Dynamic synchrotron imaging of diabetic rat coronary microcirculation in vivo

Coronary Artery Spasm-Related Heart Failure Syndrome: Literature Review

Although heart failure (HF) is a clinical syndrome that becomes worse over time, certain cases can be reversed with appropriate treatments. While coronary artery spasm (CAS) is still underappreciated and may be misdiagnosed, ischemia due to coronary artery disease and CAS is becoming the single most frequent cause of HF worldwide. CAS could lead to syncope, HF, arrhythmias, and myocardial ischemic syndromes such as asymptomatic ischemia, rest and/or effort angina, myocardial infarction, and sudden death. Albeit the clinical significance of asymptomatic CAS has been undervalued, affected individuals compared with those with classic Heberden's angina pectoris are at higher risk of syncope, life-threatening arrhythmias, and sudden death. As a result, a prompt diagnosis implements appropriate treatment strategies, which have significant life-changing consequences to prevent CAS-related complications, such as HF. Although an accurate diagnosis depends mainly on coronary angiography and provocative testing, clinical characteristics may help decision-making. Because the majority of CAS-related HF (CASHF) patients present with less severe phenotypes than overt HF, it underscores the importance of understanding risk factors correlated with CAS to prevent the future burden of HF. This narrative literature review summarises and discusses separately the epidemiology, clinical features, pathophysiology, and management of patients with CASHF.

Using Synchrotron Radiation Imaging Techniques to Elucidate the Actions of Hexarelin in the Heart of Small Animal Models

The majority of the conventional techniques that are utilized for investigating the pathogenesis of cardiovascular disease in preclinical animal models do not permit microlevel assessment of in situ cardiomyocyte and microvascular functions. Therefore, it has been difficult to establish whether cardiac dysfunction in complex multiorgan disease states, such as heart failure with preserved ejection fraction and pulmonary hypertension, have their origins in microvascular dysfunction or rather in the cardiomyocyte. Herein, we describe our approach of utilizing synchrotron radiation microangiography to, first, ascertain whether the growth hormone secretagogue (GHS) hexarelin is a vasodilator in the coronary circulation of normal and anesthetized Sprague-Dawley rats, and next investigate if hexarelin is able to prevent the pathogenesis of right ventricle (RV) dysfunction in pulmonary hypertension in the sugen chronic hypoxia model rat. We show that acute hexarelin administration evokes coronary microvascular dilation through GHS-receptor 1a and nitric oxide, and through endothelium-derived hyperpolarization. Previous work indicated that chronic exogenous administration of ghrelin largely prevented the pathogenesis of pulmonary hypertension in chronic hypoxia and in monocrotaline models. Unexpectedly, chronic hexarelin administration prior to sugen chronic hypoxia did not prevent RV hypertrophy or RV cardiomyocyte relaxation impairment. Small-angle X-ray scattering revealed that super relaxed myosin filaments contributed to diastolic dysfunction, and that length-dependent activation might contribute to sustained contractility of the RV. Thus, synchrotron-based imaging approaches can reveal novel insights into cardiac and coronary functions in vivo.

Noninvasive assessment of coronary microvascular dysfunction using SPECT myocardial perfusion imaging and myocardial perfusion entropy quantification in a rodent model of type 2 diabetes

PURPOSE

Coronary microvascular dysfunction (CMVD) plays a major role in the occurrence of cardiovascular events (CVE). We recently suggested the clinical potential of myocardial perfusion entropy (MPE) quantification from SPECT myocardial perfusion images (MPI) for the prognosis of CVE occurrence. We hypothesized that the quantification of MPE from SPECT MPI would allow the assessment of CMVD-related MPE variations in a preclinical model of type 2 diabetes (T2D) including treatment with the anti-diabetic incretin liraglutide (LIR).

METHODS

Optimal conditions for the preclinical quantification of MPE using ²⁰¹Tl SPECT MPI were determined in rats with a T2D-like condition induced by a high-fat diet and streptozotocin injection (feasibility study, n = 43). Using such conditions, echocardiography and post-mortem LV capillary density evaluation were then used in order to assess the effect of LIR and the ability of MPE to assess CMVD (therapeutic study, n = 39).

RESULTS

The feasibility study identified dobutamine stress and acute NO synthase and cyclooxygenase inhibition as optimal conditions for the quantification of MPE, with significant increases in MPE being observed in T2D animals (P < 0.01 vs controls). In the therapeutic study, T2D rats were hyperglycemic (5.5 ± 0.5 vs 1.1 ± 0.3 g/L for controls, P < 0.001) and had a significantly lower left ventricular ejection fraction (LVEF) (65 ± 4% vs 74 ± 9%, P < 0.01) and LV capillary density (2400 ± 300 vs 2800 ± 600 mm^-3, P < 0.05). LIR partially restored glycemia (3.9 ± 0.6 g/L, P < 0.05 vs controls and T2D), totally prevented LVEF impairment (72 ± 7%, P = NS vs CTL), with no significant effect on capillary density. MPE was significantly increased in T2D rats (7.6 ± 0.5 vs 7.1 ± 0.5, P < 0.05), with no significant improvement in T2D-LIR rats (7.4 ± 0.4, P = NS vs controls and T2D).

CONCLUSION

MPE quantification allowed the preclinical noninvasive assessment of CMVD. Both MPE and capillary density quantification suggested that LIR did not improve T2D-induced CMVD. The relevance of MPE for CMVD assessment warrants further clinical investigation.

Three-dimensional-arterial spin labeling perfusion correlation with diabetes-associated cognitive dysfunction and vascular endothelial growth factor in type 2 diabetes mellitus rat

BACKGROUND

Type 2 diabetes mellitus (T2DM) has been strongly associated with an increased risk of developing cognitive dysfunction and dementia. The mechanisms of diabetes-associated cognitive dysfunction (DACD) have not been fully elucidated to date. Some studies proved lower cerebral blood flow (CBF) in the hippocampus was associated with poor executive function and memory in T2DM. Increasing evidence showed that diabetes leads to abnormal vascular endothelial growth factor (VEGF) expression and CBF changes in humans and animal models. In this study, we hypothesized that DACD was correlated with CBF alteration as measured by three-dimensional (3D) arterial spin labeling (3D-ASL) and VEGF expression in the hippocampus.

AIM

To assess the correlation between CBF (measured by 3D-ASL and VEGF expression) and DACD in a rat model of T2DM.

METHODS

Forty Sprague-Dawley male rats were divided into control and T2DM groups. The T2DM group was established by feeding rats a high-fat diet and glucose to induce impaired glucose tolerance and then injecting them with streptozotocin to induce T2DM. Cognitive function was assessed using the Morris water maze experiment. The CBF changes were measured by 3D-ASL magnetic resonance imaging. VEGF expression was determined using immunofluorescence.

RESULTS

The escape latency time significantly reduced 15 wk after streptozotocin injection in the T2DM group. The total distance traveled was longer in the T2DM group; also, the platform was crossed fewer times. The percentage of distance in the target zone significantly decreased. CBF decreased in the bilateral hippocampus in the T2DM group. No difference was found between the right CBF value and the left CBF value in the T2DM group. The VEGF expression level in the hippocampus was lower in the T2DM group and correlated with the CBF value. The escape latency negatively correlated with the CBF value. The number of rats crossing the platform positively correlated with the CBF value.

CONCLUSION

Low CBF in the hippocampus and decreased VEGF expression might be crucial in DACD. CBF measured by 3D-ASL might serve as a noninvasive imaging biomarker for cognitive impairment associated with T2DM.

Evaluation of right coronary vascular dysfunction in severe pulmonary hypertensive rats using synchrotron radiation microangiography

Pulmonary hypertension (PH) causes cardiac hypertrophy in the right ventricle (RV) and eventually leads to RV failure due to persistently elevated ventricular afterload. We hypothesized that the mechanical stress on the RV associated with increased afterload impairs vasodilator function of the right coronary artery (RCA) in PH. Coronary vascular response was assessed using microangiography with synchrotron radiation (SR) in two well-established PH rat models, monocrotaline injection or the combined exposure to chronic hypoxia and vascular endothelial growth factor receptor blockade with Su5416 (SuHx model). In the SuHx model, the effect of the treatment with the nonselective endothelin-1 receptor antagonist (ERA), macitentan, was also examined. Myocardial viability was determined in SuHx model rats, using 18F-FDG Positron emission tomography (PET) and magnetic resonance imaging (MRI). Endothelium-dependent and endothelium-independent vasodilator responses were significantly attenuated in the medium and small arteries of severe PH rats. ERA treatment significantly improved RCA vascular function compared with the untreated group. ERA treatment improved both the decrease in ejection fraction and the increased glucose uptake, and reduced RV remodeling. In addition, the upregulation of inflammatory genes in the RV was almost suppressed by ERA treatment. We found impairment of vasodilator responses in the RCA of severe PH rat models. Endothelin-1 activation in the RCA plays a major role in impaired vascular function in PH rats and is partially restored by ERA treatment. Treatment of PH with ERA may improve RV function in part by indirectly attenuating right heart afterload and in part by associated improvements in right coronary endothelial function.NEW & NOTEWORTHY We demonstrated for the first time the impairment of vascular responses in the right coronary artery (RCA) of the dysfunctional right heart in pulmonary hypertensive rats in vivo. Treatment with an endothelin-1 receptor antagonist ameliorated vascular dysfunction in the RCA, enabled tissue remodeling of the right heart, and improved cardiac function. Our results suggest that impaired RCA function might also contribute to the early progression to heart failure in patients with severe pulmonary arterial hypertension (PAH). The endothelium of the coronary vasculature might be considered as a potential target in treatments to prevent heart failure in severe patients with PAH.

β-blockade prevents coronary macro- and microvascular dysfunction induced by a high salt diet and insulin resistance in the Goto-Kakizaki rat

A high salt intake exacerbates insulin resistance, evoking hypertension due to systemic perivascular inflammation, oxidative-nitrosative stress and endothelial dysfunction. Angiotensin-converting enzyme inhibitor (ACEi) and angiotensin receptor blockers (ARBs) have been shown to abolish inflammation and redox stress but only partially restore endothelial function in mesenteric vessels. We investigated whether sympatho-adrenal overactivation evokes coronary vascular dysfunction when a high salt intake is combined with insulin resistance in male Goto-Kakizaki (GK) and Wistar rats treated with two different classes of β-blocker or vehicle, utilising synchrotron-based microangiography in vivo. Further, we examined if chronic carvedilol (CAR) treatment preserves nitric oxide (NO)-mediated coronary dilation more than metoprolol (MET). A high salt diet (6% NaCl w/w) exacerbated coronary microvessel endothelial dysfunction and NO-resistance in vehicle-treated GK rats while Wistar rats showed modest impairment. Microvascular dysfunction was associated with elevated expression of myocardial endothelin, inducible NO synthase (NOS) protein and 3-nitrotyrosine (3-NT). Both CAR and MET reduced basal coronary perfusion but restored microvessel endothelium-dependent and -independent dilation indicating a role for sympatho-adrenal overactivation in vehicle-treated rats. While MET treatment reduced myocardial nitrates, only MET treatment completely restored microvessel dilation to dobutamine (DOB) stimulation in the absence of NO and prostanoids (combined inhibition), indicating that MET restored the coronary flow reserve attributable to endothelium-derived hyperpolarisation (EDH). In conclusion, sympatho-adrenal overactivation caused by high salt intake and insulin resistance evoked coronary microvessel endothelial dysfunction and diminished NO sensitivity, which were restored by MET and CAR treatment in spite of ongoing inflammation and oxidative-nitrosative stress presumably caused by uninhibited renin-angiotensin-aldosterone system (RAAS) overactivation.

Experimental animal models of coronary microvascular dysfunction

Coronary microvascular dysfunction (CMD) is commonly present in patients with metabolic derangements and is increasingly recognized as an important contributor to myocardial ischaemia, both in the presence and absence of epicardial coronary atherosclerosis. The latter condition is termed 'ischaemia and no obstructive coronary artery disease' (INOCA). Notwithstanding the high prevalence of INOCA, effective treatment remains elusive. Although to date there is no animal model for INOCA, animal models of CMD, one of the hallmarks of INOCA, offer excellent test models for enhancing our understanding of the pathophysiology of CMD and for investigating novel therapies. This article presents an overview of currently available experimental models of CMD-with an emphasis on metabolic derangements as risk factors-in dogs, swine, rabbits, rats, and mice. In all available animal models, metabolic derangements are most often induced by a high-fat diet (HFD) and/or diabetes mellitus via injection of alloxan or streptozotocin, but there is also a wide variety of spontaneous as well as transgenic animal models which develop metabolic derangements. Depending on the number, severity, and duration of exposure to risk factors-all these animal models show perturbations in coronary microvascular (endothelial) function and structure, similar to what has been observed in patients with INOCA and comorbid conditions. The use of these animal models will be instrumental in identifying novel therapeutic targets and for the subsequent development and testing of novel therapeutic interventions to combat ischaemic heart disease, the number one cause of death worldwide.

Endothelium-Dependent Hyperpolarization (EDH) in Diabetes: Mechanistic Insights and Therapeutic Implications

Diabetes mellitus is one of the major risk factors for cardiovascular disease and is an important health issue worldwide. Long-term diabetes causes endothelial dysfunction, which in turn leads to diabetic vascular complications. Endothelium-derived nitric oxide is a major vasodilator in large-size vessels, and the hyperpolarization of vascular smooth muscle cells mediated by the endothelium plays a central role in agonist-mediated and flow-mediated vasodilation in resistance-size vessels. Although the mechanisms underlying diabetic vascular complications are multifactorial and complex, impairment of endothelium-dependent hyperpolarization (EDH) of vascular smooth muscle cells would contribute at least partly to the initiation and progression of microvascular complications of diabetes. In this review, we present the current knowledge about the pathophysiology and underlying mechanisms of impaired EDH in diabetes in animals and humans. We also discuss potential therapeutic approaches aimed at the prevention and restoration of EDH in diabetes.

Widespread Coronary Dysfunction in the Absence of HDL Receptor SR-B1 in an Ischemic Cardiomyopathy Mouse Model

Reduced clearance of lipoproteins by HDL scavenger receptor class B1 (SR-B1) plays an important role in occlusive coronary artery disease. However, it is not clear how much microvascular dysfunction contributes to ischemic cardiomyopathy. Our aim was to determine the distribution of vascular dysfunction in vivo in the coronary circulation of male mice after brief exposure to Paigen high fat diet, and whether this vasomotor dysfunction involved nitric oxide (NO) and or endothelium derived hyperpolarization factors (EDHF). We utilised mice with hypomorphic ApoE lipoprotein that lacked SR-B1 (SR-B1^−/−/ApoER61^h/h, n = 8) or were heterozygous for SR-B1 (SR-B1^+/−/ApoER61^h/h, n = 8) to investigate coronary dilator function with synchrotron microangiography. Partially occlusive stenoses were observed in vivo in SR-B1 deficient mice only. Increases in artery-arteriole calibre to acetylcholine and sodium nitroprusside stimulation were absent in SR-B1 deficient mice. Residual dilation to acetylcholine following L-NAME (50 mg/kg) and sodium meclofenamate (3 mg/kg) blockade was present in both mouse groups, except at occlusions, indicating that EDHF was not impaired. We show that SR-B1 deficiency caused impairment of NO-mediated dilation of conductance and microvessels. Our findings also suggest EDHF and prostanoids are important for global perfusion, but ultimately the loss of NO-mediated vasodilation contributes to atherothrombotic progression in ischemic cardiomyopathy.

Tissue-engineered smooth muscle cell and endothelial progenitor cell bi-level cell sheets prevent progression of cardiac dysfunction, microvascular dysfunction, and interstitial fibrosis in a rodent model of type 1 diabetes-induced cardiomyopathy

Background

Diabetes mellitus is a risk factor for coronary artery disease and diabetic cardiomyopathy, and adversely impacts outcomes following coronary artery bypass grafting. Current treatments focus on macro-revascularization and neglect the microvascular disease typical of diabetes mellitus-induced cardiomyopathy (DMCM). We hypothesized that engineered smooth muscle cell (SMC)-endothelial progenitor cell (EPC) bi-level cell sheets could improve ventricular dysfunction in DMCM.

Methods

Primary mesenchymal stem cells (MSCs) and EPCs were isolated from the bone marrow of Wistar rats, and MSCs were differentiated into SMCs by culturing on a fibronectin-coated dish. SMCs topped with EPCs were detached from a temperature-responsive culture dish to create an SMC-EPC bi-level cell sheet. A DMCM model was induced by intraperitoneal streptozotocin injection. Four weeks after induction, rats were randomized into 3 groups: control (no DMCM induction), untreated DMCM, and treated DMCM (cell sheet transplant covering the anterior surface of the left ventricle).

Results

SMC-EPC cell sheet therapy preserved cardiac function and halted adverse ventricular remodeling, as demonstrated by echocardiography and cardiac magnetic resonance imaging at 8 weeks after DMCM induction. Myocardial contrast echocardiography demonstrated that myocardial perfusion and microvascular function were preserved in the treatment group compared with untreated animals. Histological analysis demonstrated decreased interstitial fibrosis and increased microvascular density in the SMC-EPC cell sheet-treated group.

Conclusions

Treatment of DMCM with tissue-engineered SMC-EPC bi-level cell sheets prevented cardiac dysfunction and microvascular disease associated with DMCM. This multi-lineage cellular therapy is a novel, translatable approach to improve microvascular disease and prevent heart failure in diabetic patients.

Image-based modelling of skeletal muscle oxygenation

The supply of oxygen in sufficient quantity is vital for the correct functioning of all organs in the human body, in particular for skeletal muscle during exercise. Disease is often associated with both an inhibition of the microvascular supply capability and is thought to relate to changes in the structure of blood vessel networks. Different methods exist to investigate the influence of the microvascular structure on tissue oxygenation, varying over a range of application areas, i.e. biological in vivo and in vitro experiments, imaging and mathematical modelling. Ideally, all of these methods should be combined within the same framework in order to fully understand the processes involved. This review discusses the mathematical models of skeletal muscle oxygenation currently available that are based upon images taken of the muscle microvasculature in vivo and ex vivo Imaging systems suitable for capturing the blood vessel networks are discussed and respective contrasting methods presented. The review further informs the association between anatomical characteristics in health and disease. With this review we give the reader a tool to understand and establish the workflow of developing an image-based model of skeletal muscle oxygenation. Finally, we give an outlook for improvements needed for measurements and imaging techniques to adequately investigate the microvascular capability for oxygen exchange.

Enhanced adhesion of blood platelets to intact endothelium of mesenteric vascular bed in mice with streptozotocin-induced diabetes is mediated by an up-regulated endothelial surface deposition of VWF - In vivo study

Numerous in vitro experiments have confirmed that a dysfunctional endothelium is characterized by, inter alia, a higher affinity for binding of platelets and leukocytes. However, there is still no direct evidence for greater interaction between platelets and intact endothelium in in vivo animal models of diabetes. Therefore, the present study examines the pro-adhesive properties of endothelium change in vivo as an effect of streptozotocin (STZ)-induced diabetes and the role of two key platelet receptors: GPIb-IX-V and GPIIb/IIIa. Mice of C57BL strain with streptozotocin-induced diabetes were used in the study. Flow cytometry was used to assess basal activation and reactivity of platelets. Adhesion of platelets to the vascular wall was visualized with the use of intravital microscopy in mesentery. The contribution of GPIIb/IIIa and GPIb-IX-V was evaluated by the injection of Fab fragments of respective antibodies. The integrity of the endothelium and vWf expression were evaluated histochemically. Basal activation and reactivity of platelets in streptozotocin-diabetic mice were elevated. Blood platelets adhered more often to the vascular wall of diabetic mice than nondiabetic animals: 11.9 (6.4; 32.8) plt/min/mm² (median [IQR]) vs 2.7 (1.3; 6.4) plt/min/mm². The injection of anti-GPIbα antibodies decreased the number of adhering platelets from 89.5 (34.0; 113.1) plt/min/mm² (median [IQR]) in mice treated with isotype antibodies to 3.1 (1.7; 5.6) plt/min/mm² in mice treated with blocking antibodies. The effect of GPIIb/IIIa blockage was not significant. Immunohistochemistry revealed a higher expression of vWF in the endothelium of STZ mice, but no substantial changes in endothelial morphology were detected. To conclude, the study shows that the platelets interact more frequently with the mesenteric vascular bed in mice with 1-month STZ-induced diabetes than in healthy mice. These interactions are mediated via platelet GPIb-IX-V and are driven by increased expression of vWF in endothelial cells.

RhoA/rock signaling mediates peroxynitrite-induced functional impairment of Rat coronary vessels

Background

Diabetes-induced vascular dysfunction may arise from reduced nitric oxide (NO) availability, following interaction with superoxide to form peroxynitrite. Peroxynitrite can induce formation of 3-nitrotyrosine-modified proteins. RhoA/ROCK signaling is also involved in diabetes-induced vascular dysfunction. The study aimed to investigate possible links between Rho/ROCK signaling, hyperglycemia, and peroxynitrite in small coronary arteries.

Methods

Rat small coronary arteries were exposed to normal (NG; 5.5 mM) or high (HG; 23 mM) D-glucose. Vascular ring constriction to 3 mM 4-aminopyridine and dilation to 1 μM forskolin were measured. Protein expression (immunohistochemistry and western blot), mRNA expression (real-time PCR), and protein activity (luminescence-based G-LISA and kinase activity spectroscopy assays) of RhoA, ROCK1, and ROCK2 were determined.

Results

Vascular ring constriction and dilation were smaller in the HG group than in the NG group (P < 0.05); inhibition of RhoA or ROCK partially reversed the effects of HG. Peroxynitrite impaired vascular ring constriction/dilation; this was partially reversed by inhibition of RhoA or ROCK. Protein and mRNA expressions of RhoA, ROCK1, and ROCK2 were higher under HG than NG (P < 0.05). This HG-induced upregulation was attenuated by inhibition of RhoA or ROCK (P < 0.05). HG increased RhoA, ROCK1, and ROCK2 activity (P < 0.05). Peroxynitrite also enhanced RhoA, ROCK1, and ROCK2 activity; these actions were partially inhibited by 100 μM urate (peroxynitrite scavenger). Exogenous peroxynitrite had no effect on the expression of the voltage-dependent K⁺ channels 1.2 and 1.5.

Conclusions

Peroxynitrite-induced coronary vascular dysfunction may be mediated, at least in part, through increased expressions and activities of RhoA, ROCK1, and ROCK2.

Evidence for elevated (LIMK2 and CFL1) and suppressed (ICAM1, EZR, MAP2K2, and NOS3) gene expressions in metabolic syndrome

The metabolic syndrome (MetS) is a common multicomponent condition including abdominal obesity, dyslipidemia, hypertension, and hyperglycaemia. The aim of this study was to investigate the associations of the expression of a panel of signalling genes with the MetS in a Turkish population. A total of 54 MetS patients and 42 healthy controls with similar age and sex were included to this study. mRNA from blood samples was extracted, and real-time polymerase chain reaction was performed for gene expressions using a BioMark 96.96 dynamic array system. We observed marked increases in LIM kinase 2 (LIMK2) and cofilin 1 (CFL1) gene expressions in MetS patients. However, there were significant decreases in intercellular adhesion molecules 1 (ICAM1), ezrin (EZR), mitogen-activated protein kinase kinase 2 (MAP2K2), and nitric oxide synthase 3 (NOS3) gene expressions in MetS patients. Additionally, no marked changes were noted in other 15 genes studied. This is the first study to provide evidence that activation of LIMK2/CFL1 pathway may play an important role in MetS.

Chronic intermittent hypoxia accelerates coronary microcirculatory dysfunction in insulin-resistant Goto-Kakizaki rats

Chronic intermittent hypoxia (IH) induces oxidative stress and inflammation, which impair vascular endothelial function. Long-term insulin resistance also leads to endothelial dysfunction. We determined, in vivo, whether the effects of chronic IH and insulin resistance on endothelial function augment each other. Male 12-wk-old Goto-Kakizaki (GK) and Wistar control rats were subjected to normoxia or chronic IH (90-s N2, 5% O2 at nadir, 90-s air, 20 cycles/h, 8 h/day) for 4 wk. Coronary endothelial function was assessed using microangiography with synchrotron radiation. Imaging was performed at baseline, during infusion of acetylcholine (ACh, 5 μg·kg−1·min−1) and then sodium nitroprusside (SNP, 5 μg·kg−1·min−1), after blockade of both nitric oxide (NO) synthase (NOS) with Nω-nitro-l-arginine methyl ester (l-NAME, 50 mg/kg) and cyclooxygenase (COX, meclofenamate, 3 mg/kg), and during subsequent ACh. In GK rats, coronary vasodilatation in response to ACh and SNP was blunted compared with Wistar rats, and responses to ACh were abolished after blockade. In Wistar rats, IH blunted the ability of ACh or SNP to increase the number of visible vessels. In GK rats exposed to IH, neither ACh nor SNP were able to increase visible vessel number or caliber, and blockade resulted in marked vasoconstriction. Our findings indicate that IH augments the deleterious effects of insulin resistance on coronary endothelial function. They appear to increase the dependence of the coronary microcirculation on NO and/or vasodilator prostanoids, and greatly blunt the residual vasodilation in response to ACh after blockade of NOS/COX, presumably mediated by endothelium-derived hyperpolarizing factors.

Vessel Dilation Attenuates Endothelial Dysfunction Following Middle Cerebral Artery Occlusion in Hyperglycemic Rats

OBJECTIVES

Dynamically observe cerebral vascular changes in hyperglycemic rats in vivo and explore the effect of diabetes on endothelial function after ischemic stroke.

BACKGROUND

Diabetes affects both large and small vessels in the brain, but the dynamic process and mechanism are unclear.

METHODS

We investigated the structural and functional changes of brain vasculature in living hyperglycemic rats and their impact on stroke outcomes via a novel technique: synchrotron radiation angiography. We also examined the effect of prolonged fasudil treatment on arterial reactivity and hemorrhagic transformation. Adult Sprague Dawley rats were treated by streptozotocin to induce type 1 diabetes. These hyperglycemic rats received fasudil pretreatment and then underwent transient middle cerebral artery occlusion.

RESULTS

We found that diabetes caused arteries narrowing in the circus Willis as early as 2 weeks after streptozotocin injection (P < 0.05). These vessels were further constricted after middle cerebral artery occlusion. L-NAME could induce regional constrictions and impaired relaxation in hyperglycemic animals. Furthermore, hemorrhagic transformation was also increased in the hyperglycemic rats compared to the control (P < 0.05). In fasudil-treated rats, the internal carotid artery narrowing was ameliorated and L-NAME-induced regional constriction was abolished. Importantly, stroke prognosis was improved in fasudil-treated rats compared to the control (P < 0.05).

CONCLUSIONS

Our dynamic angiographic data demonstrated that diabetes could impair the cerebral arterial reactivity. Prolonged fasudil treatment could attenuate arterial dysfunction and improve the prognosis of ischemic stroke by affecting both the large and small vasculature.

Ultra High-Resolution In vivo Computed Tomography Imaging of Mouse Cerebrovasculature Using a Long Circulating Blood Pool Contrast Agent

Abnormalities in the cerebrovascular system play a central role in many neurologic diseases. The on-going expansion of rodent models of human cerebrovascular diseases and the need to use these models to understand disease progression and treatment has amplified the need for reproducible non-invasive imaging methods for high-resolution visualization of the complete cerebral vasculature. In this study, we present methods for in vivo high-resolution (19 μm isotropic) computed tomography imaging of complete mouse brain vasculature. This technique enabled 3D visualization of large cerebrovascular networks, including the Circle of Willis. Blood vessels as small as 40 μm were clearly delineated. ACTA2 mutations in humans cause cerebrovascular defects, including abnormally straightened arteries and a moyamoya-like arteriopathy characterized by bilateral narrowing of the internal carotid artery and stenosis of many large arteries. In vivo imaging studies performed in a mouse model of Acta2 mutations demonstrated the utility of this method for studying vascular morphometric changes that are practically impossible to identify using current histological methods. Specifically, the technique demonstrated changes in the width of the Circle of Willis, straightening of cerebral arteries and arterial stenoses. We believe the use of imaging methods described here will contribute substantially to the study of rodent cerebrovasculature.

Treadmill running improves hindlimb arteriolar endothelial function in type 1 diabetic mice as visualized by X-ray microangiography

BACKGROUND

Vascular function is impaired in patients with diabetes, however diabetic vascular dysfunction is ameliorated by exercise training. We aimed to clarify which hindlimb arterial segments are affected by treadmill running in the hindlimbs of streptozocin-induced type 1 diabetic mice in vivo.

METHODS

Mice were divided into 3 groups; healthy control, diabetic control, and diabetic-running groups. The exercise regimen was performed by treadmill level running mice for 60 min/day, for 4 weeks. Thereafter, we examined the vascular response to systemic acetylcholine administration in the left hindlimb of anesthetized-ventilated mice using either 1) X-ray microangiography to visualize the arteries or 2) ultrasonic flowmetry to record the femoral arterial blood flow.

RESULTS

X-ray imaging clearly visualized the hindlimb arterial network (~70-250 μm diameter). The vasodilator response to acetylcholine was significantly attenuated locally in the arterioles <100 μm diameter in the diabetic group of mice compared to the control group of mice. Post-acetylcholine administration, all groups showed an increase in hindlimb vascular conductance, but the diabetic mice showed the smallest increase. Overall, compared to the diabetic mice, the treadmill-running mice exhibited a significant enhancement of the vasodilator response within the arterioles with diabetes-induced vasodilator dysfunction.

CONCLUSIONS

Diabetes impaired acetylcholine-induced vasodilator function locally in the arteries <100 μm diameter and decreased hindlimb vascular conductance responded to acetylcholine, while regular treadmill running significantly ameliorated the impaired vasodilator function, and enhanced the decreased conductance in the diabetic mice.

Development of functional in vivo imaging of cerebral lenticulostriate artery using novel synchrotron radiation angiography

The lenticulostriate artery plays a vital role in the onset and development of cerebral ischemia. However, current imaging techniques cannot assess the in vivo functioning of small arteries such as the lenticulostriate artery in the brain of rats. Here, we report a novel method to achieve a high resolution multi-functional imaging of the cerebrovascular system using synchrotron radiation angiography, which is based on spatio-temporal analysis of contrast density in the arterial cross section. This method provides a unique tool for studying the sub-cortical vascular elasticity after cerebral ischemia in rats. Using this technique, we demonstrated that the vascular elasticity of the lenticulostriate artery decreased from day 1 to day 7 after transient middle cerebral artery occlusion in rats and recovered from day 7 to day 28 compared to the controls (p < 0.001), which paralleled with brain edema formation and inversely correlated with blood flow velocity (p < 0.05). Our results demonstrated that the change of vascular elasticity was related to the levels of brain edema and the velocity of focal blood flow, suggesting that reducing brain edema is important for the improvement of the function of the lenticulostriate artery in the ischemic brain.

Cell-sheet therapy with omentopexy promotes arteriogenesis and improves coronary circulation physiology in failing heart

Cell-sheet transplantation induces angiogenesis for chronic myocardial infarction (MI), though insufficient capillary maturation and paucity of arteriogenesis may limit its therapeutic effects. Omentum has been used clinically to promote revascularization and healing of ischemic tissues. We hypothesized that cell-sheet transplantation covered with an omentum-flap would effectively establish mature blood vessels and improve coronary microcirculation physiology, enhancing the therapeutic effects of cell-sheet therapy. Rats were divided into four groups after coronary ligation; skeletal myoblast cell-sheet plus omentum-flap (combined), cell-sheet only, omentum-flap only, and sham operation. At 4 weeks after the treatment, the combined group showed attenuated cardiac hypertrophy and fibrosis, and a greater amount of functionally (CD31(+)/lectin(+)) and structurally (CD31(+)/α-SMA(+)) mature blood vessels, along with myocardial upregulation of relevant genes. Synchrotron-based microangiography revealed that the combined procedure increased vascularization in resistance arterial vessels with better dilatory responses to endothelium-dependent agents. Serial (13)N-ammonia PET showed better global coronary flow reserve in the combined group, mainly attributed to improvement in the basal left ventricle. Consequently, the combined group had sustained improvements in cardiac function parameters and better functional capacity. Cell-sheet transplantation with an omentum-flap better promoted arteriogenesis and improved coronary microcirculation physiology in ischemic myocardium, leading to potent functional recovery in the failing heart.

Acute Rho-kinase inhibition improves coronary dysfunction in vivo, in the early diabetic microcirculation

OBJECTIVES

Activation of RhoA/Rho-kinase (ROCK) is increasingly implicated in acute vasospasm and chronic vasoconstriction in major organ systems. Therefore we aimed to ascertain whether an increase in ROCK activity plays a role in the deterioration of coronary vascular function in early stage diabetes.

METHODS

Synchrotron radiation microangiography was used to determine in vivo coronary responses in diabetic (3 weeks post streptozotocin 65 mg/kg ip) and vehicle treated male Sprague-Dawley rats (n = 8 and 6). Changes in vessel number and calibre during vasodilator stimulation before and after blockade of nitric oxide synthase and cyclooxygenase were compared between rats. Acute responses to ROCK inhibitor, fasudil (10 mg/kg iv) was evaluated. Further, perivascular and myocardial fibrosis, arterial intimal thickening were assessed by histology, and capillary density, nitrotyrosine and ROCK1/2 expressions were evaluated by immunohistochemical staining.

RESULTS

Diabetic rats had significantly elevated plasma glucose (P < 0.001 vs control), but did not differ in fibrotic scores, media to lumen ratio, capillary density or baseline visible vessel number or calibre. Responses to acetylcholine and sodium nitroprusside stimulation were similar between groups. However, in comparison to control rats the diabetic rats showed more segmental constrictions during blockade, which were not completely alleviated by acetylcholine, but were alleviated by fasudil. Further, second order vessel branches in diabetic rats were significantly more dilated relative to baseline (37% vs 12% increase, P < 0.05) after fasudil treatment compared to control rats, while visible vessel number increased in both groups. ROCK2 expression was borderline greater in diabetic rat hearts (P < 0.053).

CONCLUSIONS

We found that ahead of the reported decline in coronary endothelial vasodilator function in diabetic rats there was moderate elevation in ROCK expression, more widespread segmental constriction when nitric oxide and prostacyclin production were inhibited and notably, increased calibre in second and third order small arteries-arterioles following ROCK inhibition. Based on nitrotyrosine staining oxidative stress was not significantly elevated in early diabetic rats. We conclude that tonic ROCK mediated vasoconstriction contributes to coronary vasomotor tone in early diabetes.

X-ray intravital microscopy for functional imaging in rat hearts using synchrotron radiation coronary microangiography

An X-ray intravital microscopy technique was developed to enable in vivo visualization of the coronary, cerebral, and pulmonary arteries in rats without exposure of organs and with spatial resolution in the micrometer range and temporal resolution in the millisecond range. We have refined the system continually in terms of the spatial resolution and exposure time. X-rays transmitted through an object are detected by an X-ray direct-conversion type detector, which incorporates an X-ray SATICON pickup tube. The spatial resolution has been improved to 6 μm, yielding sharp images of small arteries. The exposure time has been shortened to around 2 ms using a new rotating-disk X-ray shutter, enabling imaging of beating rat hearts. Quantitative evaluations of the X-ray intravital microscopy technique were extracted from measurements of the smallest-detectable vessel size and detection of the vessel function. The smallest-diameter vessel viewed for measurements is determined primarily by the concentration of iodinated contrast material. The iodine concentration depends on the injection technique. We used ex vivo rat hearts under Langendorff perfusion for accurate evaluation. After the contrast agent is injected into the origin of the aorta in an isolated perfused rat heart, the contrast agent is delivered directly into the coronary arteries with minimum dilution. The vascular internal diameter response of coronary arterial circulation is analyzed to evaluate the vessel function. Small blood vessels of more than about 50 μm diameters were visualized clearly at heart rates of around 300 beats/min. Vasodilation compared to the control was observed quantitatively using drug manipulation. Furthermore, the apparent increase in the number of small vessels with diameters of less than about 50 μm was observed after the vasoactive agents increased the diameters of invisible small blood vessels to visible sizes. This technique is expected to offer the potential for direct investigation of mechanisms of vascular dysfunctions.

Synchrotron radiation imaging for advancing our understanding of cardiovascular function

Synchrotron radiation (SR) is increasingly being used for micro-level and nano-level functional imaging in in vivo animal experiments. This review focuses on the methodology that enables repeated and regional assessment of vessel internal diameter and flow in the resistance vessels of different organ systems. In particular, SR absorption microangiography approaches offer unique opportunities for real-time in vivo vascular imaging in small animals, even during dynamic motion of the heart and lungs. We also describe recent progress in the translation of multiple phase-contrast imaging techniques from ex vivo to in vivo small-animal studies. Furthermore, we also review the utility of SR for multiple pinpoint (dimensions 0.2×0.2 mm) assessments of myocardial function at the cross-bridge level in different regions of the heart using small-angle X-ray scattering, resulting from increases in SR flux at modern facilities. Finally, we present cases for the use of complementary SR approaches to study cardiovascular function, particularly the pathological changes associated with disease using small-animal models.