Capillary rarefaction: a missing link in renal and cardiovascular disease?

Patients with chronic kidney disease (CKD) have an increased risk for cardiovascular morbidity and mortality. Capillary rarefaction may be both one of the causes as well as a consequence of CKD and cardiovascular disease. We reviewed the published literature on human biopsy studies and conclude that renal capillary rarefaction occurs independently of the cause of renal function decline. Moreover, glomerular hypertrophy may be an early sign of generalized endothelial dysfunction, while peritubular capillary loss occurs in advanced renal disease. Recent studies with non-invasive measurements show that capillary rarefaction is detected systemically (e.g., in the skin) in individuals with albuminuria, as sign of early CKD and/or generalized endothelial dysfunction. Decreased capillary density is found in omental fat, muscle and heart biopsies of patients with advanced CKD as well as in skin, fat, muscle, brain and heart biopsies of individuals with cardiovascular risk factors. No biopsy studies have yet been performed on capillary rarefaction in individuals with early CKD. At present it is unknown whether individuals with CKD and cardiovascular disease merely share the same risk factors for capillary rarefaction, or whether there is a causal relationship between rarefaction in renal and systemic capillaries. Further studies on renal and systemic capillary rarefaction, including their temporal relationship and underlying mechanisms are needed. This review stresses the importance of preserving and maintaining capillary integrity and homeostasis in the prevention and management of renal and cardiovascular disease.

Is it time for Heart-Brain clinics? A clinical survey and proposition to improve current care for cognitive problems in heart failure

BACKGROUND

Cognitive impairment is highly prevalent among patients with heart failure (HF). International guidelines on the management of HF recommend screening for cognitive impairment and tailored care for patients with cognitive impairment. However, practical guidance is lacking. In this study, we explore cardiologists' perspective on screening and care for cognitive impairment in patients with HF. We give an example of a multidisciplinary Heart-Brain care pathway that facilitates screening for cognitive impairment in patients with HF.

METHODS

We distributed an online survey to cardiologists from the Dutch working groups on Geriatric Cardiology and Heart Failure. It covered questions about current clinical practice, impact of cognitive impairment on clinical decision-making, and their knowledge and skills to recognize cognitive impairment.

RESULTS

Thirty-six out of 55 invited cardiologists responded. Only 3% performed structured cognitive screening, while 83% stated that not enough attention is paid to cognitive impairment. More than half of the cardiologists desired more training in recognizing cognitive impairment and three-quarters indicated that knowing about cognitive impairment would change their treatment plan. Eighty percent agreed that systematic cognitive screening would benefit their patients and 74% wished to implement a Heart-Brain clinic. Time and expertise were addressed as the major barriers to screening for cognitive impairment.

CONCLUSION

Although cardiologists are aware of the clinical relevance of screening for cognitive impairment in cardiology patients, such clinical conduct is not yet commonly practiced due to lack of time and expertise. The Heart-Brain care pathway could facilitate this screening, thus improving personalized care in cardiology.

Cardiac output, cerebral blood flow and cognition in patients with severe aortic valve stenosis undergoing transcatheter aortic valve implantation: design and rationale of the CAPITA study

BACKGROUND

Approximately one-third of patients with symptomatic severe aortic valve stenosis who are scheduled for transcatheter aortic valve implantation (TAVI) have some degree of cognitive impairment. TAVI may have negative cognitive effects due to periprocedural micro-emboli inducing cerebral infarction. On the contrary, TAVI may also have positive cognitive effects due to increases in cardiac output and cerebral blood flow (CBF). However, studies that systematically assess these effects are scarce. Therefore, the main aim of this study is to assess cerebral and cognitive outcomes in patients with severe aortic valve stenosis undergoing TAVI.

STUDY DESIGN

In the prospective CAPITA (CArdiac OutPut, Cerebral Blood Flow and Cognition In Patients With Severe Aortic Valve Stenosis Undergoing Transcatheter Aortic Valve Implantation) study, cerebral and cognitive outcomes are assessed in patients undergoing TAVI. One day before and 3 months after TAVI, patients will undergo echocardiography (cardiac output, valve function), brain magnetic resonance imaging (CBF, structural lesions) and extensive neuropsychological assessment. To assess longer-term effects of TAVI, patients will again undergo echocardiography and neuropsychological assessment 1 year after the procedure. The co-primary outcome measures are change in CBF (in ml/100 g per min) and change in global cognitive functioning (Z-score) between baseline and 3‑month follow-up. Secondary objectives include change in cardiac output, white matter hyperintensities and other structural brain lesions. (ClinicalTrials.gov identifier NCT05481008) CONCLUSION : The CAPITA study is the first study designed to systematically assess positive and negative cerebral and cognitive outcomes after TAVI. We hypothesise that TAVI improves cardiac output, CBF and cognitive functioning.

Identification of CD8+ T cell PRDM1 in high-risk human plaques and its regulatory role in murine lesion development

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Fritz Thyssen Stiftung

T cells have a prominent role in the pathogenesis of atherosclerosis, although their function in atherosclerotic plaques is only partly understood. In this study, we utilize the advantages of high-throughput techniques and data analytic strategies to compare the inherent biological changes of T cells during plaque transition from a stable, non-haemorrhaged (low-risk) to a rupture-prone, haemorrhaged (high-risk) phenotype.

We classified 43 human carotid arterial lesions into high- and low-risk plaques based on the presence/absence of intraplaque hemorrhages. RNA from these lesions was isolated and microarray gene expression data was obtained and analyzed by Weighted Gene Co-expression Network Analysis. A strong T cell signalling signature was identified in high- versus low-risk plaques, influencing angiogenesis and interferon-related processes. Bayesian network inference, cell type deconvolution and single-cell RNA sequencing analysis revealed that the T cell-associated gene program was linked to effector-memory cytotoxic, CD8+ T cells. This gene program appeared driven by CD8+ T cell-related transcription factors, including RUNX3, IRF7 and most importantly PRDM1. To validate these findings, we demonstrated in a murine model that T cell PRDM1 plays a key role in plaque formation, as atherosclerotic mice with a T cell specific Prdm1 deficiency developed larger and more advanced atherosclerotic plaques compared to control mice.

In conclusion, our study unveils a clear PRDM1-regulated effector-memory cytotoxic CD8+ T cell footprint in plaque development and the shift from low- to high-risk plaques, thereby revealing CD8+ T cells and PRMD1 as potential targets for intervention in adverse T cell responses in human atherosclerotic lesions.

Noncanonical inhibition of caspase-3 by a nuclear microRNA confers endothelial protection by autophagy in atherosclerosis

MicroRNAs (miRNAs) are versatile regulators of gene expression with profound implications for human disease including atherosclerosis, but whether they can exert posttranslational functions to control cell adaptation and whether such noncanonical features harbor pathophysiological relevance is unknown. Here, we show that miR-126-5p sustains endothelial integrity in the context of high shear stress and autophagy. Bound to argonaute-2 (Ago2), miR-126-5p forms a complex with Mex3a, which occurs on the surface of autophagic vesicles and guides its transport into the nucleus. Mutational studies and biophysical measurements demonstrate that Mex3a binds to the central U- and G-rich regions of miR-126-5p with nanomolar affinity via its two K homology domains. In the nucleus, miR-126-5p dissociates from Ago2 and binds to caspase-3 in an aptamer-like fashion with its seed sequence, preventing dimerization of the caspase and inhibiting its activity to limit apoptosis. The antiapoptotic effect of miR-126-5p outside of the RNA-induced silencing complex is important for endothelial integrity under conditions of high shear stress promoting autophagy: ablation of Mex3a or ATG5 in vivo attenuates nuclear import of miR-126-5p, aggravates endothelial apoptosis, and exacerbates atherosclerosis. In human plaques, we found reduced nuclear miR-126-5p and active caspase-3 in areas of disturbed flow. The direct inhibition of caspase-3 by nuclear miR-126-5p reveals a noncanonical mechanism by which miRNAs can modulate protein function.

Integrative multiomics analysis of human atherosclerosis reveals a serum response factor-driven network associated with intraplaque hemorrhage

BACKGROUND

While single-omics analyses on human atherosclerotic plaque have been very useful to map stage- or disease-related differences in expression, they only partly capture the array of changes in this tissue and suffer from scale-intrinsic limitations. In order to better identify processes associated with intraplaque hemorrhage and plaque instability, we therefore combined multiple omics into an integrated model.

METHODS

In this study, we compared protein and gene makeup of low- versus high-risk atherosclerotic lesion segments from carotid endarterectomy patients, as judged from the absence or presence of intraplaque hemorrhage, respectively. Transcriptomic, proteomic, and peptidomic data of this plaque cohort were aggregated and analyzed by DIABLO, an integrative multivariate classification and feature selection method.

RESULTS

We identified a protein-gene associated multiomics model able to segregate stable, nonhemorrhaged from vulnerable, hemorrhaged lesions at high predictive performance (AUC >0.95). The dominant component of this model correlated with αSMA- PDGFRα+ fibroblast-like cell content (p = 2.4E-05) and Arg1+ macrophage content (p = 2.2E-04) and was driven by serum response factor (SRF), possibly in a megakaryoblastic leukemia-1/2 (MKL1/2) dependent manner. Gene set overrepresentation analysis on the selected key features of this model pointed to a clear cardiovascular disease signature, with overrepresentation of extracellular matrix synthesis and organization, focal adhesion, and cholesterol metabolism terms, suggestive of the model's relevance for the plaque vulnerability. Finally, we were able to corroborate the predictive power of the selected features in several independent mRNA and proteomic plaque cohorts.

CONCLUSIONS

In conclusion, our integrative omics study has identified an intraplaque hemorrhage-associated cardiovascular signature that provides excellent stratification of low- from high-risk carotid artery plaques in several independent cohorts. Further study revealed suppression of an SRF-regulated disease network, controlling lesion stability, in vulnerable plaque, which can serve as a scaffold for the design of targeted intervention in plaque destabilization.

Vascular Hypothesis of Alzheimer Disease: Topical Review of Mouse Models

[Figure: see text].

Iron Oxide Nanoparticle Uptake in Mouse Brachiocephalic Artery Atherosclerotic Plaque Quantified by T2-Mapping MRI

The purpose of our study was to monitor the iron oxide contrast agent uptake in mouse brachiocephalic artery (BCA) atherosclerotic plaques in vivo by quantitative T₂-mapping magnetic resonance imaging (MRI). Female ApoE^−/− mice (n = 32) on a 15-week Western-type diet developed advanced plaques in the BCA and were injected with ultra-small superparamagnetic iron oxides (USPIOs). Quantitative in vivo MRI at 9.4 T was performed with a Malcolm-Levitt (MLEV) prepared T₂-mapping sequence to monitor the nanoparticle uptake in the atherosclerotic plaque. Ex vivo histology and particle electron paramagnetic resonance (pEPR) were used for validation. Longitudinal high-resolution in vivo T₂-value maps were acquired with consistent quality. Average T₂ values in the plaque decreased from a baseline value of 34.5 ± 0.6 ms to 24.0 ± 0.4 ms one day after injection and partially recovered to an average T₂ of 27 ± 0.5 ms after two days. T₂ values were inversely related to iron levels in the plaque as determined by ex vivo particle electron paramagnetic resonance (pEPR). We concluded that MRI T₂ mapping facilitates a robust quantitative readout for USPIO uptake in atherosclerotic plaques in arteries near the mouse heart.

Arterial Remodeling of the Intracranial Arteries in Patients With Hypertension and Controls: A Postmortem Study

The intracranial arteries play a major role in cerebrovascular disease, but arterial remodeling due to hypertension has not been well described in humans. We aimed to quantify this remodeling for: the basilar artery, the vertebral, internal carotid, middle/anterior (inferior)/posterior cerebral, posterior communicating, and superior cerebellar arteries of the circle of Willis. Ex vivo circle of Willis specimens, selected from individuals with (n=24) and without (n=25) a history of hypertension, were imaged at 7T magnetic resonance imaging using a 3-dimensional gradient-echo sequence. Subsequently, histological analysis was performed. We validated the vessel wall thickness and area measurements from magnetic resonance imaging against histology. Next, we investigated potential differences in vessel wall thickness and area between both groups using both techniques. Finally, using histological analysis, we investigated potential differences in arterial wall stiffness and atherosclerotic plaque severity and load. All analyses were unadjusted. Magnetic resonance imaging and histology showed comparable vessel wall thickness (mean difference: 0.04 mm (limits of agreement:-0.12 to 0.19 mm) and area (0.43 mm² [-0.97 to 1.8 mm²]) measurements. We observed no statistically significant differences in vessel wall thickness and area between both groups using either technique. Histological analysis showed early and advanced atherosclerotic plaques in almost all arteries for both groups. The arterial wall stiffness was significantly higher for the internal carotid artery in the hypertensive group. Concluding, we did not observe vessel wall thickening in the circle of Willis arteries in individuals with a history of hypertension using either technique. Using histological analysis, we observed a difference in vessel wall composition for the internal carotid artery.

Inhibition of PFKFB3 Hampers the Progression of Atherosclerosis and Promotes Plaque Stability

Aims

6-phosphofructo-2-kinase/fructose-2,6-biphosphatase (PFKFB)3-mediated glycolysis is pivotal in driving macrophage- and endothelial cell activation and thereby inflammation. Once activated, these cells play a crucial role in the progression of atherosclerosis. Here, we analyzed the expression of PFKFB3 in human atherosclerotic lesions and investigated the therapeutic potential of pharmacological inhibition of PFKFB3 in experimental atherosclerosis by using the glycolytic inhibitor PFK158.

Methods and Results

PFKFB3 expression was higher in vulnerable human atheromatous carotid plaques when compared to stable fibrous plaques and predominantly expressed in plaque macrophages and endothelial cells. Analysis of advanced plaques of human coronary arteries revealed a positive correlation of PFKFB3 expression with necrotic core area. To further investigate the role of PFKFB3 in atherosclerotic disease progression, we treated 6-8 weeks old male Ldlr ^-/- mice. These mice were fed a high cholesterol diet for 13 weeks, of which they were treated for 5 weeks with the glycolytic inhibitor PFK158 to block PFKFB3 activity. The incidence of fibrous cap atheroma (advanced plaques) was reduced in PFK158-treated mice. Plaque phenotype altered markedly as both necrotic core area and intraplaque apoptosis decreased. This coincided with thickening of the fibrous cap and increased plaque stability after PFK158 treatment. Concomitantly, we observed a decrease in glycolysis in peripheral blood mononuclear cells compared to the untreated group, which alludes that changes in the intracellular metabolism of monocyte and macrophages is advantageous for plaque stabilization.

Conclusion

High PFKFB3 expression is associated with vulnerable atheromatous human carotid and coronary plaques. In mice, high PFKFB3 expression is also associated with a vulnerable plaque phenotype, whereas inhibition of PFKFB3 activity leads to plaque stabilization. This data implies that inhibition of inducible glycolysis may reduce inflammation, which has the ability to subsequently attenuate atherogenesis.

Cerebral Blood Flow in Patients with Severe Aortic Valve Stenosis Undergoing Transcatheter Aortic Valve Implantation

BACKGROUND

Transcatheter aortic valve implantation (TAVI) is a minimally invasive, life‐saving treatment for patients with severe aortic valve stenosis that improves quality of life. We examined cardiac output and cerebral blood flow in patients undergoing TAVI to test the hypothesis that improved cardiac output after TAVI is associated with an increase in cerebral blood flow.

DESIGN

Prospective cohort study.

SETTING

European high‐volume tertiary multidisciplinary cardiac care.

PARTICIPANTS

Thirty‐one patients (78.3 ± 4.6 years; 61% female) with severe symptomatic aortic valve stenosis.

MEASUREMENTS

Noninvasive prospective assessment of cardiac output (L/min) by inert gas rebreathing and cerebral blood flow of the total gray matter (mL/100 g per min) using arterial spin labeling magnetic resonance imaging in resting state less than 24 hours before TAVI and at 3‐month follow‐up. Cerebral blood flow change was defined as the difference relative to baseline.

RESULTS

On average, cardiac output in patients with severe aortic valve stenosis increased from 4.0 ± 1.1 to 5.4 ± 2.4 L/min after TAVI (P = .003). The increase in cerebral blood flow after TAVI strongly varied between patients (7% ± 24%; P = .41) and related to the increase in cardiac output, with an 8.2% (standard error = 2.3%; P = .003) increase in cerebral blood flow per every additional liter of cardiac output following the TAVI procedure.

CONCLUSION

Following TAVI, there was an association of increase in cardiac output with increase in cerebral blood flow. These findings encourage future larger studies to determine the influence of TAVI on cerebral blood flow and cognitive function.

Autophagy unleashes noncanonical microRNA functions

MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression which act by guiding AGO (argonaute) proteins to target RNA transcripts in the RNA-induced silencing complex (RISC). This macromolecular complex includes multiple additional components (e.g., TNRC6A) that allow for interaction with enzymes mediating inhibition of translation or RNA decay. However, miRNAs also reside in low-molecular weight complexes without being engaged in target repression, and their function in this context is largely unknown. Our recent findings show that endothelial cells exposed to protective high-shear stress or MTORC inhibition activate the macroautophagy/autophagy machinery to sustain viability by promoting differential trafficking of MIR126 strands and by enabling unconventional features of MIR126-5p. Whereas MIR126-3p is degraded upon autophagy activation, MIR126-5p interacts with the RNA-binding protein MEX3A to form a ternary complex with AGO2. This complex forms on the autophagosomal surface and facilitates its nuclear localization. Once in the nucleus, MIR126-5p dissociates from AGO2 and establishes aptamer-like interactions with the effector CASP3 (caspase 3). The binding to MIR126-5p prevents dimerization and proper active site formation of CASP3, thus inhibiting proteolytic activity and limiting apoptosis. Disrupting this pathway in vivo by genetic deletion of Mex3a or by specific deficiency of endothelial autophagy aggravates endothelial apoptosis and exacerbates the progression of atherosclerosis. The direct inhibition of CASP3 by MIR126-5p reveals a non-canonical mechanism by which miRNAs can modulate protein function and mediate the autophagy-apoptosis crosstalk.

Deficiency of the T cell regulator Casitas B-cell lymphoma-B aggravates atherosclerosis by inducing CD8+ T cell-mediated macrophage death

Aims

The E3-ligase CBL-B (Casitas B-cell lymphoma-B) is an important negative regulator of T cell activation that is also expressed in macrophages. T cells and macrophages mediate atherosclerosis, but their regulation in this disease remains largely unknown; thus, we studied the function of CBL-B in atherogenesis.

Methods and results

The expression of CBL-B in human atherosclerotic plaques was lower in advanced lesions compared with initial lesions and correlated inversely with necrotic core area. Twenty weeks old Cblb^−/−Apoe^−/− mice showed a significant increase in plaque area in the aortic arch, where initial plaques were present. In the aortic root, a site containing advanced plaques, lesion area rose by 40%, accompanied by a dramatic change in plaque phenotype. Plaques contained fewer macrophages due to increased apoptosis, larger necrotic cores, and more CD8⁺ T cells. Cblb^−/−Apoe^−/− macrophages exhibited enhanced migration and increased cytokine production and lipid uptake. Casitas B-cell lymphoma-B deficiency increased CD8⁺ T cell numbers, which were protected against apoptosis and regulatory T cell-mediated suppression. IFNγ and granzyme B production was enhanced in Cblb^−/−Apoe^−/− CD8⁺ T cells, which provoked macrophage killing. Depletion of CD8⁺ T cells in Cblb^−/−Apoe^−/− bone marrow chimeras rescued the phenotype, indicating that CBL-B controls atherosclerosis mainly through its function in CD8⁺ T cells.

Conclusion

Casitas B-cell lymphoma-B expression in human plaques decreases during the progression of atherosclerosis. As an important regulator of immune responses in experimental atherosclerosis, CBL-B hampers macrophage recruitment and activation during initial atherosclerosis and limits CD8⁺ T cell activation and CD8⁺ T cell-mediated macrophage death in advanced atherosclerosis, thereby preventing the progression towards high-risk plaques.

Profiling the unique protective properties of intracranial arterial endothelial cells

Cardiovascular disorders, like atherosclerosis and hypertension, are increasingly known to be associated with vascular cognitive impairment (VCI). In particular, intracranial atherosclerosis is one of the main causes of VCI, although plaque development occurs later in time and is structurally different compared to atherosclerosis in extracranial arteries. Recent data suggest that endothelial cells (ECs) that line the intracranial arteries may exert anti-atherosclerotic effects due to yet unidentified pathways. To gain insights into underlying mechanisms, we isolated post-mortem endothelial cells from both the intracranial basilar artery (BA) and the extracranial common carotid artery (CCA) from the same individual (total of 15 individuals) with laser capture microdissection. RNA sequencing revealed a distinct molecular signature of the two endothelial cell populations of which the most prominent ones were validated by means of qPCR. Our data reveal for the first time that intracranial artery ECs exert an immune quiescent phenotype. Secondly, genes known to be involved in the response of ECs to damage (inflammation, differentiation, adhesion, proliferation, permeability and oxidative stress) are differentially expressed in intracranial ECs compared to extracranial ECs. Finally, Desmoplakin (DSP) and Hop Homeobox (HOPX), two genes expressed at a higher level in intracranial ECs, and Sodium Voltage-Gated Channel Beta Subunit 3 (SCN3B), a gene expressed at a lower level in intracranial ECs compared to extracranial ECs, were shown to be responsive to shear stress and/or hypoxia. With our data we present a set of intracranial-specific endothelial genes that may contribute to its protective phenotype, thereby supporting proper perfusion and consequently may preserve cognitive function. Deciphering the molecular regulation of the vascular bed in the brain may lead to the identification of novel potential intervention strategies to halt vascular associated disorders, such as atherosclerosis and vascular cognitive dysfunction.

Microvasculature and intraplaque hemorrhage in atherosclerotic carotid lesions: a cardiovascular magnetic resonance imaging study

BACKGROUND

The presence of intraplaque haemorrhage (IPH) has been related to plaque rupture, is associated with plaque progression, and predicts cerebrovascular events. However, the mechanisms leading to IPH are not fully understood. The dominant view is that IPH is caused by leakage of erythrocytes from immature microvessels. The aim of the present study was to investigate whether there is an association between atherosclerotic plaque microvasculature and presence of IPH in a relatively large prospective cohort study of patients with symptomatic carotid plaque.

METHODS

One hundred and thirty-two symptomatic patients with ≥2 mm carotid plaque underwent cardiovascular magnetic resonance (CMR) of the symptomatic carotid plaque for detection of IPH and dynamic contrast-enhanced (DCE)-CMR for assessment of plaque microvasculature. Ktrans, an indicator of microvascular flow, density and leakiness, was estimated using pharmacokinetic modelling in the vessel wall and adventitia. Statistical analysis was performed using an independent samples T-test and binary logistic regression, correcting for clinical risk factors.

RESULTS

A decreased vessel wall Ktrans was found for IPH positive patients (0.051 ± 0.011 min- 1 versus 0.058 ± 0.017 min- 1, p = 0.001). No significant difference in adventitial Ktrans was found in patients with and without IPH (0.057 ± 0.012 min- 1 and 0.057 ± 0.018 min- 1, respectively). Histological analysis in a subgroup of patients that underwent carotid endarterectomy demonstrated no significant difference in relative microvessel density between plaques without IPH (n = 8) and plaques with IPH (n = 15) (0.000333 ± 0.0000707 vs. and 0.000289 ± 0.0000439, p = 0.585).

CONCLUSIONS

A reduced vessel wall Ktrans is found in the presence of IPH. Thus, we did not find a positive association between plaque microvasculature and IPH several weeks after a cerebrovascular event. Not only leaky plaque microvessels, but additional factors may contribute to IPH development.

TRIAL REGISTRATION

NCT01208025 . Registration date September 23, 2010. Retrospectively registered (first inclusion September 21, 2010). NCT01709045 , date of registration October 17, 2012. Retrospectively registered (first inclusion August 23, 2011).

Aging modifies the effect of cardiac output on middle cerebral artery blood flow velocity

An association between cerebral blood flow (CBF) and cardiac output (CO) has been established in young healthy subjects. As of yet it is unclear how this association evolves over the life span. To that purpose, we continuously recorded mean arterial pressure (MAP; finger plethysmography), CO (pulse contour; CO‐trek), mean blood flow velocity in the middle cerebral artery (MCAV; transcranial Doppler ultrasonography), and end‐tidal CO₂ partial pressure (PetCO₂) in healthy young (19–27 years), middle‐aged (51–61 years), and elderly subjects (70–79 years). Decreases and increases in CO were accomplished using lower body negative pressure and dynamic handgrip exercise, respectively. Aging in itself did not alter dynamic cerebral autoregulation or cerebrovascular CO₂ reactivity. A linear relation between changes in CO and MCAV_mean was observed in middle‐aged (P < 0.01) and elderly (P = 0.04) subjects but not in young (P = 0.45) subjects, taking concurrent changes in MAP and PetCO₂ into account. These data imply that with aging, brain perfusion becomes increasingly dependent on CO.

The Missing Link in the Pathophysiology of Vascular Cognitive Impairment: Design of the Heart-Brain Study

Background

Hemodynamic balance in the heart-brain axis is increasingly recognized as a crucial factor in maintaining functional and structural integrity of the brain and thereby cognitive functioning. Patients with heart failure (HF), carotid occlusive disease (COD), and vascular cognitive impairment (VCI) present themselves with complaints attributed to specific parts of the heart-brain axis, but hemodynamic changes often go beyond the part of the axis for which they primarily seek medical advice. The Heart-Brain Study hypothesizes that the hemodynamic status of the heart and the brain is an important but underestimated cause of VCI. We investigate this by studying to what extent hemodynamic changes contribute to VCI and what the mechanisms involved are. Here, we provide an overview of the design and protocol.

Methods

The Heart-Brain Study is a multicenter cohort study with a follow-up measurement after 2 years among 645 participants (175 VCI, 175 COD, 175 HF, and 120 controls). Enrollment criteria are the following: 1 of the 3 diseases diagnosed according to current guidelines, age ≥50 years, no magnetic resonance contraindications, ability to undergo cognitive testing, and independence in daily life. A core clinical dataset is collected including sociodemographic factors, cardiovascular risk factors, detailed neurologic, cardiac, and medical history, medication, and a physical examination. In addition, we perform standardized neuropsychological testing, cardiac, vascular and brain MRI, and blood sampling. In subsets of participants we assess Alz­heimer biomarkers in cerebrospinal fluid, and assess echocardiography and 24-hour blood pressure monitoring. Follow-up measurements after 2 years include neuropsychological testing, brain MRI, and blood samples for all participants. We use centralized state-of-the-art storage platforms for clinical and imaging data. Imaging data are processed centrally with automated standardized pipelines.

Results and Conclusions

The Heart-Brain Study investigates relationships between (cardio-)vascular factors, the hemodynamic status of the heart and the brain, and cognitive impairment. By studying the complete heart-brain axis in patient groups that represent components of this axis, we have the opportunity to assess a combination of clinical and subclinical manifestations of disorders of the heart, vascular system and brain, with hemodynamic status as a possible binding factor.

Recommendation on Design, Execution, and Reporting of Animal Atherosclerosis Studies: A Scientific Statement From the American Heart Association

Animal studies are a foundation for defining mechanisms of atherosclerosis and potential targets of drugs to prevent lesion development or reverse the disease. In the current literature, it is common to see contradictions of outcomes in animal studies from different research groups, leading to the paucity of extrapolations of experimental findings into understanding the human disease. The purpose of this statement is to provide guidelines for development and execution of experimental design and interpretation in animal studies. Recommendations include the following: (1) animal model selection, with commentary on the fidelity of mimicking facets of the human disease; (2) experimental design and its impact on the interpretation of data; and (3) standard methods to enhance accuracy of measurements and characterization of atherosclerotic lesions.

Intraleaflet hemorrhages are a common finding in symptomatic aortic and mitral valves

INTRODUCTION

Intraleaflet hemorrhage (ILH) has been reported to occur in calcified degenerated aortic valves. At present, no such information is available for mitral valves or for other types of valvular disease. We examined the prevalence, age, and potential source of ILH in a consecutive series of surgically removed aortic and mitral valves, and related the findings to specific types of heart valve pathology.

METHODS

A total of 105 aortic (n=85) and mitral (n=20) valves were retrieved from 100 symptomatic patients. Pathological diagnosis was made on photographic images and histology. Presence, extent, and age of ILH; its possible association with calcification; microvessels; and microvascular leakage were assessed with conventional and immunohistochemical staining methods and related to the type of underlying valvular disease.

RESULTS

Pathological diagnosis revealed degenerative aortic valve disease (n=70), postinflammatory disease (n=16), endocarditis (n=12), myxoid degenerative mitral valve disease (n=6), and one normal valve. ILH was found in 86% of aortic and 75% of mitral valves. Microvessels were present in 91% of all valves. Microvascular leakage was noted in 70% of aortic and 84% of mitral valves; in both groups, colocalization with ILH was found in 48%. Most aortic valves (91%) contained calcium deposits, of which 54% showed colocalization with ILH. In 66% of valves with ILH, a combination of recent hemorrhage and iron deposits was seen, indicating an ongoing process of episodic hemorrhages.

CONCLUSION

The prevalence of ILH is very high in resected heart valves. Both aortic and mitral valves showed an association of ILH with microvessels, microvascular leakage, and calcifications. We speculate that repetitive microvascular-leakage-related ILH may contribute to valve dysfunction on the (very) long term.

Imaging Intraplaque Inflammation in Carotid Atherosclerosis With 18F-Fluorocholine Positron Emission Tomography-Computed Tomography: Prospective Study on Vulnerable Atheroma With Immunohistochemical Validation

BACKGROUND

(18)F-fluorocholine ((18)F-FCH) uptake is associated with cell proliferation and activity in tumor patients. We hypothesized that (18)F-FCH could similarly be a valuable imaging tool to identify vulnerable plaques and associated intraplaque inflammation and atheroma cell proliferation.

METHODS AND RESULTS

Ten consecutive stroke patients (90% men, median age 66.5 years, range, 59.4-69.7) with ipsilateral >70% carotid artery stenosis and who underwent carotid endarterectomy were included in the study. Before carotid endarterectomy, all patients underwent positron emission tomography to assess maximum (18)F-FCH uptake in ipsilateral symptomatic carotid plaques and contralateral asymptomatic carotid arteries, which was corrected for background activity, resulting in a maximum target-to-background ratio (TBRmax). Macrophage content was assessed in all carotid endarterectomy specimens as a percentage of CD68(+)-staining per whole plaque area (plaqueCD68(+)) and as a maximum CD68(+) percentage (maxCD68(+)) in the most inflamed section/plaque. Dynamic positron emission tomography imaging demonstrated that an interval of 10 minutes between (18)F-FCH injection and positron emission tomography acquisition is appropriate for carotid plaque imaging. TBRmax in ipsilateral symptomatic carotid plaques correlated significantly with plaqueCD68(+) (Spearman's ρ=0.648, P=0.043) and maxCD68(+) (ρ=0.721, P=0.019) in the 10 corresponding carotid endarterectomy specimens. TBRmax was significantly higher (P=0.047) in ipsilateral symptomatic carotid plaques (median: 2.0; interquartile range [Q1-Q3], 1.5-2.5) compared with the contralateral asymptomatic carotid arteries (median: 1.4; Q1-Q3, 1.3-1.6). TBRmax was not significantly correlated to carotid artery stenosis (ρ=0.506, P=0.135).

CONCLUSIONS

In vivo uptake of (18)F-FCH in human carotid atherosclerotic plaques correlated strongly with degree of macrophage infiltration and recent symptoms, thus (18)F-FCH positron emission tomography is a promising tool for the evaluation of vulnerable plaques.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01899014.

Abnormal haemodynamic postural response in patients with chronic heart failure

Aim

The objective was to evaluate in treated heart failure (HF) patients whether multidrug therapy interferes with the cardiovascular autonomic response to postural stress.

Methods and results

Blood pressure (BP; Finapres), heart rate (HR), stroke volume, and total peripheral resistance (TPR) responses to standing up were measured in 33 HF patients and 10 healthy age‐matched controls. Ten hypertensive (HT) patients treated with a similar combination of drugs but without heart failure served as reference subjects to account for use of medication. Frequency domain measures of HR and BP variability were calculated as correlates of cardiovascular autonomic function. Postural hypotension was found in 16 out of 33 HF patients independently from New York Heart Association functional class. In HF patients vs. HT patients and healthy controls the haemodynamic postural response was abnormal with a large initial BP fall and a slackened reflex increase in TPR resulting in inadequate BP recovery. HR and BP variability were normal in HT patients and healthy controls but attenuated in HF patients. The magnitude of the postural HR, stroke volume, and TPR responses as well as HR and BP variability was inversely related to the New York Heart Association class.

Conclusions

In HF patients, the autonomic vasomotor response to postural stress is abnormal, more pronounced with increasing disease severity, and frequently associated with overt postural hypotension. These phenomena appear related to the cardiac condition rather than treatment.

Vessel wall and adventitial DCE-MRI parameters demonstrate similar correlations with carotid plaque microvasculature on histology

PURPOSE

To assess parameter agreement of volume transfer coefficient (K^trans ) between two vascular regions and to study the correlation with microvessel density on histology. The dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) parameter K^trans is frequently used to study atherosclerotic plaque microvasculature. K^trans has been reported using different descriptive statistics (mean, median, 75^th percentile) either for the whole vessel wall or the adventitia in previous studies.

MATERIALS AND METHODS

DCE-MRI parameter agreement was analyzed in 110 symptomatic patients with ≥2 mm carotid plaque that underwent a 3T carotid DCE-MRI examination. K^trans was estimated in the entire vessel wall and adventitia. Twenty-three patients underwent carotid endarterectomy and were used for comparison with histological quantification of microvessel density of the plaque using CD31 immunohistochemistry. DCE-MRI parameters in the vessel wall regions were compared using Pearson's correlation coefficient, Bland-Altman analysis, and a two-sided paired samples t-test. Correlation of the DCE-MRI parameters with histology was studied using the Pearson's correlation coefficient.

RESULTS

Median adventitial K^trans was 5% higher (P = 0.003) than entire vessel wall K^trans , with no differences for other descriptive statistics. Vessel wall and adventitial K^trans showed similar moderately strong correlations with plaque microvessel density on histology (Pearson's ρ: 0.59-0.65 [P < 0.003] and 0.52-0.64 [P < 0.011], respectively).

CONCLUSION

The similar moderately strong correlations for vessel wall and adventitial K^trans with microvessel density on histology suggested that both regions reflected plaque microvessel density. Care should to be taken when comparing absolute values between studies. Future studies incorporating thresholds for risk stratification need to agree upon standardization of DCE-MRI parameters.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2017;46:1053-1059.

The cerebrovascular response to lower-body negative pressure vs. head-up tilt

Lower-body negative pressure (LBNP) has been proposed as a MRI-compatible surrogate for orthostatic stress. Although the effects of LBNP on cerebral hemodynamic behavior have been considered to reflect those of orthostatic stress, a direct comparison with actual orthostasis is lacking. We assessed the effects of LBNP (-50 mmHg) vs. head-up tilt (HUT; at 70°) in 10 healthy subjects (5 female) on transcranial Doppler-determined cerebral blood flow velocity (CBFv) in the middle cerebral artery and cerebral perfusion pressure (CPP) as estimated from the blood pressure signal (finger plethysmography). CPP was maintained during LBNP but decreased after 2 min in response to HUT, leading to an ~15% difference in CPP between LBNP and HUT (P ≤ 0.020). Mean CBFv initially decreased similarly in response to LBNP and for HUT, but, from minute 3 on, the decline became ~50% smaller (P ≤ 0.029) during LBNP. The reduction in end-tidal Pco₂ partial pressure (Pet_CO2 ) was comparable but with an earlier return toward baseline values in response to LBNP but not during HUT (P = 0.008). We consider the larger decrease in CBFv during HUT vs. LBNP attributable to the pronounced reduction in Pet_CO2 and to gravitational influences on CPP, and this should be taken into account when applying LBNP as an MRI-compatible orthostatic stress modality.NEW & NOTEWORTHY Lower-body negative pressure (LBNP) has the potential to serve as a MRI-compatible surrogate of orthostatic stress but a comparison with actual orthostasis was lacking. This study showed that the pronounced reduction in end-tidal Pco₂ together with gravitational effects on the brain circulation lead to a larger decline in cerebral blood flow velocity in response to head-up tilt than during lower-body negative pressure. This should be taken into account when employing lower-body negative pressure as MRI-compatible alternative to orthostatic stress.

MerTK receptor cleavage promotes plaque necrosis and defective resolution in atherosclerosis

Atherothrombotic vascular disease is often triggered by a distinct type of atherosclerotic lesion that displays features of impaired inflammation resolution, notably a necrotic core and thinning of a protective fibrous cap that overlies the core. A key cause of plaque necrosis is defective clearance of apoptotic cells, or efferocytosis, by lesional macrophages, but the mechanisms underlying defective efferocytosis and its possible links to impaired resolution in atherosclerosis are incompletely understood. Here, we provide evidence that proteolytic cleavage of the macrophage efferocytosis receptor c-Mer tyrosine kinase (MerTK) reduces efferocytosis and promotes plaque necrosis and defective resolution. In human carotid plaques, MerTK cleavage correlated with plaque necrosis and the presence of ischemic symptoms. Moreover, in fat-fed LDL receptor-deficient (Ldlr-/-) mice whose myeloid cells expressed a cleavage-resistant variant of MerTK, atherosclerotic lesions exhibited higher macrophage MerTK, lower levels of the cleavage product soluble Mer, improved efferocytosis, smaller necrotic cores, thicker fibrous caps, and increased ratio of proresolving versus proinflammatory lipid mediators. These findings provide a plausible molecular-cellular mechanism that contributes to defective efferocytosis, plaque necrosis, and impaired resolution during the progression of atherosclerosis.

Live Observation of Atherosclerotic Plaque Disruption in Apolipoprotein E-Deficient Mouse

AIM

The actual occurrence of spontaneous plaque rupture in mice has been a matter of debate. We report on an in vivo observation of the actual event of possible plaque disruption in a living ApoE(-/-) mouse.

METHODS AND RESULTS

During live contrast-enhanced ultrasonography of a 50-week-old ApoE(-/-) male mouse, symptoms suggesting plaque disruption in the brachiocephalic artery were observed. Histological analysis confirmed the presence of advanced atherosclerotic lesions with dissections and intraplaque hemorrhage in the affected brachiocephalic trunk, pointing towards plaque rupture as the cause of the observed event. However, we did not detect a luminal thrombus or cap rupture, which is a key criterion for plaque rupture in human atherosclerosis.

CONCLUSION

This study reports the real-time occurrence of a possible plaque rupture in a living ApoE(-/-) mouse.

Quantification of Endothelial αvβ3 Expression with High-Frequency Ultrasound and Targeted Microbubbles: In Vitro and In Vivo Studies

Angiogenesis is a critical feature of plaque development in atherosclerosis and might play a key role in both the initiation and later rupture of plaques. The precursory molecular or cellular pro-angiogenic events that initiate plaque growth and that ultimately contribute to plaque instability, however, cannot be detected directly with any current diagnostic modality. This study was designed to investigate the feasibility of ultrasound molecular imaging of endothelial αvβ3 expression in vitro and in vivo using αvβ3-targeted ultrasound contrast agents (UCAs). In the in vitro study, αvβ3 expression was confirmed by immunofluorescence in a murine endothelial cell line and detected using the targeted UCA and ultrasound imaging at 18-MHz transmit frequency. In the in vivo study, expression of endothelial αvβ3 integrin in murine carotid artery vessels and microvessels of the salivary gland was quantified using targeted UCA and high-frequency ultrasound in seven animals. Our results indicated that endothelial αvβ3 expression was significantly higher in the carotid arterial wall containing atherosclerotic lesions than in arterial segments without any lesions. We also found that the salivary gland can be used as an internal positive control for successful binding of targeted UCA to αvβ3 integrin. In conclusion, αvβ3-targeted UCA allows non-invasive assessment of the expression levels of αvβ3 on the vascular endothelium and may provide potential insights into early atherosclerotic plaque detection and treatment monitoring.

Intracranial Vessel Wall MRI: Principles and Expert Consensus Recommendations of the American Society of Neuroradiology

Intracranial vessel wall MR imaging is an adjunct to conventional angiographic imaging with CTA, MRA, or DSA. The technique has multiple potential uses in the context of ischemic stroke and intracranial hemorrhage. There remain gaps in our understanding of intracranial vessel wall MR imaging findings and research is ongoing, but the technique is already used on a clinical basis at many centers. This article, on behalf of the Vessel Wall Imaging Study Group of the American Society of Neuroradiology, provides expert consensus recommendations for current clinical practice.

Cardiovascular Response Patterns to Sympathetic Stimulation by Central Hypovolemia

In healthy subjects, variation in cardiovascular responses to sympathetic stimulation evoked by submaximal lower body negative pressure (LBNP) is considerable. This study addressed the question whether inter-subject variation in cardiovascular responses coincides with consistent and reproducible responses in an individual subject. In 10 healthy subjects (5 female, median age 22 years), continuous hemodynamic parameters (finger plethysmography; Nexfin, Edwards Lifesciences), and time-domain baroreflex sensitivity (BRS) were quantified during three consecutive 5-min runs of LBNP at −50 mmHg. The protocol was repeated after 1 week to establish intra-subject reproducibility. In response to LBNP, 5 subjects (3 females) showed a prominent increase in heart rate (HR; 54 ± 14%, p = 0.001) with no change in total peripheral resistance (TPR; p = 0.25) whereas the other 5 subjects (2 females) demonstrated a significant rise in TPR (7 ± 3%, p = 0.017) with a moderate increase in HR (21 ± 9%, p = 0.004). These different reflex responses coincided with differences in resting BRS (22 ± 8 vs. 11 ± 3 ms/mmHg, p = 0.049) and resting HR (57 ± 8 vs. 71 ± 12 bpm, p = 0.047) and were highly reproducible over time. In conclusion, we found distinct cardiovascular response patterns to sympathetic stimulation by LBNP in young healthy individuals. These patterns of preferential autonomic blood pressure control appeared related to resting cardiac BRS and HR and were consistent over time.

Atherosclerosis in the circle of Willis: Spatial differences in composition and in distribution of plaques

BACKGROUND AND AIMS

Intracranial atherosclerosis is one of the main causes of ischemic stroke. However, the characteristics of intracranial arteries and atherosclerosis have rarely been studied. Therefore, we systematically investigated atherosclerotic changes in all arteries of the Circle of Willis (CoW).

METHODS

Sixty-seven CoWs obtained at autopsy from randomly chosen hospital patients (mean age, 67.3 ± 12.5 years), of which a total of 1220 segments were collected from 22 sites. Atherosclerotic plaques were classified according to the revised American Heart Association classification and were related to local vessel characteristics, such as the presence of an external and internal elastic lamina and the elastic fibre density of the media.

RESULTS

181 out of the 1220 segments had advanced plaques (15%), which were mainly observed in large arteries such as the internal carotid, middle cerebral, basilar and vertebral artery. Only 11 out of 1220 segments (1%) showed complicated plaques (p < 0.001). Six of these were intraplaque hemorrhages (IPH) and observed only in patients who had cardiovascular-related events (p = 0.015). The frequency of characteristics such as the external elastic lamina and a high elastin fibre density in the media was most often associated with the vertebral artery. Only 3% (n = 33) of the CoW arteries contained calcification (p < 0.001), which were mostly observed in the vertebral artery (n = 13, 12%).

CONCLUSIONS

Advanced atherosclerotic plaques in the CoW are relatively scarce and mainly located in the 4 large arteries, and mostly characterized by an early and stable phenotype, a low calcific burden, and a low frequency of IPH.

Phase-based vascular input function: Improved quantitative DCE-MRI of atherosclerotic plaques

PURPOSE

Quantitative pharmacokinetic modeling of dynamic contrast-enhanced (DCE)-MRI can be used to assess atherosclerotic plaque microvasculature, which is an important marker of plaque vulnerability. Purpose of the present study was (1) to compare magnitude- versus phase-based vascular input functions (m-VIF vs ph-VIF) used in pharmacokinetic modeling and (2) to perform model calculations and flow phantom experiments to gain more insight into the differences between m-VIF and ph-VIF.

METHODS

Population averaged m-VIF and ph-VIFs were acquired from 11 patients with carotid plaques and used for pharmacokinetic analysis in another 17 patients. Simulations, using the Bloch equations and the MRI scan geometry, and flow phantom experiments were performed to determine the effect of local blood velocity on the magnitude and phase signal enhancement.

RESULTS

Simulations and flow phantom experiments revealed that flow within the lumen can lead to severe underestimation of m-VIF, while this is not the case for the ph-VIF. In line, the peak concentration of the m-VIF is significantly lower than ph-VIF (p < 0.001), in vivo. Quantitative model parameters for m- and ph-VIF differed in absolute values but were moderate to strongly correlated with each other [K(trans) Spearman's ρ > 0.93 (p < 0.001) and vp Spearman's ρ > 0.58 (p < 0.05)].

CONCLUSIONS

m-VIF is strongly influenced by local blood velocity, which leads to underestimation of the contrast medium concentration. Therefore, it is advised to use ph-VIF for DCE-MRI analysis of carotid plaques for accurate quantification.

Deficiency of the oxygen sensor prolyl hydroxylase 1 attenuates hypercholesterolaemia, atherosclerosis, and hyperglycaemia

AIMS

Normalization of hypercholesterolaemia, inflammation, hyperglycaemia, and obesity are main desired targets to prevent cardiovascular clinical events. Here we present a novel regulator of cholesterol metabolism, which simultaneously impacts on glucose intolerance and inflammation.

METHODS AND RESULTS

Mice deficient for oxygen sensor HIF-prolyl hydroxylase 1 (PHD1) were backcrossed onto an atherogenic low-density lipoprotein receptor (LDLR) knockout background and atherosclerosis was studied upon 8 weeks of western-type diet. PHD1^-/-LDLR^-/- mice presented a sharp reduction in VLDL and LDL plasma cholesterol levels. In line, atherosclerotic plaque development, as measured by plaque area, necrotic core expansion and plaque stage was hampered in PHD1^-/-LDLR^-/- mice. Mechanistically, cholesterol-lowering in PHD1 deficient mice was a result of enhanced cholesterol excretion from blood to intestines and ultimately faeces. Additionally, flow cytometry of whole blood of these mice revealed significantly reduced counts of leucocytes and particularly of Ly6C^high pro-inflammatory monocytes. In addition, when studying PHD1^-/- in diet-induced obesity (14 weeks high-fat diet) mice were less glucose intolerant when compared with WT littermate controls.

CONCLUSION

Overall, PHD1 knockout mice display a metabolic phenotype that generally is deemed protective for cardiovascular disease. Future studies should focus on the efficacy, safety, and gender-specific effects of PHD1 inhibition in humans, and unravel the molecular actors responsible for PHD1-driven, likely intestinal, and regulation of cholesterol metabolism.

The effect of prolonged dietary nitrate supplementation on atherosclerosis development

BACKGROUND

Short term dietary nitrate or nitrite supplementation has nitric oxide (NO)-mediated beneficial effects on blood pressure and inflammation and reduces mitochondrial oxygen consumption, possibly preventing hypoxia. As these processes are implicated in atherogenesis, dietary nitrate was hypothesized to prevent plaque initiation, hypoxia and inflammation.

AIMS

Study prolonged nitrate supplementation on atherogenesis, hypoxia and inflammation in low density lipoprotein receptor knockout mice (LDLr(-/-)).

METHODS

LDLr(-/-) mice were administered sodium-nitrate or equimolar sodium-chloride in drinking water alongside a western-type diet for 14 weeks to induce atherosclerosis. Plasma nitrate, nitrite and hemoglobin-bound nitric oxide were measured by chemiluminescence and electron parametric resonance, respectively.

RESULTS

Plasma nitrate levels were elevated after 14 weeks of nitrate supplementation (NaCl: 40.29 ± 2.985, NaNO3: 78.19 ± 6.837, p < 0.0001). However, prolonged dietary nitrate did not affect systemic inflammation, hematopoiesis, erythropoiesis and plasma cholesterol levels, suggesting no severe side effects. Surprisingly, neither blood pressure, nor atherogenesis were altered. Mechanistically, plasma nitrate and nitrite were elevated after two weeks (NaCl: 1.0 ± 0.2114, NaNO3: 3.977 ± 0.7371, p < 0.0001), but decreased over time (6, 10 and 14 weeks). Plasma nitrite levels even reached baseline levels at 14 weeks (NaCl: 0.7188 ± 0.1072, NaNO3: 0.9723 ± 0.1279 p = 0.12). Also hemoglobin-bound NO levels were unaltered after 14 weeks. This compensation was not due to altered eNOS activity or conversion into peroxynitrite and other RNI, suggesting reduced nitrite formation or enhanced nitrate/nitrite clearance.

CONCLUSION

Prolonged dietary nitrate supplementation resulted in compensation of nitrite and NO levels and did not affect atherogenesis or exert systemic side effects.

Neovascularization of the atherosclerotic plaque: interplay between atherosclerotic lesion, adventitia-derived microvessels and perivascular fat

PURPOSE OF REVIEW

Neovascularization is a prominent feature in advanced human atherosclerotic plaques. This review surveys recent evidence for and remaining uncertainties regarding a role of neovascularization in atherosclerotic plaque progression. Specific emphasis is given to hypoxia, angiogenesis inhibition, and perivascular adipose tissue (PVAT).

RECENT FINDINGS

Immunohistochemical and imaging studies showed a strong association between hypoxia, inflammation and neovascularization, and the progression of the atherosclerotic plaque both in humans and mice. Whereas in humans, a profound invasion of microvessels from the adventitia into the plaque occurs, neovascularization in mice is found mainly (peri)adventitially. Influencing neovascularization in mice affected plaque progression, possibly by improving vessel perfusion, but supportive clinical data are not available. Whereas plaque neovascularization contributes to monocyte/macrophage accumulation in the plaque, lymphangiogenesis may facilitate egress of cells and waste products. A specific role for PVAT and its secreted factors is anticipated and wait further clinical evaluation.

SUMMARY

Hypoxia, inflammation, and plaque neovascularization are associated with plaque progression as underpinned by recent imaging data in humans. Recent studies provide new insights into modulation of adventitia-associated angiogenesis, PVAT, and plaque development in mice, but there is still a need for detailed information on modulating human plaque vascularization in patients.

Intraplaque Hemorrhage and the Plaque Surface in Carotid Atherosclerosis: The Plaque At RISK Study (PARISK)

BACKGROUND AND PURPOSE

An important characteristic of vulnerable plaque, intraplaque hemorrhage, may predict plaque rupture. Plaque rupture can be visible on noninvasive imaging as a disruption of the plaque surface. We investigated the association between intraplaque hemorrhage and disruption of the plaque surface.

MATERIALS AND METHODS

We selected the first 100 patients of the Plaque At RISK study, an ongoing prospective noninvasive plaque imaging study in patients with mild-to-moderate atherosclerotic lesions in the carotid artery. In carotid artery plaques, disruption of the plaque surface (defined as ulcerated plaques and/or fissured fibrous cap) and intraplaque hemorrhage were assessed by using MDCTA and 3T MR imaging, respectively. We used a χ(2) test and multivariable logistic regression to assess the association between intraplaque hemorrhage and disrupted plaque surface.

RESULTS

One hundred forty-nine carotid arteries in 78 patients could be used for the current analyses. Intraplaque hemorrhage and plaque ulcerations were more prevalent in symptomatic compared with contralateral vessels (hemorrhage, 38% versus 11%; P < .001; and ulcerations, 27% versus 7%; P = .001). Fissured fibrous cap was more prevalent in symptomatic compared with contralateral vessels (13% versus 4%; P = .06). After adjustment for age, sex, diabetes mellitus, and degree of stenosis, intraplaque hemorrhage was associated with disrupted plaque surface (OR, 3.13; 95% CI, 1.25-7.84) in all vessels.

CONCLUSIONS

Intraplaque hemorrhage is associated with disruption of the plaque surface in patients with a carotid artery stenosis of <70%. Serial studies are needed to investigate whether intraplaque hemorrhage indeed increases the risk of plaque rupture and subsequent ischemic stroke during follow-up.

Angiopoietin-2 blocking antibodies reduce early atherosclerotic plaque development in mice

OBJECTIVE

Angiopoietin-2 (Ang-2) blocking agents are currently undergoing clinical trials for use in cancer treatment. Ang-2 has also been associated with rupture-prone atherosclerotic plaques in humans, suggesting a role for Ang-2 in plaque stability. Despite the availability of Ang-2 blocking agents, their clinical use is still lacking. Our aim was to establish if Ang-2 has a role in atheroma development and in the transition of subclinical to clinically relevant atherosclerosis. We investigated the effect of antibody-mediated Ang-2 blockage on atherogenesis after in a mouse model of atherosclerosis.

METHODS

Hypercholesterolemic (low-density lipoprotein receptor(-/-) apolipoprotein B(100/100)) mice were subjected to high-cholesterol diet for eight weeks, one group with and one group without Ang-2 blocking antibody treatment during weeks 4-8.To enhance plaque development, a peri-adventitial collar was placed around the carotid arteries at the start of antibody treatment. Aortic root, carotid arteries and brachiocephalic arteries were analyzed to evaluate the effect of Ang-2 blockage on atherosclerotic plaque size and stable plaque characteristics.

RESULTS

Anti-Ang-2 treatment reduced the size of fatty streaks in the brachiocephalic artery (-72%, p < 0.05). In addition, antibody-mediated Ang-2 blockage reduced plasma triglycerides (-27%, p < 0.05). In contrast, Ang-2 blockage did not have any effect on the size or composition (collagen content, macrophage percentage, adventitial microvessel density) of pre-existing plaques in the aortic root or collar-induced plaques in the carotid artery.

CONCLUSIONS

Ang-2 blockage was beneficial as it decreased fatty streak formation and plasma triglyceride levels, but had no adverse effect on pre-existing atherosclerosis in hypercholesterolemic mice.

Foam Cell Formation In Vivo Converts Macrophages to a Pro-Fibrotic Phenotype

Formation of foam cell macrophages, which sequester extracellular modified lipids, is a key event in atherosclerosis. How lipid loading affects macrophage phenotype is controversial, with evidence suggesting either pro- or anti-inflammatory consequences. To investigate this further, we compared the transcriptomes of foamy and non-foamy macrophages that accumulate in the subcutaneous granulomas of fed-fat ApoE null mice and normal chow fed wild-type mice in vivo. Consistent with previous studies, LXR/RXR pathway genes were significantly over-represented among the genes up-regulated in foam cell macrophages. Unexpectedly, the hepatic fibrosis pathway, associated with platelet derived growth factor and transforming growth factor-β action, was also over-represented. Several collagen polypeptides and proteoglycan core proteins as well as connective tissue growth factor and fibrosis-related FOS and JUN transcription factors were up-regulated in foam cell macrophages. Increased expression of several of these genes was confirmed at the protein level in foam cell macrophages from subcutaneous granulomas and in atherosclerotic plaques. Moreover, phosphorylation and nuclear translocation of SMAD2, which is downstream of several transforming growth factor-β family members, was also detected in foam cell macrophages. We conclude that foam cell formation in vivo leads to a pro-fibrotic macrophage phenotype, which could contribute to plaque stability, especially in early lesions that have few vascular smooth muscle cells.

Quantification of bound microbubbles in ultrasound molecular imaging

Molecular markers associated with diseases can be visualized and quantified noninvasively with targeted ultrasound contrast agent (t-UCA) consisting of microbubbles (MBs) that can bind to specific molecular targets. Techniques used for quantifying t-UCA assume that all unbound MBs are taken out of the blood pool few minutes after injection and only MBs bound to the molecular markers remain. However, differences in physiology, diseases, and experimental conditions can increase the longevity of unbound MBs. In such conditions, unbound MBs will falsely be quantified as bound MBs. We have developed a novel technique to distinguish and classify bound from unbound MBs. In the post-processing steps, first, tissue motion was compensated using block-matching (BM) techniques. To preserve only stationary contrast signals, a minimum intensity projection (MinIP) or 20th-percentile intensity projection (PerIP) was applied. The after-flash MinIP or PerIP was subtracted from the before-flash MinIP or PerIP. In this way, tissue artifacts in contrast images were suppressed. In the next step, bound MB candidates were detected. Finally, detected objects were tracked to classify the candidates as unbound or bound MBs based on their displacement. This technique was validated in vitro, followed by two in vivo experiments in mice. Tumors (n = 2) and salivary glands of hypercholesterolemic mice (n = 8) were imaged using a commercially available scanner. Boluses of 100 μL of a commercially available t-UCA targeted to angiogenesis markers and untargeted control UCA were injected separately. Our results show considerable reduction in misclassification of unbound MBs as bound ones. Using our method, the ratio of bound MBs in salivary gland for images with targeted UCA versus control UCA was improved by up to two times compared with unprocessed images.

Between Rho(k) and a hard place: the relation between vessel wall stiffness, endothelial contractility, and cardiovascular disease

Vascular stiffness is a mechanical property of the vessel wall that affects blood pressure, permeability, and inflammation. As a result, vascular stiffness is a key driver of (chronic) human disorders, including pulmonary arterial hypertension, kidney disease, and atherosclerosis. Responses of the endothelium to stiffening involve integration of mechanical cues from various sources, including the extracellular matrix, smooth muscle cells, and the forces that derive from shear stress of blood. This response in turn affects endothelial cell contractility, which is an important property that regulates endothelial stiffness, permeability, and leukocyte-vessel wall interactions. Moreover, endothelial stiffening reduces nitric oxide production, which promotes smooth muscle cell contraction and vasoconstriction. In fact, vessel wall stiffening, and microcirculatory endothelial dysfunction, precedes hypertension and thus underlies the development of vascular disease. Here, we review the cross talk among vessel wall stiffening, endothelial contractility, and vascular disease, which is controlled by Rho-driven actomyosin contractility and cellular mechanotransduction. In addition to discussing the various inputs and relevant molecular events in the endothelium, we address which actomyosin-regulated changes at cell adhesion complexes are genetically associated with human cardiovascular disease. Finally, we discuss recent findings that broaden therapeutic options for targeting this important mechanical signaling pathway in vascular pathogenesis.

Evaluation of iron oxide nanoparticle micelles for magnetic particle imaging (MPI) of thrombosis

Magnetic particle imaging (MPI) is an emerging medical imaging modality that directly visualizes magnetic particles in a hot-spot like fashion. We recently developed an iron oxide nanoparticle-micelle (ION-Micelle) platform that allows highly sensitive MPI. The goal of this study was to assess the potential of the ION-Micelles for MPI-based detection of thrombi. To this aim, an in vivo carotid artery thrombosis mouse model was employed and ex vivo magnetic particle spectrometer (MPS) measurements of the carotid arteries were performed. In addition, we studied the effect of functionalization of the ION-Micelle nanoplatform with fibrin-binding peptides (FibPeps) with respect to nanoparticle thrombus uptake and hence thrombus detection. In vivo quantitative MR imaging pre- and post-ION-Micelle injection was performed as reference for visualization of ION-micelle uptake. ION-Micelles significantly decreased T₂ values in the thrombi with respect to pre-injection T₂ values (p < 0.01) and significantly increased ex vivo MPS thrombus signal with respect to the noninjured, contralateral carotid (p < 0.01). Functionalization of the ION-Micelles with the FibPep peptides did not result in an increased MPS thrombus signal with respect to the non-fibrin binding ION-Micelles. The lack of a significant increased thrombus uptake for the FibPep-ION-Micelles indicates that (non-fibrin-specific) entrapment of nanoparticles in the mesh-like thrombi is the key contributor to thrombus nanoparticle uptake. Therefore, (nontargeted) ION-Micelles might be of value for noninvasive MPI-based diagnosis, characterization and treatment monitoring of thrombosis.

Imaging the intracranial atherosclerotic vessel wall using 7T MRI: initial comparison with histopathology

BACKGROUND AND PURPOSE

Several studies have attempted to characterize intracranial atherosclerotic plaques by using MR imaging sequences. However, dedicated validation of these sequences with histology has not yet been performed. The current study assessed the ability of ultra-high-resolution 7T MR imaging sequences with different image contrast weightings to image plaque components, by using histology as criterion standard.

MATERIALS AND METHODS

Five specimens of the circle of Wills were imaged at 7T with 0.11 × 0.11 mm in-plane-resolution proton attenuation-, T1-, T2-, and T2*-weighted sequences (through-plane resolution, 0.11-1 mm). Tissue samples from 13 fiducial-marked locations (per specimen) on MR imaging underwent histologic processing and atherosclerotic plaque classification. Reconstructed MR images were matched with histologic sections at corresponding locations.

RESULTS

Forty-four samples were available for subsequent evaluation of agreement or disagreement between plaque components and image contrast differences. Of samples, 52.3% (n = 23) showed no image contrast heterogeneity; this group comprised solely no lesions or early lesions. Of samples, 25.0% (n = 11, mostly advanced lesions) showed good correlation between the spatial organization of MR imaging heterogeneities and plaque components. Areas of foamy macrophages were generally seen as proton attenuation-, T2-, and T2*- hypointense areas, while areas of increased collagen content showed more ambiguous signal intensities. Five samples showed image-contrast heterogeneity without corresponding plaque components on histology; 5 other samples showed contrast heterogeneity based on intima-media artifacts.

CONCLUSIONS

MR imaging at 7T has the image contrast capable of identifying both focal intracranial vessel wall thickening and distinguishing areas of different signal intensities spatially corresponding to plaque components within more advanced atherosclerotic plaques.

Reversal of hypoxia in murine atherosclerosis prevents necrotic core expansion by enhancing efferocytosis

OBJECTIVE

Advanced murine and human plaques are hypoxic, but it remains unclear whether plaque hypoxia is causally related to atherogenesis. Here, we test the hypothesis that reversal of hypoxia in atherosclerotic plaques by breathing hyperoxic carbogen gas will prevent atherosclerosis.

APPROACH AND RESULTS

Low-density lipoprotein receptor-deficient mice (LDLR(-/-)) were fed a Western-type diet, exposed to carbogen (95% O2, 5% CO2) or air, and the effect on plaque hypoxia, size, and phenotype was studied. First, the hypoxic marker pimonidazole was detected in murine LDLR(-/-) plaque macrophages from plaque initiation onwards. Second, the efficacy of breathing carbogen (90 minutes, single exposure) was studied. Compared with air, carbogen increased arterial blood pO2 5-fold in LDLR(-/-) mice and reduced plaque hypoxia in advanced plaques of the aortic root (-32%) and arch (-84%). Finally, the effect of repeated carbogen exposure on progression of atherosclerosis was studied in LDLR(-/-) mice fed a Western-type diet for an initial 4 weeks, followed by 4 weeks of diet and carbogen or air (both 90 min/d). Carbogen reduced plaque hypoxia (-40%), necrotic core size (-37%), and TUNEL(+) (terminal uridine nick-end labeling positive) apoptotic cell content (-50%) and increased efferocytosis of apoptotic cells by cluster of differentiation 107b(+) (CD107b, MAC3) macrophages (+36%) in advanced plaques of the aortic root. Plaque size, plasma cholesterol, hematopoiesis, and systemic inflammation were unchanged. In vitro, hypoxia hampered efferocytosis by bone marrow-derived macrophages, which was dependent on the receptor Mer tyrosine kinase.

CONCLUSIONS

Carbogen restored murine plaque oxygenation and prevented necrotic core expansion by enhancing efferocytosis, likely via Mer tyrosine kinase. Thus, plaque hypoxia is causally related to necrotic core expansion.

Biomechanical factors in atherosclerosis: mechanisms and clinical implications

Blood vessels are exposed to multiple mechanical forces that are exerted on the vessel wall (radial, circumferential and longitudinal forces) or on the endothelial surface (shear stress). The stresses and strains experienced by arteries influence the initiation of atherosclerotic lesions, which develop at regions of arteries that are exposed to complex blood flow. In addition, plaque progression and eventually plaque rupture is influenced by a complex interaction between biological and mechanical factors-mechanical forces regulate the cellular and molecular composition of plaques and, conversely, the composition of plaques determines their ability to withstand mechanical load. A deeper understanding of these interactions is essential for designing new therapeutic strategies to prevent lesion development and promote plaque stabilization. Moreover, integrating clinical imaging techniques with finite element modelling techniques allows for detailed examination of local morphological and biomechanical characteristics of atherosclerotic lesions that may be of help in prediction of future events. In this ESC Position Paper on biomechanical factors in atherosclerosis, we summarize the current 'state of the art' on the interface between mechanical forces and atherosclerotic plaque biology and identify potential clinical applications and key questions for future research.

Assessment of middle cerebral artery diameter during hypocapnia and hypercapnia in humans using ultra-high-field MRI

In the evaluation of cerebrovascular CO2 reactivity measurements, it is often assumed that the diameter of the large intracranial arteries insonated by transcranial Doppler remains unaffected by changes in arterial CO2 partial pressure. However, the strong cerebral vasodilatory capacity of CO2 challenges this assumption, suggesting that there should be some changes in diameter, even if very small. Data from previous studies on effects of CO2 on cerebral artery diameter [middle cerebral artery (MCA)] have been inconsistent. In this study, we examined 10 healthy subjects (5 women, 5 men, age 21-30 yr). High-resolution (0.2 mm in-plane) MRI scans at 7 Tesla were used for direct observation of the MCA diameter during hypocapnia, -1 kPa (-7.5 mmHg), normocapnia, 0 kPa (0 mmHg), and two levels of hypercapnia, +1 and +2 kPa (7.5 and 15 mmHg), with respect to baseline. The vessel lumen was manually delineated by two independent observers. The results showed that the MCA diameter increased by 6.8 ± 2.9% in response to 2 kPa end-tidal P(CO2) (PET(CO2)) above baseline. However, no significant changes in diameter were observed at the -1 kPa (-1.2 ± 2.4%), and +1 kPa (+1.4 ± 3.2%) levels relative to normocapnia. The nonlinear response of the MCA diameter to CO2 was fitted as a continuous calibration curve. Cerebral blood flow changes measured by transcranial Doppler could be corrected by this calibration curve using concomitant PET(CO2) measurements. In conclusion, the MCA diameter remains constant during small deviations of the PET(CO2) from normocapnia, but increases at higher PET(CO2) values.

F-actin-anchored focal adhesions distinguish endothelial phenotypes of human arteries and veins

OBJECTIVE

Vascular endothelial-cadherin- and integrin-based cell adhesions are crucial for endothelial barrier function. Formation and disassembly of these adhesions controls endothelial remodeling during vascular repair, angiogenesis, and inflammation. In vitro studies indicate that vascular cytokines control adhesion through regulation of the actin cytoskeleton, but it remains unknown whether such regulation occurs in human vessels. We aimed to investigate regulation of the actin cytoskeleton and cell adhesions within the endothelium of human arteries and veins.

APPROACH AND RESULTS

We used an ex vivo protocol for immunofluorescence in human vessels, allowing detailed en face microscopy of endothelial monolayers. We compared arteries and veins of the umbilical cord and mesenteric, epigastric, and breast tissues and find that the presence of central F-actin fibers distinguishes the endothelial phenotype of adult arteries from veins. F-actin in endothelium of adult veins as well as in umbilical vasculature predominantly localizes cortically at the cell boundaries. By contrast, prominent endothelial F-actin fibers in adult arteries anchor mostly to focal adhesions containing integrin-binding proteins paxillin and focal adhesion kinase and follow the orientation of the extracellular matrix protein fibronectin. Other arterial F-actin fibers end in vascular endothelial-cadherin-based endothelial focal adherens junctions. In vitro adhesion experiments on compliant substrates demonstrate that formation of focal adhesions is strongly induced by extracellular matrix rigidity, irrespective of arterial or venous origin of endothelial cells.

CONCLUSIONS

Our data show that F-actin-anchored focal adhesions distinguish endothelial phenotypes of human arteries from veins. We conclude that the biomechanical properties of the vascular extracellular matrix determine this endothelial characteristic.

SPECT imaging of fibrin using fibrin-binding peptides

Noninvasive detection of fibrin in vivo using diagnostic imaging modalities may improve clinical decision-making on possible therapeutic options in atherosclerosis, cancer and thrombus-related pathologies such as pulmonary embolism and deep venous thrombosis. The aim of this study was to assess the potential of a novel (111)In-labeled fibrin-binding peptide (FibPep) to visualize thrombi in mice noninvasively using single-photon emission computed tomography (SPECT). FibPep and a negative control peptide (NCFibPep) were synthesized and their fibrin-binding properties were assessed in vitro. FibPep showed enhanced binding compared with NCFibPep to both fibrin and blood clots. FibPep bound to fibrin with a dissociation constant (K(d)) of 0.8 μ m, whereas NCFibPep displayed at least a 100-fold lower affinity towards fibrin. A FeCl3 -injury carotid artery thrombosis mouse model was used to evaluate the peptides in vivo. FibPep and NCFibPep displayed rapid blood clearance and were eliminated via the renal pathway. In vivo SPECT imaging using FibPep allowed clear visualization of thrombi. Ex vivo biodistribution showed significantly increased uptake of FibPep in the thrombus-containing carotid in comparison to the noninjured carotid (5.7 ± 0.7 and 0.6 ± 0.4% injected dose per gram (%ID g(-1)), respectively; p < 0.01; n = 4), whereas nonspecific NCFibPep did not (0.4 ± 0.2 and 0.3 ± 0.0%ID g(-1), respectively; n = 4). In conclusion, FibPep displayed high affinity towards fibrin in vitro and rapid blood clearance in vivo, and allowed sensitive detection of thrombi using SPECT imaging. Therefore, this particular imaging approach may provide a new tool to diagnose and monitor diseases such as atherosclerosis and cancer.