Altered myocardial microvascular 3D architecture in experimental hypercholesterolemia

Co-Registration of Peripheral Atherosclerotic Plaques Assessed by Conventional CT Angiography, MicroCT and Histology in Patients with Chronic Limb Threatening Ischaemia

OBJECTIVE

To co-register conventional computed tomography angiography (CTA), with ex vivo micro-computed tomography (microCT) and histology of popliteal atherosclerotic plaques. Improving the non-invasive imaging capabilities may be valuable to advance patient care with peripheral arterial obstructive disease towards lesion and individual based treatment.

METHODS

In this prospective observational study, 12 popliteal arteries from 11 symptomatic patients who had undergone transfemoral amputations for chronic limb threatening ischaemia and who had pre-operative CTA, were analysed ex vivo by microCT and histology. A total of 353 histological cross sections were co-registered with microCT and CTA, and classified as: lipid rich (LP, n = 26), fibrous (FP, n = 80), or calcific (CP, n = 247) plaques. CTA and microCT plaque density was calculated in 791 regions of interest as Hounsfield units (HU).

RESULTS

CTA and microCT could identify plaque components that were confirmed by histology such as fibrous tissue (FP), lipid pool/core (LP), and calcification (CP). MicroCT densities were 77.8 HU for FP (IQR 52.8, 129.5 HU), -28.4 HU for LP (IQR -87.1, 13.2 HU), and 3826.0 HU for CP (IQR 2989.0, 4501.0 HU). CTA densities of the three components of the plaque were: 78.0 HU for FP (IQR 59.5, 119.8 HU), 32.5 HU for LP (IQR 15.0, 42 HU), and 641.5 HU for CP (IQR 425.8, 1135 HU). The differences were statistically significant between the HU densitometric characteristics among the three groups (p < .0001) for both imaging modalities. Overall, microCT performed better diagnostically than conventional CTA for the three types of plaques: areas under the receiving operator characteristics curve were greater for microCT than CTA for FP (0.97 vs. 0.90), for LP (0.88 vs. 0.67), and for CP (0.97 vs. 0.90).

CONCLUSION

CTA and microCT can be used to identify histological atherosclerotic plaque components, with better diagnostic performance for microCT. This study demonstrates the feasibility of using microCT to assess plaque morphology lesions in a manner that approaches histology thus becoming a useful tool for ex vivo assessment of atherosclerosis and towards lesion based treatment.

Ossabaw Pigs With a PCSK9 Gain-of-Function Mutation Develop Accelerated Coronary Atherosclerotic Lesions: A Novel Model for Preclinical Studies

BACKGROUND

Ossabaw pigs are unique miniature swine with genetic predisposition to develop metabolic syndrome and coronary atherosclerosis after extended periods receiving atherogenic diets. We have hypothesized that transgenic Ossabaw swine expressing chimp PCSK9 (proprotein convertase subtilisin-like/kexin type 9) containing the D374Y gain of function would develop familial hypercholesterolemia and coronary artery plaques more rapidly than Landrace swine with the same transgene.

METHODS AND RESULTS

Ossabaw and Landrace PCSK9 gain-of-function founders were generated by Sleeping Beauty transposition and cloning. Histopathologic findings in the Ossabaw founder animal showed more advanced plaques and higher stenosis than in the Landrace founder, underscoring the Ossabaw genetic predisposition to atherosclerosis. We chose to further characterize the Ossabaw PCSK9 gain-of-function animals receiving standard or atherogenic diets in a 6-month longitudinal study using computed tomography, magnetic resonance (MR) imaging, intravascular ultrasound, and optical coherence tomography, followed by pathological analysis of atherosclerosis focused on the coronary arteries. The Ossabaw model was consistently hypercholesterolemic, with or without dietary challenge, and by 6 months had consistent and diffuse fibrofatty or fibroatheromatous plaques with necrosis, overlying fibrous caps, and calcification in up to 10% of coronary plaques.

CONCLUSIONS

The Ossabaw PCSK9 gain-of-function model provides consistent and robust disease development in a time frame that is practical for use in preclinical therapeutic evaluation to drive innovation. Although no animal model perfectly mimics the human condition, this genetic large-animal model is a novel tool for testing therapeutic interventions in the context of developing and advanced coronary artery disease.

A mathematical model of coronary blood flow control: simulation of patient-specific three-dimensional hemodynamics during exercise

This work presents a mathematical model of the metabolic feedback and adrenergic feedforward control of coronary blood flow that occur during variations in the cardiac workload. It is based on the physiological observations that coronary blood flow closely follows myocardial oxygen demand, that myocardial oxygen debts are repaid, and that control oscillations occur when the system is perturbed and so are phenomenological in nature. Using clinical data, we demonstrate that the model can provide patient-specific estimates of coronary blood flow changes between rest and exercise, requiring only the patient's heart rate and peak aortic pressure as input. The model can be used in zero-dimensional lumped parameter network studies or as a boundary condition for three-dimensional multidomain Navier-Stokes blood flow simulations. For the first time, this model provides feedback control of the coronary vascular resistance, which can be used to enhance the physiological accuracy of any hemodynamic simulation, which includes both a heart model and coronary arteries. This has particular relevance to patient-specific simulation for which heart rate and aortic pressure recordings are available. In addition to providing a simulation tool, under our assumptions, the derivation of our model shows that β-feedforward control of the coronary microvascular resistance is a mathematical necessity and that the metabolic feedback control must be dependent on two error signals: the historical myocardial oxygen debt, and the instantaneous myocardial oxygen deficit.

Bioengineering Human Myocardium on Native Extracellular Matrix

RATIONALE

More than 25 million individuals have heart failure worldwide, with ≈4000 patients currently awaiting heart transplantation in the United States. Donor organ shortage and allograft rejection remain major limitations with only ≈2500 hearts transplanted each year. As a theoretical alternative to allotransplantation, patient-derived bioartificial myocardium could provide functional support and ultimately impact the treatment of heart failure.

OBJECTIVE

The objective of this study is to translate previous work to human scale and clinically relevant cells for the bioengineering of functional myocardial tissue based on the combination of human cardiac matrix and human induced pluripotent stem cell-derived cardiomyocytes.

METHODS AND RESULTS

To provide a clinically relevant tissue scaffold, we translated perfusion-decellularization to human scale and obtained biocompatible human acellular cardiac scaffolds with preserved extracellular matrix composition, architecture, and perfusable coronary vasculature. We then repopulated this native human cardiac matrix with cardiomyocytes derived from nontransgenic human induced pluripotent stem cells and generated tissues of increasing 3-dimensional complexity. We maintained such cardiac tissue constructs in culture for 120 days to demonstrate definitive sarcomeric structure, cell and matrix deformation, contractile force, and electrical conduction. To show that functional myocardial tissue of human scale can be built on this platform, we then partially recellularized human whole-heart scaffolds with human induced pluripotent stem cell-derived cardiomyocytes. Under biomimetic culture, the seeded constructs developed force-generating human myocardial tissue and showed electrical conductivity, left ventricular pressure development, and metabolic function.

CONCLUSIONS

Native cardiac extracellular matrix scaffolds maintain matrix components and structure to support the seeding and engraftment of human induced pluripotent stem cell-derived cardiomyocytes and enable the bioengineering of functional human myocardial-like tissue of multiple complexities.

Measurement and modeling of coronary blood flow

Ischemic heart disease that comprises both coronary artery disease and microvascular disease is the single greatest cause of death globally. In this context, enhancing our understanding of the interaction of coronary structure and function is not only fundamental for advancing basic physiology but also crucial for identifying new targets for treating these diseases. A central challenge for understanding coronary blood flow is that coronary structure and function exhibit different behaviors across a range of spatial and temporal scales. While experimental studies have sought to understand this feature by isolating specific mechanisms, in tandem, computational modeling is increasingly also providing a unique framework to integrate mechanistic behaviors across different scales. In addition, clinical methods for assessing coronary disease severity are continuously being informed and updated by findings in basic physiology. Coupling these technologies, computational modeling of the coronary circulation is emerging as a bridge between the experimental and clinical domains, providing a framework to integrate imaging and measurements from multiple sources with mathematical descriptions of governing physical laws. State-of-the-art computational modeling is being used to combine mechanistic models with data to provide new insight into coronary physiology, optimization of medical technologies, and new applications to guide clinical practice.

Evaluation of coronary adventitial vasa vasorum using 3D optical coherence tomography--animal and human studies

Objectives

This study sought to evaluate adventitial vasa vasorum (VV) in vivo with novel imaging technique of optical coherence tomography (OCT).

Methods

To verify OCT methods for quantification of VV, we first studied 2 swine carotid arteries in a model of focal angiogenesis by autologous blood injection, and compared microchannel volume (MCV) by OCT and VV by m-CT, and counts of those. In OCT images, adventitial MC was identified as signal-voiding areas which were located within 1 mm from the lumen-intima border. After manually tracing microchannel areas and the boundaries of lumen-intima and media-adventitial in all slices, we reconstructed 3D images. Moreover, we performed with OCT imaging in 8 recipients referred for evaluation of cardiac allograft vasculopathy at 1 year after heart transplantation. MCV and plaque volume (PV) were assessed with 3D images in each 10-mm-segment.

Results

In the animal study, among the 16 corresponding 1-mm-segments, there were significant correlations of count and volume between both the modalities (count r²=0.80, P<0.01; volume r² =0.50, P<0.01) and a good agreement with a systemic bias toward underestimation with m-CT. In the human study, there was a significant positive correlation between MCV and PV (segment number=24, r² =0.63, P<0.01).

Conclusion

Our results suggest that evaluation of MCV with 3D OCT imaging might be a novel method to estimate the amount of adventitial VV in vivo, and further has the potential to provide a pathophysiological insight into a role of the VV in allograft vasculopathy.

Mesenchymal Stromal Cells Improve Renovascular Function in Polycystic Kidney Disease

Polycystic kidney disease (PKD) is a common cause of end-stage renal failure, for which there is no accepted treatment. Progenitor and stem cells have been shown to restore renal function in a model of renovascular disease, a disease that shares many features with PKD. The objective of this study was to examine the potential of adult stem cells to restore renal structure and function in PKD. Bone marrow-derived mesenchymal stromal cells (MSCs, 2.5 × 10(5)) were intrarenally infused in 6-week-old PCK rats. At 10 weeks of age, PCK rats had an increase in systolic blood pressure (SBP) versus controls (126.22 ± 2.74 vs. 116.45 ± 3.53 mmHg, p < 0.05) and decreased creatinine clearance (3.76 ± 0.31 vs. 6.10 ± 0.48 µl/min/g, p < 0.01), which were improved in PKD animals that received MSCs (SBP: 114.67 ± 1.34 mmHg, and creatinine clearance: 4.82 ± 0.24 µl/min/g, p = 0.001 and p = 0.003 vs. PKD, respectively). MSCs preserved vascular density and glomeruli diameter, measured using microcomputed tomography. PCK animals had increased urine osmolality (843.9 ± 54.95 vs. 605.6 ± 45.34 mOsm, p < 0.01 vs. control), which was improved after MSC infusion and not different from control (723.75 ± 56.6 mOsm, p = 0.13 vs. control). Furthermore, MSCs reduced fibrosis and preserved the expression of proangiogenic molecules, while cyst size and number were unaltered by MSCs. Delivery of exogenous MSCs improved vascular density and renal function in PCK animals, and the benefit was observed up to 4 weeks after a single infusion. Cell-based therapy constitutes a novel approach in PKD.

High-resolution micro-CT scanning as an innovative tool for evaluating dental hard tissue development

Microcomputerized tomography (micro‐CT) allows discriminating very small changes in dental hard tissue volumes. The aim of the present study was to create a new method for obtaining high‐resolution, three‐dimensional images of dental hard tissue development using micro‐CT, and to observe the changes in dental hard tissue development and composition in growing rat pups. Tooth germs from rats at the end of the 20‐day embryonic period (E20) and during the neonatal period (D1‐14) were subjected to micro‐CT. Three‐dimensional reconstructions were analyzed to compare dental hard tissue formation and mineralization during the different development periods. Scanning electron microscopy and energy dispersive spectroscopy were used to confirm mineral density (MD). Dental hard tissue began to form during the E20, but the process was slow and resulted in minimal deposition. Hard tissue volume increased by approximately 0.040 mm³/day from E20 to D3, and by 0.12‐0.42 mm³/day after D3, peaking at 0.42 mm³/day at D12. This increase in hard tissue volume resulted in continuous increases in hard tissue thickness, from 90.0 ± 20.7 μm at E20 to 545.2 ± 14.1 μm by D14. MD was 298 ± 3.1 mg HA/cm at E20 and increased to 678.2 ± 6.1 mg HA/cm by D14. The degree of calcification also progressively increased during the first 14 days of development. Dental MD was strongly associated with calcification. This study indicates that micro‐CT is a nondestructive, high‐resolution, reliable, and innovative tool for the evaluation of volume and MD of dental hard tissues during development. Micro‐CT minimizes artifacts caused by sample preparation.

PACS number: 87

Obesity-metabolic derangement exacerbates cardiomyocyte loss distal to moderate coronary artery stenosis in pigs without affecting global cardiac function

Obesity associated with metabolic derangements (ObM) worsens the prognosis of patients with coronary artery stenosis (CAS), but the underlying cardiac pathophysiologic mechanisms remain elusive. We tested the hypothesis that ObM exacerbates cardiomyocyte loss distal to moderate CAS. Obesity-prone pigs were randomized to four groups (n = 6 each): lean-sham, ObM-sham, lean-CAS, and ObM-CAS. Lean and ObM pigs were maintained on a 12-wk standard or atherogenic diet, respectively, and left circumflex CAS was then induced by placing local-irritant coils. Cardiac structure, function, and myocardial oxygenation were assessed 4 wk later by computed-tomography and blood oxygenation level dependent (BOLD) MRI, the microcirculation with micro-computed-tomography, and injury mechanisms by immunoblotting and histology. ObM pigs showed obesity, dyslipidemia, and insulin resistance. The degree of CAS (range, 50-70%) was similar in lean and ObM pigs, and resting myocardial perfusion and global cardiac function remained unchanged. Increased angiogenesis distal to the moderate CAS observed in lean was attenuated in ObM pigs, which also showed microvascular dysfunction and increased inflammation (M1-macrophages, TNF-α expression), oxidative stress (gp91), hypoxia (BOLD-MRI), and fibrosis (Sirius-red and trichrome). Furthermore, lean-CAS showed increased myocardial autophagy, which was blunted in ObM pigs (downregulated expression of unc-51-like kinase-1 and autophagy-related gene-12; P < 0.05 vs. lean CAS) and associated with marked apoptosis. The interaction diet xstenosis synergistically inhibited angiogenic, autophagic, and fibrogenic activities. ObM exacerbates structural and functional myocardial injury distal to moderate CAS with preserved myocardial perfusion, possibly due to impaired cardiomyocyte turnover.

Polycystic kidneys have decreased vascular density: a micro-CT study

OBJECTIVE

Polycystic kidney disease (PKD) is a common cause of end-stage renal failure and many of these patients suffer vascular dysfunction and hypertension. It remains unclear whether PKD is associated with abnormal microvascular structure. Thus, this study examined the renovascular structure in PKD.

METHODS

PKD rats (PCK model) and controls were studied at 10 weeks of age, and mean arterial pressure (MAP), renal blood flow, and creatinine clearance were measured. Microvascular architecture and cyst number and volume were assessed using micro-computed tomography, and angiogenic pathways evaluated.

RESULTS

Compared with controls, PKD animals had an increase in MAP (126.4 ± 4.0 vs. 126.2 ± 2.7 mmHg) and decreased clearance of creatinine (0.39 ± 0.09 vs. 0.30 ± 0.05 mL/min), associated with a decrease in microvascular density, both in the cortex (256 ± 22 vs. 136 ± 20 vessels per cm2) and medullar (114 ± 14 vs. 50 ± 9 vessels/cm2) and an increase in the average diameter of glomeruli (104.14 ± 2.94 vs. 125.76 ± 9.06 mm). PKD animals had increased fibrosis (2.2 ± 0.2 fold vs. control) and a decrease in the cortical expression in hypoxia inducible factor 1-α and vascular endothelial growth factor.

CONCLUSIONS

PKD animals have impaired renal vascular architecture, which can have significant functional consequences. The PKD microvasculature could represent a therapeutic target to decrease the impact of this disease.

Cardiac micro-computed tomography imaging of the aging coronary vasculature

BACKGROUND

Alterations at the level of the coronary circulation with aging may play an important role in the evolution of age-associated changes in left ventricular (LV) fibrosis and function. However these age-associated changes in the coronary vasculature remain poorly defined primarily due to the lack of high resolution imaging technologies. The current study was designed to utilize cardiac micro-computed tomography (micro-CT) technology as a novel imaging strategy, to define the 3-dimensional coronary circulation in the young and aged heart and its relationship to LV fibrosis and function.

METHODS AND RESULTS

Young (2 months old; n=10) and aged (20 months old; n=10) Fischer rats underwent cardiac micro-CT imaging as well as echocardiography, blood pressure, and fibrosis analysis. Importantly, when indexed to LV mass, which increased with age, the total and intramyocardial vessel volumes were lower, whereas the epicardial vessel volume, with and without indexing to LV mass, was significantly higher in the aged hearts compared with the young hearts. Moreover, the aged hearts had a significantly lower percentage of intramyocardial vessel volume and a significantly higher percentage of epicardial vessel volume, when normalized to the total vessel volume, compared with the young hearts. Further, the aged hearts had significant LV fibrosis and mild LV dysfunction compared with the young hearts.

CONCLUSIONS

This micro-CT imaging study reports the reduction in normalized intramyocardial vessel volume within the aged heart, in association with increased epicardial vessel volume, in the setting of increased LV fibrosis, and mild LV dysfunction.

Transition from obesity to metabolic syndrome is associated with altered myocardial autophagy and apoptosis

OBJECTIVE

Transition from obesity to metabolic-syndrome (MetS) promotes cardiovascular diseases, but the underlying cardiac pathophysiological mechanisms are incompletely understood. We tested the hypothesis that development of insulin resistance and MetS is associated with impaired myocardial cellular turnover.

METHODS AND RESULTS

MetS-prone Ossabaw pigs were randomized to 10 weeks of standard chow (lean) or to 10 (obese) or 14 (MetS) weeks of atherogenic diet (n=6 each). Cardiac structure, function, and myocardial oxygenation were assessed by multidetector computed-tomography and Blood Oxygen Level-Dependent-MRI, the microcirculation with microcomputed-tomography, and injury mechanisms by immunoblotting and histology. Both obese and MetS showed obesity and dyslipidemia, whereas only MetS showed insulin resistance. Cardiac output and myocardial perfusion increased only in MetS, yet Blood Oxygen Level-Dependent-MRI showed hypoxia. Inflammation, oxidative stress, mitochondrial dysfunction, and fibrosis also increased in both obese and MetS, but more pronouncedly in MetS. Furthermore, autophagy in MetS was decreased and accompanied by marked apoptosis.

CONCLUSIONS

Development of insulin resistance characterizing a transition from obesity to MetS is associated with progressive changes of myocardial autophagy, apoptosis, inflammation, mitochondrial dysfunction, and fibrosis. Restoring myocardial cellular turnover may represent a novel therapeutic target for preserving myocardial structure and function in obesity and MetS.

Retrograde perfusion and filling of mouse coronary vasculature as preparation for micro computed tomography imaging

Visualization of the vasculature is becoming increasingly important for understanding many different disease states. While several techniques exist for imaging vasculature, few are able to visualize the vascular network as a whole while extending to a resolution that includes the smaller vessels. Additionally, many vascular casting techniques destroy the surrounding tissue, preventing further analysis of the sample. One method which circumvents these issues is micro-Computed Tomography (μCT). μCT imaging can scan at resolutions <10 microns, is capable of producing 3D reconstructions of the vascular network, and leaves the tissue intact for subsequent analysis (e.g., histology and morphometry). However, imaging vessels by ex vivo μCT methods requires that the vessels be filled with a radiopaque compound. As such, the accurate representation of vasculature produced by μCT imaging is contingent upon reliable and complete filling of the vessels. In this protocol, we describe a technique for filling mouse coronary vessels in preparation for μCT imaging. Two predominate techniques exist for filling the coronary vasculature: in vivo via cannulation and retrograde perfusion of the aorta (or a branch off the aortic arch), or ex vivo via a Langendorff perfusion system. Here we describe an in vivo aortic cannulation method which has been specifically designed to ensure filling of all vessels. We use a low viscosity radiopaque compound called Microfil which can perfuse through the smallest vessels to fill all the capillaries, as well as both the arterial and venous sides of the vascular network. Vessels are perfused with buffer using a pressurized perfusion system, and then filled with Microfil. To ensure that Microfil fills the small higher resistance vessels, we ligate the large branches emanating from the aorta, which diverts the Microfil into the coronaries. Once filling is complete, to prevent the elastic nature of cardiac tissue from squeezing Microfil out of some vessels, we ligate accessible major vascular exit points immediately after filling. Therefore, our technique is optimized for complete filling and maximum retention of the filling agent, enabling visualization of the complete coronary vascular network--arteries, capillaries, and veins alike.

Simvastatin preserves diastolic function in experimental hypercholesterolemia independently of its lipid lowering effect

OBJECTIVE

Isolated diastolic dysfunction is present in 40% of heart failure patients. It has been attributed to myocardial fibrosis and related to cardiovascular risk factor exposure. We hypothesized that simvastatin will improve these dynamics in experimental hypercholesterolemia (HC).

METHODS

Three groups of pigs were studied after 12 weeks of normal (N) diet, HC diet, or HC diet with simvastatin (80 mg/day) treatment. Cardiac function was assessed by electron beam computed tomography (EBCT) and percentage of myocardium occupied by microvessels (myocardial vascular fraction) was calculated by micro-CT. Collagen content was determined by Sirius red staining and confirmed by a quantitative, hydroxyoproline-based assay.

RESULTS

Compared with N, LDL serum concentration was higher in HC and HC+simvastatin (1.0±0.1 vs. 7.9±1.7 and 9.6±1.2 mmol/L, p<0.05 for both). Cardiac early diastolic filling was reduced in HC compared with N (102.4±11.3 vs. 151.1±12.1 mL/s; p<0.05) but restored in HC+simvastatin (176.8±21.3 mL/s, p<0.05 vs. HC). Compared with N, myocardial vascular fraction was higher in HC but not in HC+simvastatin (1.98±0.84 vs. 4.48±0.31 and 2.95±0.95%; p<0.05 for HC vs. N). Myocardial collagen content was higher in HC than in HC+simvastatin and N (4.72±1.03 vs. 1.62±0.12 and 1.21±0.24% area staining; p<0.05 for HC vs. N), which was attributable mainly to an increase in collagen III (2.90±0.48 vs. 1.62±0.12 and 1.21±0.24% area staining; p<0.05 for HC vs. N).

CONCLUSIONS

Simvastatin is able to prevent diastolic dysfunction in experimental HC independent of its lipid lowering effect. This beneficial effect is, at least partially, due to a decrease in myocardial fibrosis and angiogenesis.

Novel use of X-ray micro computed tomography to image rat sciatic nerve and integration into scaffold

This paper describes how specimens of nervous tissue can be prepared for successful imaging in X-ray Micro Computed Tomography (microCT), and how this method can be used to study the integration of nervous tissue into a polymeric scaffold. The sample preparation involves staining the biological tissue with osmium tetroxide to increase its X-ray attenuation, and a technique for maintaining the specimen in a moist environment during the experiment to prevent drying and shrinkage. Using this method it was possible to observe individual nerve fascicles and their relationship to the 3-D tissue structure. A scaffold supporting a regenerated sciatic nerve was similarly stained to distinguish the nervous tissue from the scaffold, and to observe how the nerve grew through a 2.5 mm long, 100 microm x 100 microm cross-section channel polyimide array. Furthermore, blood vessels could be identified in these images, and it was possible to monitor how a large proximal blood vessel split through the channel scaffold and proceeded down individual channels. This paper explains how microCT is a useful tool both for studying the location and extent of growth into a polymeric scaffold, and for determining whether the regenerated tissue has blood supply.

Acute subepicardial infarction associated with severe septic shock--insight in myocardial perfusion

Isolated infarctions of the subepicardial myocardium without changes in subendocardium are extremely rare. We present an autoptic case with an acute subepicardial infarction of the right- and left-ventricular myocardium. A 53-year-old male was admitted to hospital with acute upper abdominal pain. Clinical examination revealed an acute infero-lateral myocardial infarction. The patient succumbed to acute heart failure a few hours later. Autopsy revealed numerous pulmonary abscesses due to suppurative lobular pneumonia with consecutive pericardial effusion. Furthermore, we diagnosed an acute myocardial infarct encompassing the entire right and left ventricles but limited to the subepicardial myocardium only. Microscopically, we observed fibrin microemboli in the subepicardial microvessels. The existence of an isolated subepicardial myocardial infarct challenges our understanding of myocardial perfusion.

Monocyte chemoattractant proteins mediate myocardial microvascular dysfunction in swine renovascular hypertension

BACKGROUND

Monocyte chemoattractant proteins (MCPs) play an important role in mediating inflammatory processes. Hypertension (HTN) is associated with inflammation as well as impaired cardiac microcirculatory function and structure, but the contribution of MCPs to these alterations remained unclear. This study tested the hypothesis that MCPs regulate cardiac microvascular function and structure in experimental HTN.

METHODS AND RESULTS

Pigs (n=6 per group) were studied after 10 weeks of normal, renovascular HTN, or renovascular HTN+ bindarit (MCPs inhibitor, 50 mg/kg/d PO). Left ventricular (LV) function, myocardial microvascular permeability, and fractional vascular volume were assessed by fast computed tomography before and after adenosine infusion (400 microg/kg/min). Myocardial fibrosis, inflammation, and microvascular remodeling were determined ex vivo. Hypertension was not altered by bindarit, but LV hypertrophy and diastolic function were improved. In response to adenosine, myocardial microvascular permeability increased in HTN (from 0.0083+/-0.0009 to 0.0103+/-0.0011 AU, P=0.038 versus baseline) and fractional vascular volume decreased, whereas both remained unchanged in normal and HTN+bindarit pigs. HTN upregulated endothelin-1 expression, myocardial inflammation, and microvascular wall thickening, which were inhibited by bindarit.

CONCLUSIONS

MCPs partly mediate myocardial inflammation, fibrosis, vascular remodeling, and impaired vascular integrity induced by hypertension. Inhibition of MCPs could potentially be a therapeutic target in hypertensive cardiomyopathy.

Myocardial microvascular function during acute coronary artery stenosis: effect of hypertension and hypercholesterolaemia

AIMS

Coronary collateral arteries (CCA) reduce cardiovascular events. We tested the hypothesis that new microvessels that proliferate in early atherosclerosis may be associated with myocardial protection during acute subtotal coronary artery obstruction (CAO).

METHODS AND RESULTS

Acute left anterior descending CAO was induced by a balloon catheter in pigs after 12 weeks of high-cholesterol (HC) diet, renovascular hypertension (HTN), or normal control. Cardiac structure, myocardial perfusion, and functional response to iv adenosine and CAO were studied in vivo using electron beam computed tomography (CT). The intra-myocardial microvessels were subsequently evaluated ex vivo using micro-CT, and myocardial expression of growth factors using immunoblotting. Basal myocardial perfusion and microvascular permeability were similar among the groups, whereas their responses to adenosine were attenuated in HC and HTN. A significant decline in myocardial perfusion in normal pigs during acute CAO was attenuated in HC and abolished in HTN. CAO also elicited an increase in normal anterior wall microvascular permeability (+202 +/- 59%, P < 0.05), which was attenuated in HC and HTN (+55 +/- 9 and +31 +/- 8%, respectively, P < 0.05 vs. normal). Microvascular (<200 microm) spatial density was significantly elevated in HC and HTN, accompanied by increased myocardial growth factor expression.

CONCLUSION

This study demonstrates that early exposure to the cardiovascular risk factors HC and HTN protects the heart from decreases in myocardial perfusion during acute subtotal CAO. This protective effect is associated with and potentially mediated by pre-emptive development of intra-myocardial microvessels that might serve as recruitable CCA.

Emergence of targeted molecular imaging in atherosclerotic cardiovascular disease

Atherosclerosis, a systemic disease, remains one of the leading causes of morbidity and mortality in the world. Our improved understanding of the molecular mechanisms underlying atherosclerotic lesion progression and sudden transformation into unstable plaques, indicate complex interactions of lipid metabolism, inflammatory processes and genetic predisposition. Currently, novel imaging approaches to visualize the process of atherosclerosis, particularly at the molecular level, are actively being developed. Important targets include inflammatory and endothelial cells, as well as apoptosis and angiogenesis. The next decade should solidify the role of targeted molecular imaging in all aspects of cardiovascular medicine.

Evaluation of angiogenesis using micro-computed tomography in a xenograft mouse model of lung cancer

Quantitative evaluation of lung tumor angiogenesis using immunohistochemical techniques has been limited by difficulties in generating reproducible data. To analyze intrapulmonary tumor angiogenesis, we used high-resolution micro-computed tomography (micro-CT) of lung tumors of mice inoculated with mouse Lewis lung carcinoma (LLC1) or human adenocarcinoma (A549) cell lines. The lung vasculature was filled with the radiopaque silicone rubber, Microfil, through the jugular vein (in vivo application) or pulmonary artery (ex vivo application). In addition, human adenocarcinoma lung tumor-bearing mice treated site-specifically with humanized monoclonal antibody (bevacizumab) against vascular endothelial growth factor. Quantitative analysis of lung tumor microvessels imaged with micro-CT showed that more vessels (mainly small, <0.02 mm(2)) were filled using the in vivo (5.4%) compared with the ex vivo (2.1%) method. Furthermore, bevacizumab-treated lung tumor-bearing mice showed significantly reduced lung tumor volume and lung tumor angiogenesis compared with untreated mice as assessed by micro-CT. Interestingly, microvascularization of mainly the smaller vessels (<0.02 mm(2)) was reduced after bevacizumab treatment. This observation with micro-CT was nicely correlated with immunohistochemical measurement of microvessels. Therefore, micro-CT is a novel method for investigating lung tumor angiogenesis, and this might be considered as an additional complementary tool for precise quantification of angiogenesis.

Virtual histology by means of high-resolution X-ray CT

Micro-CT is a non-destructive technique for 3D tomographic investigation of an object. A 3D representation of the internal structure is calculated based on a series of X-ray radiographs taken from different angles. The spatial resolution of current laboratory-used micro-CT systems has come down over the last years from a few tens of microns to a few microns. This opens the possibility to perform histological investigations in 3D on a virtual representation of a sample, referred to as virtual 3D histology. The advantage of micro-CT based virtual histology is the immediate and automated 3D visualization of the sample without prior slicing, sample preparation like decalcification, photographing and aligning. This not only permits a drastic reduction in preparation time but also offers the possibility to easily investigate objects that are difficult to slice. This article presents results that were obtained on punch biopsies of horse skin, (dental) alveolus of ponies and chondro-osseous samples from the tarsus of foals studied with the new high resolution micro-CT set-up (HRXCT) at the Ghent University (Belgium) (http://www.ugct.ugent.be). This state-of-the-art set-up provides a 1 micron resolution and is therefore ideally suited for a direct comparison with standard light microscopy-based histology.

Estimation of regional myocardial mass at risk based on distal arterial lumen volume and length using 3D micro-CT images

The determination of regional myocardial mass at risk distal to a coronary occlusion provides valuable prognostic information for a patient with coronary artery disease. The coronary arterial system follows a design rule which allows for the use of arterial branch length and lumen volume to estimate regional myocardial mass at risk. Image processing techniques, such as segmentation, skeletonization and arterial network tracking, are presented for extracting anatomical details of the coronary arterial system using micro-computed tomography (micro-CT). Moreover, a method of assigning tissue voxels to their corresponding arterial branches is presented to determine the dependent myocardial region. The proposed micro-CT technique was utilized to investigate the relationship between the sum of the distal coronary arterial branch lengths and volumes to the dependent regional myocardial mass using a polymer cast of a porcine heart. The correlations of the logarithm of the total distal arterial lengths (L) to the logarithm of the regional myocardial mass (M) for the left anterior descending (LAD), left circumflex (LCX) and right coronary (RCA) arteries were log(L)=0.73log(M)+0.09 (R=0.78), log(L)=0.82log(M)+0.05 (R=0.77) and log(L)=0.85log(M)+0.05 (R=0.87), respectively. The correlation of the logarithm of the total distal arterial lumen volumes (V) to the logarithm of the regional myocardial mass for the LAD, LCX and RCA were log(V)=0.93log(M)-1.65 (R=0.81), log(V)=1.02log(M)-1.79 (R=0.78) and log(V)=1.17log(M)-2.10 (R=0.82), respectively. These morphological relations did not change appreciably for diameter truncations of 600-1400microm. The results indicate that the image processing procedures successfully extracted information from a large 3D dataset of the coronary arterial tree to provide prognostic indications in the form of arterial tree parameters and anatomical area at risk.

Antioxidant vitamins induce angiogenesis in the normal pig kidney

The effects of chronic supplementation with antioxidant vitamins on angiogenesis are controversial. The aim of the present study was to evaluate in kidneys of normal pigs the effect of chronic supplementation with vitamins E and C, at doses that are effective in reducing oxidative stress and attenuating angiogenesis under pathological conditions. Domestic pigs were randomized to receive a 12-wk normal diet without ( n = 6) or with antioxidant vitamins supplementation (1g/day vitamin C, 100 IU·kg−1·day−1 vitamin E; n = 6). Electron beam computed tomography (CT) was used to evaluate renal cortical vascular function in vivo, and micro-CT was to assess the spatial density and average diameter of cortical microvessels (diameter <500 μm) ex vivo. Oxidative stress and expressions of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor (HIF)-1α were evaluated in renal tissue. The effects of increasing concentrations of the same vitamins on redox status and angiogenesis were also evaluated in human umbilical vascular endothelial cells (HUVEC). Compared with normal pigs, the density of cortical transmural microvessels was significantly greater in vitamin-supplemented pigs (149.0 ± 11.7 vs. 333.8 ± 48.1 vessel/cm2, P < 0.05), whereas the cortical perfusion response to ACh was impaired. This was accompanied by a significant increase in tissue oxidative stress and levels of VEGF and HIF-1α. A low dose of antioxidant decreased, whereas a high dose increased, HUVEC oxidative stress and angiogenesis, which was partly mediated by hydrogen peroxide. Antioxidant vitamin supplementation can increase tissue oxidative redox and microvascular proliferation in the normal kidney, probably due to a biphasic effect that depends on basal redox balance.

Impaired myocardial perfusion reserve in experimental hypercholesterolemia is independent of myocardial neovascularization

Our objective was to investigate the functional role of hypercholesterolemia-associated myocardial neovascularization in early atherosclerosis using the antiangiogenic thalidomide. Experimental atherosclerosis is characterized by myocardial neovascularization, associated with a decrease in myocardial perfusion response to challenge, coronary endothelial dysfunction, and high oxidative stress. However, the functional significance of these neovessels is not known. Three groups of pigs (n = 6 each) were studied after 12 wk of normal or hypercholesterolemic diet without (HC) or with thalidomide (HC + Thal). Myocardial perfusion and permeability were assessed at baseline and in response to cardiac challenge, using electron beam computed tomography, and coronary endothelial function was assessed using organ chambers. Myocardial samples were scanned ex vivo with a three-dimensional microscopic computed tomography scanner, and the spatial density of the myocardial microvessels was quantified. Growth factors and oxidative stress were measured in the myocardial tissue. As a results of these procedures, myocardial perfusion response to adenosine and dobutamine was blunted in both HC and HC + Thal pigs compared with normal pigs (P < 0.05, HC and HC + Thal vs. normal) as was the coronary endothelial function. Myocardial permeability response to adenosine was increased in both HC and HC + Thal pigs compared with normal pigs (P < 0.05, HC and HC + Thal vs. normal, and HC + Thal vs. HC). The microvascular density was increased in HC pigs compared with normal pigs but normalized in HC + Thal pigs (P < 0.001 HC vs. normal and HC + Thal). HC + Thal pigs showed decreased expression of Flk-1 and basic FGF but increased expression of VEGF compared with normal and HC pigs. Oxidative stress was increased in both HC and HC + Thal pigs compared with normal pigs. In conclusion, chronic administration of thalidomide attenuates myocardial neovascularization in experimental HC pigs without affecting myocardial perfusion response to stimulation. This suggests that the myocardial neovascularization may not contribute to the attenuated myocardial perfusion response in hypercholesterolemia.

Relation between branching patterns and perfusion in stochastic generated coronary arterial trees

Biological variation in branching patterns is likely to affect perfusion of tissue. To assess the fundamental consequences of branching characteristics, 50 stochastic asymmetrical coronary trees and one non-stochastic symmetrical branching tree were generated. In the stochastic trees, area growth, A, at branching points was varied: A = random; 1.00; 1.10; 1.13 and 1.15 and symmetry, S, was varied: S = random; 1.00; 0.70; 0.58; 0.50 and 0.48. With random S and A values, a large variation in flow and volume was found, linearly related to the number of vessels in the trees. Large A values resulted in high number of vessels and high flow and volume values, indicating vessels connected in parallel. Lowering symmetry values increased the number of vessels, however, without changing flow, indicating a dominant connection of vessels in series. Both large A and small S values gave more realistic gradual pressure drops compared to the symmetrical non-stochastic branching tree. This study showed large variations in tree realizations, which may reflect real biological variations in tree anatomies. Furthermore, perfusion of tissue clearly depends on the branching rules applied.

Atorvastatin affects several angiogenic mediators in human endothelial cells

The pleiotropic effects of statins, inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, have been recently extended to the modulation of angiogenesis. Here, to get more insight into the statins action, the authors have investigated the effect of atorvastatin on the expression of several angiogenic and inflammatory genes in human umbilical endothelial cells (HUVECs). Atorvastatin was proangiogenic at the dose of 10 nM, and antiangiogenic at the concentrations of 1 to 10 micro M. Moreover, these higher concentrations inhibited also the proliferation of HUVECs induced by vascular endothelial growth factor (VEGF). Lower doses of atorvastatin did not influence endothelial cell proliferation. Importantly, atorvastatin at the micromolar concentrations diminished the production of interleukin (IL)-8, a proinflammatory and proangiogenic chemokine, and inhibited the synthesis of urokinase plasminogen activator (uPA), a potent proinflammatory mediator. However, it decreased also the expression of plasminogen activator inhibitor-1 (PAI-1) and thrombospondin-1 (TSP-1), the inhibitors of angiogenesis. Atorvastatin stimulated the expression of angiopoietin (Ang)-2 and moderately enhanced the expression of endothelial nitric oxide synthase (eNOS), whereas heme oxygenase-1 (HO-1) was not significantly affected. In conclusion, the present findings points to other angiogenesis-related effects of atorvastatin, which may be of relevance to the beneficial influence of statins in cardiovascular system.

Three-dimensional imaging and morphometric analysis of alveolar tissue from microfocal X-ray-computed tomography

We evaluated microfocal X-ray-computed tomography (micro-CT) as a method to visualize lung architecture two and three dimensionally and to obtain morphometric data. Inflated porcine lungs were fixed by formaldehyde ventilation. Tissue samples (8-mm diameter, 10-mm height) were stained with osmium tetroxide, and 400 projection images (1,024 × 1,024 pixel) were obtained. Continuous isometric micro-CT scans (voxel size 9 μm) were acquired to reconstruct two- and three-dimensional images. Tissue samples were sectioned (8-μm thickness) for histological analysis. Alveolar surface density and mean linear intercept were assessed by stereology-based morphometry in micro-CT scans and corresponding histological sections. Furthermore, stereology-based morphometry was compared with morphometric semi-automated micro-CT analysis within the same micro-CT scan. Agreement of methods was assessed by regression and Bland-Altman analysis. Comparing histology with micro-CT, alveolar surface densities (35.4 ± 2.4 vs. 33.4 ± 1.9/mm, P < 0.05) showed a correlation ( r = 0.72; P = 0.018) with an agreement of 2 ± 1.6/mm; the mean linear intercept (135.7 ± 14.5 vs. 135.8 ± 15 μm) correlated well ( r = 0.97; P < 0.0001) with an agreement of −0.1 ± 3.4 μm. Semi-automated micro-CT analysis resulted in smaller alveolar surface densities (33.4 ± 1.9 vs. 30.5 ± 1/mm; P < 0.01) with a correlation ( r = 0.70; P = 0.023) and agreement of 2.9 ± 1.4/mm. Non-destructive micro-CT scanning offers the advantage to visualize the spatial tissue architecture of small lung samples two and three dimensionally.

Dyslipidaemia and microvascular disease in the retina

PURPOSE

There are few data on the effect of serum lipids on microvascular disease. This study assessed the relationships between serum lipid levels and microvascular disease, as seen in the retina, among participants who attended a population-based study in Australia (n=3654, aged 49+years).

METHODS

Diameters of retinal arterioles and venules were measured from digitised photographs of each participant to obtain an estimate of generalised arteriolar narrowing. Focal arteriolar narrowing, arteriovenous nicking, and retinopathy lesions (microaneurysms, haemorrhages, hard/soft exudates) were graded using a standard protocol. Fasting blood tests were performed in 89% of subjects. Adjusted means were calculated using general linear models. Logistic regression models were used to determine the odds ratios for retinal microvascular signs.

RESULTS

After controlling for age, sex, body mass index, smoking, and mean arterial blood pressure, elevated high-density lipoprotein cholesterol was associated with narrower retinal arterioles (Ptrend=0.002) and venules (Ptrend=0.03) and with increased odds of generalised arteriolar narrowing (odds ratio 1.6, 95% confidence interval 1.1-2.2 for the highest vs the lowest quintile of high-density lipoprotein cholesterol). Serum triglyceride had a U-shaped relationship with venular diameter (Ptrend=0.003). We found no consistent pattern of association between serum total cholesterol or low-density lipoprotein cholesterol and any retinal microvascular signs.

CONCLUSIONS

These findings suggest that microvascular disease in the retina may result from processes distinct from dyslipidaemia.

Functional and structural remodeling of the myocardial microvasculature in early experimental hypertension

Advanced hypertension (HT), associated with left ventricular hypertrophy (LVH), impairs myocardial microvascular function and structure and leads to increased myocardial hypoxia and growth factor activation. However, the effect of HT on microvascular architecture and its relation to microvascular function, before the development of LVH (early HT), remains unclear. By way of method, pigs were studied after 12 wk of renovascular HT (n = 7) or control (n = 7) animals. Myocardial microvascular function (blood volume and blood flow at baseline and in response to adenosine) was assessed by using electron beam computed tomography (CT). Microvascular architecture was subsequently studied ex vivo using micro-CT, and microvessels (diameter, <500 microm) were counted in situ in three-dimensional images (40-microm on-a-side cubic voxels). Myocardial expression of vascular endothelial growth factor, basic fibroblast growth factor, and hypoxia-inducible factor-1alpha were also measured. By way of results, left ventricular muscle mass was similar between the groups. The blood volume response to intravenous adenosine was attenuated in HT animals compared with normal animals (+7.4 +/- 17.0 vs. +46.2 +/- 12.3% compared with baseline, P = 0.48 and P = 0.01, respectively). Microvascular spatial density in HT animals was significantly elevated compared with normal animals (246 +/- 26 vs. 125 +/- 20 vessels/cm2, P < 0.05) and correlated inversely with the blood volume response to adenosine. Growth factors expression was increased in HT animals compared with control animals. In conclusion, early HT elicits changes in myocardial microvascular architecture, which are associated with microvascular dysfunction and precede changes in muscle mass. These observations underscore the direct and early effects of HT on the myocardial vasculature.

Myocardial ischemia and coronary microvascular vasomotion: the impact of hypercholesterolemia

Coronary microvascular dilation in response to myocardial ischemia is an important defense mechanism for minimizing heart injury. Since myocardial ischemia is an intense stimulus for a living body, many biologic signals that affect the vascular tone are activated. Recent evidence demonstrated that among them, ischemic myocardium-derived factors play dominant roles as mediators of ischemic vasodilation, and that ischemic myocardium releases vasoconstrictor signals simultaneously. Hypercholesterolemia, a major risk factor for coronary atherosclerosis, is known to produce microvascular dysfunction, although it does not produce atherosclerotic lesions at the microvascular level. A recent bioassay study demonstrated that the vasodilator signal transduction from the myocardium to coronary microvessels is severely impaired in hypercholesterolemia. It is likely that redox-sensitive mechanisms play a major role in the impairment of the defensive responses. The present understanding of the mechanism of ischemic vasodilation and the impact of hypercholesterolemia on coronary microvascular regulation shall be discussed in this review.

Acute Rat Lung Injury: Feasibility of Assessment with Micro-CT

PURPOSE

To evaluate the feasibility of micro-computed tomography (CT) for analysis of the lung fine structure and its alterations during endotoxin-induced lung injury.

MATERIALS AND METHODS

Intravital perfusion-fixed rat lungs with (n = 5) and without (n = 5) endotoxin perfusion were scanned with micro-CT. Three imaging modalities (conventional histology, intravital microscopy, and electron microscopy) were used to document the effect of endotoxin and the in vivo application of contrast agent (a mixture of barium sulfate, gelatin, and thymol). The effect of endotoxin on structural changes of the lung was evaluated with analysis of variance.

RESULTS

Intravital microscopy, conventional histology, and electron microscopy demonstrated capillary perfusion of contrast agent, inflated alveoli, and no extravasation of barium sulfate in the extravascular space. Systemic application of endotoxin led to a significant increase in the soft-tissue volume of the lungs (ie, tissue edema) (58.09 microm(3)+/- 4.6 [standard error of the mean] vs 8.31 microm(3)+/- 1.63, P <.001) and significant thickening of the alveolar walls (34.01 microm +/- 4.5 vs 14.83 microm +/- 2.5, P <.001) at micro-CT. Simultaneously, endotoxin-treated rat lungs showed a significant reduction in total air space (49.74 microm(3)+/- 1.72 vs 100.99 microm(3)+/- 1.16, P <.001).

CONCLUSION

These findings indicate that micro-CT is feasible for structural evaluation of the lung fine structure and its alterations during endotoxin-induced lung injury.

Adventitial vasa vasorum heterogeneity among different vascular beds

INTRODUCTION

Different vascular beds show substantial variation in their susceptibilities for development of vascular disease like atherosclerosis, and thereby exhibit a variety of different clinical presentations. Yet, the underlying mechanism of this heterogeneity is not well defined. Recent evidence suggests a role for the vasa vasorum (VV) in vascular disease. We hypothesized that there is a differential distribution structure of adventitial VV in different vascular beds. Hence, the current study was designed to characterize and compare the structure of the adventitial VV in the coronary and the peripheral circulation.

METHODS

Samples of vessels from different vascular beds were obtained from 6 female crossbred domestic pigs. The samples were scanned using micro-computed tomography, and the images reconstructed and analyzed to characterize VV architecture, including vessel wall area, VV count, VV density, intravessel spatial distribution, mean diameter of first- and second-order VVs and the ratio of second- to first-order VVs.

RESULTS

There were significant differences in VV density among different vascular beds. Density was highest in coronary arteries (2.91 +/- 0.26 vessels/mm2, P <.05, vs renal, carotid, and femoral arteries), intermediate in renal arteries (1.45+/- 0.22 vessels/mm2, P <.05, vs femoral artery) and carotid arteries (0.64 +/- 0.08 vessels/mm2, P <.05, vs femoral artery), and lowest in femoral arteries (0.23 +/- 0.05 vessels/mm2 ). A similar pattern for the ratio of second- to first-order VV was also observed. Random intravessel spatial distribution of VVs was seen in all vascular beds.

CONCLUSION

The current study demonstrates a differential structure of the adventitial VV in different vascular beds. This intra- and intervessel heterogeneity in VV anatomy is a phenotypic variability that might determine a differential local response to systemic risk factors and, thereby, variable propensity for vascular disease among different vascular beds.

[Cardio-pulmonary vascular system. Three-dimensional quantitative evaluation by microcomputed tomography]

In recent years microcomputed tomography (microCT) has become more and more important in basic research. Now commercial microCT scanners are available. Thus, it is very likely that this new, accurate and promising method for three-dimensional and non-destructive quantitative evaluation of intact tissues including vessels will be applied more frequently. The review provides a survey of the basic technology of microCT and its current use for high resolution three-dimensional morphometric and functional analysis within the cardio-pulmonary vascular system.

Quantitative microcomputed tomography analysis of collateral vessel development after ischemic injury

Transgenic mouse models are increasingly being used to investigate the functions of specific growth factors or matrix proteins to design therapeutic strategies for controlling blood vessel growth. However, the available methodologies for evaluating angiogenesis and arteriogenesis in these models are limited by animal size, user subjectivity, the power to visualize the three-dimensional vessel networks, or the capability to employ a vigorous quantitative analysis. In this study, we employed contrast-enhanced microcomputed tomography imaging to assess collateral development after induction of hindlimb ischemia in the mouse. The morphological parameters vessel volume, connectivity, number, thickness, thickness distribution, separation, and degree of anisotropy were evaluated in control and surgery limbs 0, 3, and 14 days postsurgery. Results indicate that the vascular volume of the surgically manipulated limb was reconstituted as early as 3 days after femoral artery excision through development of a series of highly connected, small caliber, closely spaced, and isotropically oriented collateral vessels. Parametric analyses were completed to assess the sensitivity of the calculated morphological parameters to variations in image binarization threshold and voxel size. Images taken at the 36-μm voxel size were found to be optimal for evaluating collateral vessel formation, whereas 8- to 16-μm voxel sizes were needed to resolve smaller vascular structures. This study demonstrates the utility of microcomputed tomography as a robust method for quantitative, three-dimensional analysis of blood vessel networks. Whereas these initial efforts focused on the mouse hindlimb ischemia model, the developed techniques may be applied to a variety of model systems to investigate mechanisms of angiogenesis and arteriogenesis.

Atherosclerotic lesions at micro CT: feasibility for analysis of coronary artery wall in autopsy specimens

PURPOSE

To evaluate the feasibility of micro computed tomography (CT) for analysis of the coronary artery wall.

MATERIALS AND METHODS

With micro CT, two-dimensional transverse images were generated from 10 human autopsy specimens of coronary arteries (2.5-3.5 cm long), with section thickness of 6 microm. Vessel wall perimeter, plaque area, calcified lesion area, media area, and lumen area were determined by three experienced radiologists. Results were compared with those obtained from a detailed conventional histomorphometric analysis of corresponding cross sections. Hotelling T(2) test (a multivariate generalization of the univariate Student t test) and Pearson correlation coefficient were used to assess the correlation between micro CT findings and conventional histologic measurements. The significance of differences in gray-scale measurements was tested with analysis of variance.

RESULTS

Micro CT provided quantitative information about plaque morphology equivalent to that provided with histomorphometric analysis. Hotelling T(2) test revealed significantly smaller values for vessel wall perimeter and lumen area with histologic sections (P <.001). Gray-scale measurements were established with which lesions could be categorized after histologic classification.

CONCLUSION

Micro CT is feasible for analysis of the coronary artery wall.

Analysis of the Fetal Placental Vascular Tree by X-ray Micro-computed Tomography

The current understanding of the placental vascular tree largely derives from time-consuming morphometric analyses performed by conventional histology, electron microscopy of corrosion casts and three-dimensional reconstructions based on physical tissue sections. In the present study, we demonstrate for the first time that micro-computed tomography (micro-CT) emerges as a new, non-destructive and fast tool for imaging and quantifying fetoplacental vasculature. Term placentae (n=5) were perfused with contrast agent consisting of barium-sulfate, gelatine and thymol shortly after Caesarean-section-delivery. Samples (1 cm(3)) from eight different regions of the placenta were subsequently scanned in a micro-CT. Using tomographic reconstruction algorithms, three dimensional images were obtained by micro-CT allowing total stereoscopic visualization and continuous quantitative analysis of the vascular structure of the investigated samples. These samples were compared regarding vascular surface (VS) and vascular density (vascular volume fraction, TCVF). Quantitative assessment showed an average vascular density of 16 per cent (SD+/-0.4) and a vascular surface of 475 mm(2)(SD+/-8) per total tissue volume (including intervillous space) of 125 mm(3). Micro-CT image-analysis showed no significant differences in the fetal vascularization among term placentae. Micro-CT imaging is feasible for imaging and analysis of the villous vascular tree, allows further morphologic studies and immunohistochemistry of the placental specimens and may emerge as an additional tool in the investigation of the physiology and pathophysiology of the placental vasculature.

Experimental microcomputed tomography study of the 3D microangioarchitecture of tumors

Differences between soft X-ray imaging and microcomputed tomography (micro-CT) in the microangiographic depiction of small vessels in tumors were compared to evaluate the tumors' 3D microangioarchitecture and the progress of growth-related neovascularization. VX2 carcinomas transplanted to the auricles of 24 rabbits randomly assigned to three groups were examined after 1, 3, and 7 days. Eight rabbits without transplants were the controls. Barium sulfate was injected into the auricular artery, and conventional soft X-ray images and micro-CT microangiograms of auricle specimens were studied. Micro-CT detected vessels with diameters of less than 50 microm, and imaging from several angles clearly showed the network of tumor vessels. Moreover, micro-CT confirmed the 3D process of growth-related neovascularization. There were no significant differences between the present findings and those of our previously published microscopic study. Micro-CT should prove useful for evaluating the 3D microarchitecture of tumors and for clear imaging of tumor angiogenesis.

The use of microcomputed tomography to study microvasculature in small rodents

Appropriate nephron function is dependent on the intrarenal arrangement of blood vessels. The preferred and primary means to study the architecture of intrarenal circulation has been by filling it with opaque substances such as india ink, radio-opaque contrast material, or various polymers for study by light or scanning electron microscopy. With such methodologies, superficial vessels may obscure deep vessels and little quantitative information may be obtained. Serial-section microtomy has not been practical because of problems relating to alignment and registration of adjacent sections, lost sections, and preparation time and effort. Microcomputed tomography (micro-CT) overcomes such limitations and provides a means to study the three-dimensional architecture of filled vessels within an intact rodent kidney and to obtain more quantitative information. As an example of micro-CT's capabilities, we review the use of micro-CT to study the alterations in renal microvasculature caused by the development of liver cirrhosis after chronic bile duct ligation. In this example, micro-CT evidence shows a selective decrease in cortical vascular filling in the kidney, with a maintenance of medullary vascular filling. These changes may contribute to the salt and water retention that accompanies cirrhosis. These results indicate that micro-CT is a promising method to evaluate renal vascular architecture in the intact rodent kidney relative to physiological and pathological function.

Enhanced renal cortical vascularization in experimental hypercholesterolemia

BACKGROUND

Experimental hypercholesterolemia is associated with pro-inflammatory changes and impaired regulation of tissue perfusion, which may lead to neovascularization. However, it is yet unknown whether such changes take place in the kidney. In this study, using a novel three-dimensional (3-D) micro computed-tomography technique we tested the hypothesis that hypercholesterolemia was associated with increased microvascular density in the renal cortex.

METHODS

Kidneys were excised from pigs after 12 weeks of either a normal (N = 6) or high cholesterol (HC; N = 5) diet, histology slides processed, and a segmental renal artery injected with a radio-opaque intravascular silicone polymer. Renal samples were scanned with micro computed-tomography, transverse and three-dimensional images were reconstructed, and microvessels (80 to 360 microm in diameter) counted in situ.

RESULTS

Serum cholesterol levels were significantly higher in hypercholesterolemic compared to normal pigs (383 +/- 76 vs. 81 +/- 7 mg/dL, P < 0.01), and microvascular spatial density was significantly higher in their inner and middle renal cortex (189 +/- 7 vs. 126 +/- 6 microvessels/cm2, P < 0.0001). Hypercholesterolemic kidneys also showed mild interstitial mononuclear infiltration and heavier immunostaining of vascular endothelial growth factor, but no other signs of morphological damage.

CONCLUSIONS

These results demonstrate that early diet-induced hypercholesterolemia is associated with increased microvascular density in the renal cortex, which precedes signs of overt renal morphological damage. These alterations may potentially affect regulation and/or spatial distribution of intrarenal blood flow in hypercholesterolemia, and may participate in renal disease progression.

Involvement of oxidation-sensitive mechanisms in the cardiovascular effects of hypercholesterolemia

Hypercholesterolemia is a common clinical metabolic and/or genetic disorder that promotes functional and structural vascular wall injury. The underlying mechanisms for these deleterious effects involve a local inflammatory response and release of cytokines and growth factors. Consequent activation of oxidation-sensitive mechanisms in the arterial wall, modulation of intracellular signaling pathways, increased oxidation of low-density lipoprotein cholesterol, and quenching of nitric oxide can all impair the functions controlled by the vascular wall and lead to the development of atherosclerosis. This cascade represents a common pathological mechanism activated by various cardiovascular risk factors and may partly underlie synergism among them as well as the early pathogenesis of atherosclerosis. Antioxidant intervention and restoration of the bioavailability of nitric oxide have been shown to mitigate functional and structural arterial alterations and improve cardiovascular outcomes. Elucidation of the precise nature and role of early transductional signaling pathways and transcriptional events activated in hypercholesterolemia in children and adults, including mothers during pregnancy, and understanding their downstream effects responsible for atherogenesis may help in directing preventive and interventional measures against atherogenesis and vascular dysfunction.