Stimulation of coronary collateral growth by granulocyte stimulating factor: role of reactive oxygen species

Angiotensin receptor-neprilysin inhibitor improves coronary collateral perfusion

Background

We investigated the pleiotropic effects of an angiotensin receptor-neprilysin inhibitor (ARNi) on collateral-dependent myocardial perfusion in a rat model of coronary arteriogenesis, and performed comprehensive analyses to uncover the underlying molecular mechanisms.

Methods

A rat model of coronary arteriogenesis was established by implanting an inflatable occluder on the left anterior descending coronary artery followed by a 7-day repetitive occlusion procedure (ROP). Coronary collateral perfusion was measured by using a myocardial particle infusion technique. The putative ARNi-induced pro-arteriogenic effects were further investigated and compared with an angiotensin-converting enzyme inhibitor (ACEi). Expression of the membrane receptors and key enzymes in the natriuretic peptide system (NPS), renin-angiotensin-aldosterone system (RAAS) and kallikrein-kinin system (KKS) were analyzed by quantitative polymerase chain reaction (qPCR) and immunoblot assay, respectively. Protein levels of pro-arteriogenic cytokines were measured by enzyme-linked immunosorbent assay, and mitochondrial DNA copy number was assessed by qPCR due to their roles in arteriogenesis. Furthermore, murine heart endothelial cells (MHEC5-T) were treated with a neprilysin inhibitor (NEPi) alone, or in combination with bradykinin receptor antagonists. MHEC5-T proliferation was analyzed by colorimetric assay.

Results

The in vivo study showed that ARNis markedly improved coronary collateral perfusion, regulated the gene expression of KKS, and increased the concentrations of relevant pro-arteriogenic cytokines. The in vitro study demonstrated that NEPis significantly promoted MHEC5-T proliferation, which was diminished by bradykinin receptor antagonists.

Conclusion

ARNis improve coronary collateral perfusion and exert pro-arteriogenic effects via the bradykinin receptor signaling pathway.

Angiotensin-converting enzyme inhibitors stimulate cerebral arteriogenesis

AIM

Arteriogenesis constitutes the most efficient endogenous rescue mechanism in cases of cerebral ischaemia. The aim of this work was to investigate whether angiotensin-converting enzyme inhibitors (ACEi) stimulates, and angiotensin II receptor type 1 blockers (ARB) inhibits cerebral collateral growth by applying a three-vessel occlusion (3-VO) model in rat.

METHODS

Cerebral collateral growth was measured post 3-VO (1) by assessing blood flow using the cerebrovascular reserve capacity (CVRC) technique, and (2) by assessing vessel diameters in the posterior cerebral artery (PCA) via the evaluation of latex angiographies. A stimulatory effect on arteriogenesis was investigated for ACEi administration ± bradykinin receptor 1 (B1R) and 2 (B2R) blockers, and an inhibitory effect was analysed for ARB administration. Results were validated by immunohistochemical analysis and mechanistic data were collected by human umbilical vein endothelial cell (HUVEC) viability or scratch assay and monocyte (THP-1) migration assay.

RESULTS

An inhibitory effect of ARB on arteriogenesis could not be demonstrated. However, collateral growth measurements demonstrated a significantly increased CVRC and PCA diameters in the ACEi group. ACEi stimulates cell viability and migration, which could be partially reduced by additional administration of bradykinin receptor 1 inhibitor (B1Ri). ACEi inhibits the degradation of pro-arteriogenic bradykinin derivatives, but combined ACEi + B1Ri + B1Ri (BRB) treatment did not reverse the stimulatory effect. Yet, co-administration of ACEi + BRB enhances arteriogenesis and cell migration.

CONCLUSION

We demonstrate a potent stimulatory effect of ACEi on cerebral arteriogenesis in rats, presumable via B1R. However, results imply a pleiotropic and compensatory effect of ACEi on bradykinin receptor-stimulated arteriogenesis.

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.

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.

Nitroglycerin application and coronary arteriogenesis

BACKGROUND

In the presence of a coronary occlusion, pre-existing small collateral vessels (arterioles) develop into much larger arteries (biological bypasses) that have the potential to allow a certain level of perfusion distal to the blockage. Termed arteriogenesis, this phenomenon proceeds via a complex combination of events, with nitric oxide (NO) playing an essential role. The aim of this study was to investigate the effects of supplemental administration of NO donors, i.e., short-acting nitroglycerin (NTG) or slow-release pelleted isosorbide dinitrate (ISDN), on collateral development in a repetitive coronary artery occlusion model in rats.

METHODS

Coronary collateral growth was induced via a repetitive occlusion protocol (ROP) of the left anterior descending coronary artery (LAD) in rats. The primary endpoints were the histological evaluation of rat heart infarct size and ST-segment elevation (ECG-analysis) upon final permanent occlusion of the LAD (experimentally induced myocardial infarction). The effects of NTG or ISDN were also evaluated by administration during 5 days of ROP. We additionally investigated whether concomitant application of NTG can compensate for the anti-arteriogenic effect of acetylsalicylic acid (ASA).

RESULTS

After 5 days of ROP, the mean infarct size and degree of ST-elevation were only slightly lower than those of the SHAM group; however, after 10 days of the protocol, the ROP group displayed significantly less severe infarct damage, indicating enhanced arteriogenesis. Intermittent NTG application greatly decreased the ST-elevation and infarct size. The ISDN also had a positive effect on arteriogenesis, but not to the same extent as the NTG. Administration of ASA increased the infarct severity; however, concomitant dosing with NTG somewhat attenuated this effect.

CONCLUSION

Intermittent treatment with the short-acting NTG decreased the size of an experimentally induced myocardial infarct by promoting coronary collateral development. These new insights are of great relevance for future clinical strategies for the treatment of occlusive vascular diseases.

Elevated 20-HETE impairs coronary collateral growth in metabolic syndrome via endothelial dysfunction

Coronary collateral growth (CCG) is impaired in metabolic syndrome (MetS). microRNA-145 (miR-145-Adv) delivery to our rat model of MetS (JCR) completely restored and neutrophil depletion significantly improved CCG. We determined whether low endogenous levels of miR-145 in MetS allowed for elevated production of 20-hydroxyeicosatetraenoic acid (20-HETE), which, in turn, resulted in excessive neutrophil accumulation and endothelial dysfunction leading to impaired CCG. Rats underwent 0-9 days of repetitive ischemia (RI). RI-induced cardiac CYP4F (neutrophil-specific 20-HETE synthase) expression and 20-HETE levels were increased (4-fold) in JCR vs. normal rats. miR-145-Adv and 20-HETE antagonists abolished and neutrophil depletion (blocking antibodies) reduced (~60%) RI-induced increases in CYP4F expression and 20-HETE production in JCR rats. Impaired CCG in JCR rats (collateral-dependent blood flow using microspheres) was completely restored by 20-HETE antagonists [collateral-dependent zone (CZ)/normal zone (NZ) flow ratio was 0.76 ± 0.07 in JCR + 20-SOLA, 0.84 ± 0.05 in JCR + 20-HEDGE vs. 0.11 ± 0.02 in JCR vs. 0.84 ± 0.03 in normal rats]. In JCR rats, elevated 20-HETE was associated with excessive expression of endothelial adhesion molecules and neutrophil infiltration, which were reversed by miR-145-Adv. Endothelium-dependent vasodilation of coronary arteries, endothelial nitric oxide synthase (eNOS) Ser1179 phosphorylation, eNOS-dependent NO^·- production and endothelial cell survival were compromised in JCR rats. These parameters of endothelial dysfunction were completely reversed by 20-HETE antagonism or miR-145-Adv delivery, whereas neutrophil depletion resulted in partial reversal (~70%). We conclude that low miR-145 in MetS allows for increased 20-HETE, mainly from neutrophils, which compromises endothelial cell survival and function leading to impaired CCG. 20-HETE antagonists could provide viable therapy for restoration of CCG in MetS.NEW & NOTEWORTHY Elevated 20-hydroxyeicosatetraenoic acid (20-HETE) impairs coronary collateral growth (CCG) in metabolic syndrome by eliciting endothelial dysfunction and apoptosis via excessive neutrophil infiltration. 20-HETE antagonists completely restore coronary collateral growth in metabolic syndrome. microRNA-145 (miR-145) is an upstream regulator of 20-HETE production in metabolic syndrome; low expression of miR-145 in metabolic syndrome promotes elevated production of 20-HETE.

PPARγ activation inhibits cerebral arteriogenesis in the hypoperfused rat brain

AIMS

PPARγ stimulation improves cardiovascular (CV) risk factors, but without improving overall clinical outcomes. PPARγ agonists interfere with endothelial cell (EC), monocyte and smooth muscle cell (SMC) activation, function and proliferation, physiological processes critical for arterial collateral growth (arteriogenesis). We therefore assessed the effect of PPARγ stimulation on cerebral adaptive and therapeutic collateral growth.

METHODS

In a rat model of adaptive cerebral arteriogenesis (3-VO), collateral growth and function were assessed (i) in controls, (ii) after PPARγ stimulation (pioglitazone 2.8 mg kg(-1); 10 mg kg(-1) compared with metformin 62.2 mg kg(-1) or sitagliptin 6.34 mg kg(-1)) for 21 days or (iii) after adding pioglitazone to G-CSF (40 μg kg(-1) every other day) to induce therapeutic arteriogenesis for 1 week. Pioglitazone effects on endothelial and SMC morphology and proliferation, monocyte activation and migration were studied.

RESULTS

PPARγ stimulation decreased cerebrovascular collateral growth and recovery of hemodynamic reserve capacity (CVRC controls: 12 ± 7%; pio low: -2 ± 9%; pio high: 1 ± 7%; metformin: 9 ± 13%; sitagliptin: 11 ± 12%), counteracted G-CSF-induced therapeutic arteriogenesis and interfered with EC activation, SMC proliferation, monocyte activation and migration.

CONCLUSION

Pharmacologic PPARγ stimulation inhibits pro-arteriogenic EC activation, monocyte function, SMC proliferation and thus adaptive as well as G-CSF-induced cerebral arteriogenesis. Further studies should evaluate whether this effect may underlie the CV risk associated with thiazolidinedione use in patients.

Molecular aspects of the cardioprotective effect of exercise in the elderly

Aging is a well-recognized risk factor for several different forms of cardiovascular disease. However, mechanisms by which aging exerts its negative effect on outcome have been only partially clarified. Numerous evidence indicate that aging is associated with alterations of several mechanisms whose integrity confers protective action on the heart and vasculature. The present review aims to focus on the beneficial effects of exercise, which plays a pivotal role in primary and secondary prevention of cardiovascular diseases, in counteracting age-related deterioration of protective mechanisms that are crucially involved in the homeostasis of cardiovascular system. In this regard, animal and human studies indicate that exercise training is able: (1) to improve the inotropic reserve of the aging heart through restoration of cardiac β-adrenergic receptor signaling; (2) to rescue the mechanism of cardiac preconditioning and angiogenesis whose integrity has been shown to confer cardioprotection against ischemia and to improve post-myocardial infarction left ventricular remodeling; (3) to counteract age-related reduction of antioxidant systems that is associated to decreased cellular resistance to reactive oxygen species accumulation. Moreover, this review also describes the molecular effects induced by different exercise training protocols (endurance vs. resistance) in the attempt to better explain what kind of exercise strategy could be more efficacious to improve cardiovascular performance in the elderly population.

Effects of aging on angiogenesis

Aging is a dominant risk factor for most forms of cardiovascular disease. Impaired angiogenesis and endothelial dysfunction likely contribute to the increased prevalence of both cardiovascular diseases and their adverse sequelae in the elderly. Angiogenesis is both an essential adaptive response to physiological stress and an endogenous repair mechanism after ischemic injury. In addition, induction of angiogenesis is a promising therapeutic approach for ischemic diseases. For these reasons, understanding the basis of age-related impairment of angiogenesis and endothelial function has important implications for understanding and managing cardiovascular disease. In this review, we discuss the molecular mechanisms that contribute to impaired angiogenesis in the elderly and potential therapeutic approaches to improving vascular function and angiogenesis in aging patients.

Why is coronary collateral growth impaired in type II diabetes and the metabolic syndrome?

Type II diabetes and the metabolic syndrome are strong predictors of severity of occlusive coronary disease and poorer outcomes of coronary revascularization therapies. Coronary collateral growth can provide an alternative or accessory pathway of revascularization. However, collateral growth is impaired in type II diabetes and the metabolic syndrome. Although many factors necessary for collateral growth are known and many interventions have shown promising results in animal studies, not a single attempt to induce coronary collateral growth in human clinical trials has led to satisfactory results. Accordingly, the first part of this review outlines the known deleterious effects of diabetes and the metabolic syndrome on factors necessary for collateral growth, including pro-angiogenic growth factors, endothelial function, the redox state of the coronary circulation, intracellular signaling, leukocytes and bone marrow-derived progenitors cells. The second section highlights the gaps in our current knowledge of how these factors interact with the radically altered environment of the coronary circulation in diabetes and the metabolic syndrome. The interplay between these pathologies and inadequately explored areas related to the temporal regulation of collateral remodeling and the roles of the extracellular matrix, vascular cell phenotype and pro-inflammatory cytokines are emphasized with implications to development of efficient therapies.

Coronary collateral growth--back to the future

The coronary collateral circulation is critically important as an adaptation of the heart to prevent the damage from ischemic insults. In their native state, collaterals in the heart would be classified as part of the microcirculation, existing as arterial-arterial anastomotic connections in the range of 30 to 100 μM in diameter. However, these vessels also show a propensity to remodel into components of the macrocirculation and can become arteries larger than 1000 μM in diameter. This process of outward remodeling is critically important in the adaptation of the heart to ischemia because the resistance to blood flow is inversely related to the fourth power of the diameter of the vessel. Thus, an expansion of a vessel from 100 to 1000 μM would reduce resistance (in this part of the circuit) to a negligible amount and enable delivery of flow to the region at risk. Our goal in this review is to highlight the voids in understanding this adaptation to ischemia-the growth of the coronary collateral circulation. In doing so we discuss the controversies and unknown aspects of the causal factors that stimulate growth of the collateral circulation, the role of genetics, and the role of endogenous stem and progenitor cells in the context of the normal, physiological situation and under more pathological conditions of ischemic heart disease or with some of the underlying risk factors, e.g., diabetes. The major conclusion of this review is that there are many gaps in our knowledge of coronary collateral growth and this knowledge is critical before the potential of stimulating collateralization in the hearts of patients can be realized. This article is part of a Special Issue entitled "Coronary Blood Flow".

Resolution of mitochondrial oxidative stress rescues coronary collateral growth in Zucker obese fatty rats

OBJECTIVE

We have previously found abrogated ischemia-induced coronary collateral growth in Zucker obese fatty (ZOF) rats compared with Zucker lean (ZLN) rats. Because ZOF rats have structural abnormalities in their mitochondria suggesting dysfunction and also show increased production of O(2), we hypothesized that mitochondrial dysfunction caused by oxidative stress impairs coronary collateral growth in ZOF.

METHODS AND RESULTS

Increased levels of reactive oxygen species were observed in aortic endothelium and smooth muscle cells in ZOF rats compared with ZLN rats. Reactive oxygen species levels were decreased by the mitochondria-targeted antioxidants MitoQuinone (MQ) and MitoTempol (MT) as assessed by MitoSox Red and dihydroethidine staining. Lipid peroxides (a marker of oxidized lipids) were increased in ZOF by ≈47% compared with ZLN rats. The elevation in oxidative stress was accompanied by increased antioxidant enzymes, except glutathione peroxidase-1, and by increased uncoupling protein-2 in ZOF versus ZLN rats. In addition, elevated respiration rates were also observed in the obese compared with lean rats. Administration of MQ significantly normalized the metabolic profiles and reduced lipid peroxides in ZOF rats to the same level observed in lean rats. The protective effect of MQ also suppressed the induction of uncoupling protein-2 in the obese rats. Resolution of mitochondrial oxidative stress by MQ or MT restored coronary collateral growth to the same magnitude observed in ZLN rats in response to repetitive ischemia.

CONCLUSIONS

We conclude that mitochondrial oxidative stress and dysfunction play a key role in disrupting coronary collateral growth in obesity and the metabolic syndrome, and elimination of the mitochondrial oxidative stress with MQ or MT rescues collateral growth.

G-CSF therapy reduces myocardial repolarization reserve in the presence of increased arteriogenesis, angiogenesis and connexin 43 expression in an experimental model of pacing-induced heart failure

G-CSF (granulocyte colony-stimulating factor) treatment has been shown to cause beneficial effects including a reduction of inducible arrhythmias in rodent models of ischemic cardiomyopathy. The aim of the present study was to test whether these effects do also apply to pacing-induced non-ischemic heart failure. In 24 female rabbits, heart failure was induced by rapid ventricular pacing. 24 rabbits were sham operated. The paced rabbits developed a significant decrease of ejection fraction. 11 heart failure rabbits (CHF) and 11 sham-operated (S) rabbits served as controls, whereas 13 sham (S-G-CSF) and 13 heart failure rabbits (CHF-G-CSF) were treated with 10 μg/kg G-CSF s.c. over 17 ± 4 days. G-CSF treatment caused a ~25% increased arterial and capillary density and a ~60% increased connexin 43 expression in failing hearts. In isolated, Langendorff-perfused rabbit hearts eight monophasic action potential recordings showed prolongation of repolarization in CHF as compared with controls in the presence of the QT prolonging agent erythromycin (+33 ± 12 ms; p < 0.01). Moreover, a significant increase in dispersion of repolarization contributed to a significantly higher rate of ventricular tachyarrhythmias in CHF. G-CSF-pre-treated hearts showed a further increase in prolongation of repolarization as compared with S and CHF. The further increase in dispersion of repolarization [S-G-CSF: +23 ± 9 ms (spatial), +13 ± 7 ms (temporal); CHF-G-CSF: +38 ± 14 ms (spatial), +10 ± 4 ms (temporal); p < 0.05 as compared with S and CHF], increased the incidence of ventricular tachyarrhythmias. In summary, chronic G-CSF treatment has moderate beneficial effects on parameters potentially related to hemodynamic function in the non-ischemic rabbit CHF model. However, a significant reduction of repolarization reserve might seriously challenge its suitability as a therapeutic agent for chronic CHF therapy.