, and pharmacological agents, and then it phosphorylates key molecules that are involved in energy metabolism, autophagy, anti-inflammation, oxidative stress, and aging process to keep cellular homeostasis and finally keeps cell normal activity and function. This review makes a summary on the subunits, activation and downstream targets of AMPK, the mechanism of revascularization, the effects of AMPK in endothelial cells, angiogenesis, and arteriogenesis along with some prospects.

Arteriogenesis of the Spinal Cord-The Network Challenge

Spinal cord ischemia (SCI) is a clinical complication following aortic repair that significantly impairs the quality and expectancy of life. Despite some strategies, like cerebrospinal fluid drainage, the occurrence of neurological symptoms, such as paraplegia and paraparesis, remains unpredictable. Beside the major blood supply through conduit arteries, a huge collateral network protects the central nervous system from ischemia—the paraspinous and the intraspinal compartment. The intraspinal arcades maintain perfusion pressure following a sudden inflow interruption, whereas the paraspinal system first needs to undergo arteriogenesis to ensure sufficient blood supply after an acute ischemic insult. The so-called steal phenomenon can even worsen the postoperative situation by causing the hypoperfusion of the spine when, shortly after thoracoabdominal aortic aneurysm (TAAA) surgery, muscles connected with the network divert blood and cause additional stress. Vessels are a conglomeration of different cell types involved in adapting to stress, like endothelial cells, smooth muscle cells, and pericytes. This adaption to stress is subdivided in three phases—initiation, growth, and the maturation phase. In fields of endovascular aortic aneurysm repair, pre-operative selective segmental artery occlusion may enable the development of a sufficient collateral network by stimulating collateral vessel growth, which, again, may prevent spinal cord ischemia. Among others, the major signaling pathways include the phosphoinositide 3 kinase (PI3K) pathway/the antiapoptotic kinase (AKT) pathway/the endothelial nitric oxide synthase (eNOS) pathway, the Erk1, the delta-like ligand (DII), the jagged (Jag)/NOTCH pathway, and the midkine regulatory cytokine signaling pathways.

PCI and CABG for Treating Stable Coronary Artery Disease: JACC Review Topic of the Week

Percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG) are considered revascularization procedures, but only CABG can prolong life in stable coronary artery disease. Thus, PCI and CABG mechanisms may differ. Viability and/or ischemia detection to guide revascularization have been unable to accurately predict treatment effects of CABG or PCI, questioning a revascularization mechanism for improving survival. By contrast, preventing myocardial infarction may save lives. However, the majority of infarcts are generated by non-flow-limiting stenoses, but PCI is solely focused on treating flow-limiting lesions. Thus, PCI cannot be expected to significantly limit new infarcts, but CABG may do so through providing flow distal to vessel occlusions. All comparisons of CABG to PCI or medical therapy that demonstrate survival effects with CABG also demonstrate infarct reduction. Thus, CABG may differ from PCI by providing "surgical collateralization," prolonging life by preventing myocardial infarctions. The evidence is reviewed here.

The association between serum angiogenin and osteopontin levels and coronary collateral circulation in patients with chronic total occlusion

OBJECTIVE

A well-developed coronary collateral circulation lowers both in-hospital and long-term morbidity and mortality limiting the infarct. Angiogenin (AGN) and osteopontin (OPN) are known to be potent inducers of angiogenesis. The aim of the present study was to investigate the relationship between serum ANG and OPN levels and collateral filling grade in subjects with stable coronary artery disease (SCAD).

METHODS

A total of 122 age- and gender-matched consecutive patients who were found to have total occlusion (n=70) and no significant stenosis in epicardial coronary arteries (n=52) who underwent coronary angiography due to SCAD between January 2015 and July 2017 were included in the study. AGN and OPN levels were measured using enzyme linked immunosorbent assay. Coronary collateral circulation was graded using Rentrop's classification of collateral filling.

RESULTS

A total of 52 patients (61.60±11.78 years, 61.5% male) without significant epicardial coronary artery stenosis and 70 patients (62.87±8.24 years, 65.7% male) with totally occluded coronary arteries were included in the study. Subjects with total occlusion had significantly higher levels of AGN [122.00 (79.00-623.00) pg/mL vs. 98.00 (18.00-160.00) pg/mL, p<0.001] and OPN [1863.50 (125.00-6500.00) pg/mL vs. 451.00 (112.00- 1850.00) pg/mL, p<0.001] than those without significant stenosis. In addition, AGN [127.00 (87.00-623.00) pg/mL vs. 110.00 (79.00-188.00) pg/mL, p=0.011] and OPN [2681.00 (126.00-6500.00) pg/mL vs. 649.00 (125.00-4255.00) pg/mL, p=0.001] levels were significantly higher in patients with better developed collaterals. Serum AGN and OPN levels were found to be significantly associated with coronary collateral development.

CONCLUSION

AGN and OPN are associated with better developed coronary collateral circulation and may have therapeutic implications for the promotion of coronary collateral development.

Exosomal circHIPK3 Released from Hypoxia-Pretreated Cardiomyocytes Regulates Oxidative Damage in Cardiac Microvascular Endothelial Cells via the miR-29a/IGF-1 Pathway

Background/Aims

Circular RNAs (circRNAs) are a class of endogenous noncoding RNAs that regulate gene expression in eukaryotes. Recently, exosomes from cardiomyocytes (CMs) have been found to facilitate cell proliferation and survival by transporting various bioactive molecules, including circRNA. However, the functions of exosomal circRNAs are not clear. The present research is aimed at determining whether circHIPK3 released from hypoxia-pretreated CMs is transferred into cardiac microvascular endothelial cells (CMVECs) by exosomes and becomes functionally active in the CMVECs under oxidative stress conditions.

Methods

Quantitative polymerase chain reactions were conducted to detect the expression pattern of circHIPK3 in CMVECs under oxidative stress. Annexin V-FITC/propidium iodide (PI) staining assays, TUNEL assays, ROS assays, and Western blot analysis were conducted to detect the role of exosomal circHIPK3 in CMVEC function in vitro. Luciferase activity assays and RNA immunoprecipitation studies were conducted in vitro to reveal the mechanism of circHIPK3-mediated CMVEC function.

Results

circHIPK3 expression was significantly upregulated in hypoxic exosomes (HPC-exos) compared with normoxic exosomes (Nor-exos). Moreover, HPC-exos induced stronger antioxidant effects than Nor-exos. The silencing or overexpression of circHIPK3 changed CMVEC survival under oxidative conditions in vitro. Furthermore, circHIPK3 silencing in HPC-exos abrogated the protective effects of HPC-exos in CMVECs, as shown by increased levels of apoptosis, ROS, MDA, and proapoptotic proteins. circHIPK3 acted as an endogenous miR-29a sponge to sequester and inhibit miR-29a activity, which led to increased IGF-1 expression. The ectopic expression of miR-29a mimicked the effect of circHIPK3 silencing in CMVECs in vitro.

Conclusions

circHIPK3 in HPC-exos plays a role in CMVECs under oxidative conditions through miR-29a-mediated IGF-1 expression, leading to a decrease in oxidative stress-induced CMVECs dysfunction. These data suggest that the exosomal circRNA in CMs is a potential target to control CMVECs dysfunction under oxidative conditions.

Debates over NICE Guideline Update: What Are the Roles of Nuclear Cardiology in the Initial Evaluation of Stable Chest Pain?

Recent clinical trials have demonstrated the values of cardiac computed tomography (CT) in the initial evaluation of stable chest pain which led to drastic changes in the National Institute for Health and Care Excellence (NICE) guidelines in 2016. According to the updated NICE guidelines, cardiac CT should be performed as the initial cardiac testing in stable chest pain regardless of pre-test probability (PTP) of coronary artery disease (CAD). As a result, cardiac CT is now considered as a validated gatekeeper for assessing stable chest pain, which precedes all the functional studies including nuclear myocardial perfusion imaging (MPI). Nuclear MPI, in contrast, has been assigned as one of the second-line studies, which is inevitably dependent on the results of cardiac CT. However, nuclear MPI has genuine values in the diagnosis, treatment decision, and prognostic stratification of stable chest pain, which cannot be replaced by cardiac CT. In this review, the updated NICE guidelines and related cardiac CT trials will be critically reviewed from the view of nuclear physicians and the exceptional values of nuclear MPI will be described along with the future perspectives.

Pigment Epithelium-Derived Factor Increases Native Collateral Blood Flow to Improve Cardiac Function and Induce Ventricular Remodeling After Acute Myocardial Infarction

Background

We previously found that the structural defects of the coronary collateral microcirculation reserve (CCMR) prevent these preformed collateral vessels from continuously delivering the native collateral blood and supporting the ischemic myocardium in rats. Here, we tested whether these native collaterals can be remodeled by artificially increasing pigment epithelium–derived factor (PEDF) expression and demonstrated the mechanism for this stimulation.

Methods and Results

We performed intramyocardial gene delivery (PEDF‐lentivirus, 2×10⁷ TU) along the left anterior descending coronary artery to artificially increase the expression of PEDF in the tissue of the region for 2 weeks. By blocking the left anterior descending coronary artery, we examined the effects of PEDF on native collateral blood flow and CCMR. The results of positron emission tomography perfusion imaging showed that PEDF increased the native collateral blood flow and significantly inhibited its decline during acute myocardial infarction. In addition, the number of CCMR vessels decreased and the size increased. Similar results were obtained from in vitro experiments. We tested whether PEDF induces CCMR remodeling in a fluid shear stress–like manner by detecting proteins and signaling pathways that are closely related to fluid shear stress. The nitric oxide pathway and the Notch‐1 pathway participated in the process of CCMR remodeling induced by PEDF.

Conclusions

PEDF treatment activates the nitric oxide pathway, and the Notch‐1 pathway enabled CCMR remodeling. Increasing the native collateral blood flow can promote the ventricular remodeling process and improve prognosis after acute myocardial infarction.

Ventricular Arrhythmias in First Acute Myocardial Infarction: Epidemiology, Mechanisms, and Interventions in Large Animal Models

Ventricular arrhythmia and subsequent sudden cardiac death (SCD) due to acute myocardial infarction (AMI) is one of the most frequent causes of death in humans. Lethal ventricular arrhythmias like ventricular fibrillation (VF) prior to hospitalization have been reported to occur in more than 10% of all AMI cases and survival in these patients is poor. Identification of risk factors and mechanisms for VF following AMI as well as implementing new risk stratification models and therapeutic approaches is therefore an important step to reduce mortality in people with high cardiovascular risk. Studying spontaneous VF following AMI in humans is challenging as it often occurs unexpectedly in a low risk subgroup. Large animal models of AMI can help to bridge this knowledge gap and are utilized to investigate occurrence of arrhythmias, involved mechanisms and therapeutic options. Comparable anatomy and physiology allow for this translational approach. Through experimental focus, using state-of-the-art technologies, including refined electrical mapping equipment and novel pharmacological investigations, valuable insights into arrhythmia mechanisms and possible interventions for arrhythmia-induced SCD during the early phase of AMI are now beginning to emerge. This review describes large experimental animal models of AMI with focus on first AMI-associated ventricular arrhythmias. In this context, epidemiology of first AMI, arrhythmogenic mechanisms and various potential therapeutic pharmacological targets will be discussed.

Stimulation of Collateral Vessel Growth by Inhibition of Galectin 2 in Mice Using a Single-Domain Llama-Derived Antibody

Background

In the presence of arterial stenosis, collateral artery growth (arteriogenesis) can alleviate ischemia and preserve tissue function. In patients with poorly developed collateral arteries, Gal‐2 (galectin 2) expression is increased. In vivo administration of Gal‐2 inhibits arteriogenesis. Blocking of Gal‐2 potentially stimulates arteriogenesis. This study aims to investigate the effect of Gal‐2 inhibition on arteriogenesis and macrophage polarization using specific single‐domain antibodies.

Methods and Results

Llamas were immunized with Gal‐2 to develop anti–Gal‐2 antibodies. Binding of Gal‐2 to monocytes and binding inhibition of antibodies were quantified. To test arteriogenesis in vivo, Western diet‐fed LDLR.(low‐density lipoprotein receptor)–null Leiden mice underwent femoral artery ligation and received treatment with llama antibodies 2H8 or 2C10 or with vehicle. Perfusion restoration was measured with laser Doppler imaging. In the hind limb, arterioles and macrophage subtypes were characterized by histology, together with aortic atherosclerosis. Llama‐derived antibodies 2H8 and 2C10 strongly inhibited the binding of Gal‐2 to monocytes (93% and 99%, respectively). Treatment with these antibodies significantly increased perfusion restoration at 14 days (relative to sham, vehicle: 41.3±2.7%; 2H8: 53.1±3.4%, P=0.016; 2C10: 52.0±3.8%, P=0.049). In mice treated with 2H8 or 2C10, the mean arteriolar diameter was larger compared with control (vehicle: 17.25±4.97 μm; 2H8: 17.71±5.01 μm; 2C10: 17.84±4.98 μm; P<0.001). Perivascular macrophages showed a higher fraction of the M2 phenotype in both antibody‐treated animals (vehicle: 0.49±0.24; 2H8: 0.73±0.15, P=0.007; 2C10: 0.75±0.18, P=0.006). In vitro antibody treatment decreased the expression of M1‐associated cytokines compared with control (P<0.05 for each). Atherosclerotic lesion size was comparable between groups (overall P=0.59).

Conclusions

Inhibition of Gal‐2 induces a proarteriogenic M2 phenotype in macrophages, improves collateral artery growth, and increases perfusion restoration in a murine hind limb model.

A noninvasive and highly sensitive approach for the assessment of coronary collateral circulation by 192-slice third-generation dual-source computed tomography

The coronary collateral circulation (CCC) is an alternative source of blood supply when the original vessels fail to provide sufficient blood. The accurate detection of CCC is critical for the treatment of ischemic heart disease, especially when the stent surgery is not an option. The assessment of minute vessels such as coronary collateral arteries is challenging. The objective of this study was to assess the feasibility of detection and classification of CCC using the192-slice third-generation dual-source computed tomography angiography (192-slice DSCT CTA).Eight hundred patients (450 men and 350 women, mean age: 56 ± 11 years) with complete or subtotal occlusion of at least 1 major coronary artery were enrolled for our study. February 2016 and September 2018, the patient both 192-slice DSCT CTA and conventional coronary angiography (CAG) were performed in all enrolled patients. The interval between two approaches for a given patient was 6.1 ± 3.7 days (Range: 1-15). The diagnostic accuracy of 192-slice DSCT CTA was evaluated by comparing it with that of CAG. The identified CCC was graded according to the Rentrop classification.The prevalence among patients of having at least 1 CCC was 43.8%. The sensitivity for detecting CCC by 192-slice DSCT was 91.7% (95% CI: 88.3% to 94.3%), specificity was 95.5% (95% CI: 93.1% to 97.2%), positive predictive value was 94.3% (95% CI: 91.5% to 96.2%), and negative predictive value was 93.3% (95% CI: 90.9% to 95.3%). Cohen-Kappa analysis showed that the consistency of the correct classification of CCC using CAG and 192-slice DSCT was very high with the kappa coefficient (κ) of 0.94 (95% CI: 0.91-0.96, P value = .01). Additionally, the radiation dose for 192-slice DSCT was as low as 0.42 ± 0.04 mSv (range, 0.35-0.43 mSv).The 192-slice DSCT CTA is a reliable and sensitive non-invasive method for the evaluation of CCC with low radiation doses.

Exercise Training as a Mediator for Enhancing Coronary Collateral Circulation: A Review of the Evidence

Coronary collateral vessels supply blood to areas of myocardium at risk after arterial occlusion. Flow through these channels is driven by a pressure gradient between the donor and the occluded artery. Concomitant with increased collateral flow is an increase in shear force, a potent stimulus for collateral development (arteriogenesis). Arteriogenesis is self-limiting, often ceasing prematurely when the pressure gradient is reduced by the expanding lumen of the collateral vessel. After the collateral has reached its self-limited maximal conductance, the only way to drive further increases is to re-establish the pressure gradient.

During exercise, the myocardial oxygen demand is increased, subsequently increasing coronary flow. Therefore, exercise may represent a means of driving augmented arteriogenesis in patients with stable coronary artery disease. Studies investigating the ability of exercise to drive collateral development in humans are inconsistent. However, these inconsistencies may be due to the heterogeneity of assessment methods used to quantify change. This article summarises current evidence pertaining to the role of exercise in the development of coronary collaterals, highlighting areas of future research.

The Human Coronary Collateral Circulation, Its Extracardiac Anastomoses and Their Therapeutic Promotion

Cardiovascular disease remains the leading global cause of death, and the number of patients with coronary artery disease (CAD) and exhausted therapeutic options (i.e., percutaneous coronary intervention (PCI), coronary artery bypass grafting (CABG) and medical treatment) is on the rise. Therefore, the evaluation of new therapeutic approaches to offer an alternative treatment strategy for these patients is necessary. A promising research field is the promotion of the coronary collateral circulation, an arterio-arterial network able to prevent or reduce myocardial ischemia in CAD. This review summarizes the basic principles of the human coronary collateral circulation, its extracardiac anastomoses as well as the different therapeutic approaches, especially that of stimulating the extracardiac collateral circulation via permanent occlusion of the internal mammary arteries.

Collateral Vessels Have Unique Endothelial and Smooth Muscle Cell Phenotypes

Collaterals are unique blood vessels present in the microcirculation of most tissues that, by cross-connecting a small fraction of the outer branches of adjacent arterial trees, provide alternate routes of perfusion. However, collaterals are especially susceptible to rarefaction caused by aging, other vascular risk factors, and mouse models of Alzheimer’s disease—a vulnerability attributed to the disturbed hemodynamic environment in the watershed regions where they reside. We examined the hypothesis that endothelial and smooth muscle cells (ECs and SMCs, respectively) of collaterals have specializations, distinct from those of similarly-sized nearby distal-most arterioles (DMAs) that maintain collateral integrity despite their continuous exposure to low and oscillatory/disturbed shear stress, high wall stress, and low blood oxygen. Examination of mouse brain revealed the following: Unlike the pro-inflammatory cobble-stoned morphology of ECs exposed to low/oscillatory shear stress elsewhere in the vasculature, collateral ECs are aligned with the vessel axis. Primary cilia, which sense shear stress, are present, unexpectedly, on ECs of collaterals and DMAs but are less abundant on collaterals. Unlike DMAs, collaterals are continuously invested with SMCs, have increased expression of Pycard, Ki67, Pdgfb, Angpt2, Dll4, Ephrinb2, and eNOS, and maintain expression of Klf2/4. Collaterals lack tortuosity when first formed during development, but tortuosity becomes evident within days after birth, progresses through middle age, and then declines—results consistent with the concept that collateral wall cells have a higher turnover rate than DMAs that favors proliferative senescence and collateral rarefaction. In conclusion, endothelial and SMCs of collaterals have morphologic and functional differences from those of nearby similarly sized arterioles. Future studies are required to determine if they represent specializations that counterbalance the disturbed hemodynamic, pro-inflammatory, and pro-proliferative environment in which collaterals reside and thus mitigate their risk factor-induced rarefaction.

Lipoprotein (a) interactions with cholesterol-containing lipids on angiographic coronary collateralization in type 2 diabetic patients with chronic total occlusion

Background

We investigated whether or to what extent the interaction of lipoprotein (a) [Lp(a)] with cholesterol-containing lipids was associated with angiographic coronary collateralization in type 2 diabetic patients with chronic total occlusion.

Methods

Serum levels of Lp(a), total cholesterol, low-density lipoprotein–cholesterol (LDL-C), high-density lipoprotein–cholesterol (HDL-C), and triglyceride were determined and non-HDL-C was calculated in 706 type 2 diabetic and 578 non-diabetic patients with stable coronary artery disease and angiographic total occlusion of at least one major coronary artery. The degree of collaterals supplying the distal aspect of a total occlusion from the contra-lateral vessel was graded as poor (Rentrop score of 0 or 1) or good coronary collateralization (Rentrop score of 2 or 3).

Results

For diabetic and non-diabetic patients, Lp(a), total cholesterol, LDL-C, and non-HDL-C levels were higher in patients with poor coronary collateralization than in those with good collateralization, whereas HDL-C and triglyceride levels were similar. After adjustment for potential confounding factors, tertiles of Lp(a), total cholesterol, LDL-C and non-HDL-C remained independent determinants for poor collateralization. A significant interaction between Lp(a) and total cholesterol, LDL-C or non-HDL-C was observed in diabetic patients (all P interaction < 0.001) but not in non-diabetics. At high tertile of total cholesterol (≥ 5.35 mmol/L), LDL-C (≥ 3.36 mmol/L) and non-HDL-C (≥ 4.38 mmol/L), diabetic patients with high tertile of Lp(a) (≥ 30.23 mg/dL) had an increased risk of poor collateralization compared with those with low tertile of Lp(a) (< 12.66 mg/dL) (adjusted OR = 4.300, 3.970 and 4.386, respectively, all P < 0.001).

Conclusions

Increased Lp(a) confers greater risk for poor coronary collateralization when total cholesterol, LDL-C or non-HDL-C are elevated especially for patients with type 2 diabetes.

Electronic supplementary material

The online version of this article (10.1186/s12933-019-0888-z) contains supplementary material, which is available to authorized users.

Noninvasive Recanalization of a Coronary Chronic Total Occlusion

BACKGROUND

Spontaneous recanalization of a chronically occluded artery is rare and reported anecdotally.

CASE SUMMARY

We report a case of a patient with a chronically occluded right coronary artery, found on a coronary angiography performed due to acute ST elevation myocardial infarction with an occluded circumflex artery as a culprit lesion. Three months later, a follow-up angiography was performed and a recanalization of the occluded right coronary artery was detected.

DISCUSSION

There is a possibility that intrinsic fibrinolytic mechanisms with the additional effect of standard antithrombotic drugs administrated after the acute coronary event led to the recanalization.

The dynamics of monocytes in the process of collateralization

Collateralization is an important way for patients with coronary heart disease to supply blood flow to the ischemic area. At present, research on the mechanism of collateral circulation mainly focuses on the inflammatory response. Monocytes are the kernel of inflammatory response during arteriogenesis. Therefore, we reviewed the recent developments in this field in terms of the dynamic changes of monocytes during collateralization. We searched and scanned PubMed for the following terms until November 2018: collateral, collateralization, monocyte, macrophage, and arteriogenesis. Articles were obtained and examined to figure out the dynamics of monocytes in the progress of collateralization. Substantial research shows that recruitment, infiltration, and phenotypic transformation of monocytes can affect function in various ways, respectively. Mechanical or chemical factors that can produce effects on collateral development may be due partly to impact on dynamics of monocytes. Although mechanisms of dynamics of monocytes during arteriogenesis are not elucidated clearly, there is no doubt that deeper exploration of the underlying mechanisms will contribute to pharmaceutical development aiming for promoting collateral development.

Polycythemia Vera Presenting as Cardiac Arrest: Novel Management Strategies

Acute coronary syndromes (ACS) usually occur in patients with multiple cardiac risk factors. In young adults, drug use and hypercoagulable states are common causes for ACS presentations. We report a case of a man in his early 30s who was diagnosed with polycythemia vera (PV) and had a cardiac arrest due to an anterolateral ST elevation myocardial infarction. We discuss his unique management and review the evidence on the management of arterial thromboembolism in PV patients.

A Unique Collateral Artery Development Program Promotes Neonatal Heart Regeneration

Collateral arteries are an uncommon vessel subtype that can provide alternate blood flow to preserve tissue following vascular occlusion. Some patients with heart disease develop collateral coronary arteries, and this correlates with increased survival. However, it is not known how these collaterals develop or how to stimulate them. We demonstrate that neonatal mouse hearts use a novel mechanism to build collateral arteries in response to injury. Arterial endothelial cells (ECs) migrated away from arteries along existing capillaries and reassembled into collateral arteries, which we termed "artery reassembly". Artery ECs expressed CXCR4, and following injury, capillary ECs induced its ligand, CXCL12. CXCL12 or CXCR4 deletion impaired collateral artery formation and neonatal heart regeneration. Artery reassembly was nearly absent in adults but was induced by exogenous CXCL12. Thus, understanding neonatal regenerative mechanisms can identify pathways that restore these processes in adults and identify potentially translatable therapeutic strategies for ischemic heart disease.

Cardiovascular drugs attenuated myocardial resistance against ischaemia-induced and reperfusion-induced injury in a rat model of repetitive occlusion

Objective

We investigated the impact of cardioprotective drugs on ST-elevation, arrhythmias and infarct size in a rat model of repetitive coronary artery occlusion.

Methods

Seventy Sprague-Dawley rats were randomised to two control and five treatment groups. Placebo was either implantation of a pneumatic occluder onto the left anterior descending coronary artery (LAD) without starting repetitive occlusion (SHAM) or subsequent RO of the LAD over 10 days without medication (ROP). Treatment groups underwent RO and additionally received nitroglycerin (NTG), metoprolol, verapamil (VER), ranolazine (RAN) or candesartan (CAN). Two weeks after the intervention, rats underwent a single, sustained LAD occlusion followed by reperfusion. To evaluate differences in cardiac resistance against myocardial ischaemia and reperfusion injury, cardiac surrogate parameters including maximal ST-elevation, arrhythmias and infarct size were assessed.

Results

Compared with sham, RO alone and RO plus nitroglycerin were associated with significantly lower maximal ST-elevation and percentage of infarcted myocardium (SHAM 0.12 mV, ROP 0.06 mV (p=0.004), NTG 0.05 mV (p=0.005); SHAM 16.2%, ROP 6.6% (p=0.008), NTG 5.9% (p=0.006). Compared with RO alone, RO plus RAN was accompanied by increased ST-elevation (0.13 mV, p=0.018) and RO plusVER or CAN by more infarcted myocardium (14.2%, p=0.004% and 15.5%, p=0.003, respectively). Rats treated with VER, RAN or CAN tended to severe arrhythmias more frequently than those of the control groups.

Conclusions

RO led to an increased myocardial resistance against ischaemia and reperfusion injury. Concomitant administration of nitroglycerin did not affect the efficacy of RO. Cardiovascular channel or receptor blockers reduced the efficacy of RO.

Cardioprotection during ischemia by coronary collateral growth

Ischemic heart diseases (IHD) cause millions of deaths around the world annually. While surgical and pharmacological interventions are commonly used to treat patients with IHD, their efficacy varies from patient to patient and is limited by the severity of the disease. One promising, at least theoretically, approach for treating IHD is induction of coronary collateral growth (CCG). Coronary collaterals are arteriole-to-arteriole anastomoses that can undergo expansion and remodeling in the setting of coronary disease when the disease elicits myocardial ischemia and creates a pressure difference across the collateral vessel that creates unidirectional flow. Well-developed collaterals can restore blood flow in the ischemic area of the myocardium and protect the myocardium at risk. Moreover, such collaterals are correlated to reduced mortality and infarct size and better cardiac function during occlusion of coronary arteries. Therefore, understanding the process of CCG is highly important as a potentially viable treatment of IHD. While there are several excellent review articles on this topic, this review will provide a unified overview of the various aspects related to CCG as well as an update of the advancements in the field. We also call for more detailed studies with an interdisciplinary approach to advance our knowledge of CCG. In this review, we will describe growth of coronary collaterals, the various factors that contribute to CCG, animal models used to study CCG, and the cardioprotective effects of coronary collaterals during ischemia. We will also discuss the impairment of CCG in metabolic syndrome and the therapeutic potentials of CCG in IHD.