Osteogenesis associates with inflammation in early-stage atherosclerosis evaluated by molecular imaging in vivo

Carbonic Anhydrase 1-Mediated Calcification Is Associated With Atherosclerosis, and Methazolamide Alleviates Its Pathogenesis

Vascular calcification is an important pathogenic process in atherosclerosis (AS); however, its immediate cause is unknown. Our previous study demonstrated that carbonic anhydrase 1 (CA1) stimulates ossification and calcification in ankylosing spondylitis and breast cancer. The current study investigated whether CA1 plays an important role in AS calcification and whether the CA inhibitor methazolamide (MTZ) has a therapeutic effect on AS. We successfully established an AS model by administration of a high-fat diet to apolipoprotein E (ApoE^−/−) mice. The treated animals had significantly increased serum levels of high-density lipoprotein cholesterol (HDL-c) and nitric oxide (NO) and decreased serum concentrations of total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-c), interleukin (IL-6), interferon (IFN)-γ, granulocyte-macrophage colony-stimulating factor (GM-CSF), tumor necrosis factor-α (TNF-α), chemokine (C-X-C motif) ligand 1/keratinocyte-derived chemokine (CXCL1/KC), and C-C motif chemokine ligand 2 (CCL2)/monocyte chemoattractant protein 1 (MCP-1). The treated mice also had reduced AS plaque areas and fat accumulation, with no clear calcium deposition in the intima of the blood vessels. CA1 expression was significantly increased in the aortic lesions, particularly in calcified regions, but the expression was dramatically lower in the mice that received MTZ treatment or MTZ preventive treatment. CA1 was also highly expressed in human AS tissues and in rat vascular smooth muscle cells (VSMCs) with β-glycerophosphate (㒐β-GP)-induced calcification. Acetazolamide (AZ), a CA inhibitor with a chemical structure similar to MTZ, markedly suppressed calcification and reduced CA1, IL-6, IFN-γ, GM-CSF, and TNF-α expression in cultured VSMCs. Anti-CA1 small interfering ribonucleic acid (siRNA) significantly suppressed calcification, cell proliferation, and migration, promoted apoptosis, and reduced IL-6, IFN-γ, GM-CSF, and TNF-α secretion in cultured VSMCs. These results demonstrated that CA1 expression and CA1-mediated calcification are significantly associated with AS progression. MTZ significantly alleviated AS and suppressed CA1 expression and proinflammatory cytokine secretion, indicating the potential use of this drug for AS treatment.

Impact of Femoral Ossification on Local and Systemic Cardiovascular Patients' Condition

BACKGROUND

Vascular calcifications are associated with a high cardiovascular morbi-mortality in the coronary territory. In parallel, femoral arteries are more calcified and develop osteoid metaplasia (OM). This study was conducted to assess the predictive value of OM and local inflammation on the occurrence of mid- and long-term adverse cardiovascular events.

METHOD

Between 2008 and 2015, 86 atheromatous samples were harvested during femoral endarterectomy on 81 patients and processed for histomorphological analyses of calcifications and inflammation (monocytes and B cells). Histological findings were compared with the long-term follow-up of patients, including major adverse cardiac event (MACE), major adverse limb event (MALE), and mortality. Frequencies were presented as percentage, and continuous data, as mean and standard deviation. A P-value < 0.05 was considered statistically significant.

RESULTS

Median follow-up was 42.4 months (26.9-58.8). Twenty-eight percent of patients underwent a MACE; a MALE occurred in 18 (21%) limbs. Survival rate was 87.2% at 36 months. OM was found in 41 samples (51%), without any significant impact on the occurrence of MACE, MALE, or mortality. Preoperative white blood cell formulae revealed a higher rate of neutrophils associated with MACE (P = 0.04) and MALE (P = 0.0008), correlated with higher B cells counts in plaque samples.

CONCLUSIONS

OM is part of femoral calcifications in almost 50% of the cases but does not seem to be an independent predictive variable for MACE or MALE. However, a higher rate of B cell infiltration of the plaque and preoperative neutrophil blood count may be predictive of adverse events during follow-up.

Correlation of computed tomography with carotid plaque transcriptomes associates calcification with lesion-stabilization

BACKGROUND AND AIMS

Unstable carotid atherosclerosis causes stroke, but methods to identify patients and lesions at risk are lacking. We recently found enrichment of genes associated with calcification in carotid plaques from asymptomatic patients. Here, we hypothesized that calcification represents a stabilising feature of plaques and investigated how macro-calcification, as estimated by computed tomography (CT), correlates with gene expression profiles in lesions.

METHODS

Plaque calcification was measured in pre-operative CT angiographies. Plaques were sorted into high- and low-calcified, profiled with microarrays, followed by bioinformatic analyses. Immunohistochemistry and qPCR were performed to evaluate the findings in plaques and arteries with medial calcification from chronic kidney disease patients.

RESULTS

Smooth muscle cell (SMC) markers were upregulated in high-calcified plaques and calcified plaques from symptomatic patients, whereas macrophage markers were downregulated. The most enriched processes in high-calcified plaques were related to SMCs and extracellular matrix (ECM) organization, while inflammation, lipid transport and chemokine signaling were repressed. These findings were confirmed in arteries with high medial calcification. Proteoglycan 4 (PRG4) was identified as the most upregulated gene in association with plaque calcification and found in the ECM, SMA+ and CD68+/TRAP + cells.

CONCLUSIONS

Macro-calcification in carotid lesions correlated with a transcriptional profile typical for stable plaques, with altered SMC phenotype and ECM composition and repressed inflammation. PRG4, previously not described in atherosclerosis, was enriched in the calcified ECM and localized to activated macrophages and smooth muscle-like cells. This study strengthens the notion that assessment of calcification may aid evaluation of plaque phenotype and stroke risk.

In times of tobacco-free nicotine consumption: The influence of nicotine on vascular calcification

BACKGROUND

Smoking remains the most important avoidable cause of global mortality. Even though the number of cigarette smokers declines in first world countries, the uses of alternative nicotine delivery products increase and may even surpass the sells of cigarettes. In this light, the explicit role of nicotine in the development of cardiovascular diseases should be elucidated.

OBJECTIVES

This narrative review attempts to connect current literature about possible effects of nicotine on the environment of the vasculature to the pathogenesis of vascular calcification, focusing on the tunica media of the vessel wall.

METHODS

For this review, papers found on Pubmed and Medline until December 2018 by searching for the keywords nicotine, vascular calcification, oxidative stress, osteoblastic transdifferentiation and matrix degradation were considered.

RESULTS

Nicotine creates an environment that probably facilitates and maybe even induces osteogenic transdifferentiation of VSMC by inflammation, endothelial dysfunction and reactive oxygen species. This process is believed to be a key event in calcification of the tunica media of the vessel wall. Furthermore, nicotine could lead to the formation of nucleation sites for hydroxyapatite by facilitating matrix vesicles and extracellular matrix degradation.

CONCLUSIONS

There is a growing body of evidence implicating that nicotine alone could impair vascular function and lead to vascular calcification. Further research is necessary to elucidate the explicit influence of nicotine on arteriosclerosis.

Calcifications in atherosclerotic plaques and impact on plaque biomechanics

The catastrophic mechanical rupture of an atherosclerotic plaque is the underlying cause of the majority of cardiovascular events. The infestation of vascular calcification in the plaques creates a mechanically complex tissue composite. Local stress concentrations and plaque tissue strength properties are the governing parameters required to predict plaque ruptures. Advanced imaging techniques have permitted insight into fundamental mechanisms driving the initiating inflammatory-driven vascular calcification of the diseased intima at the (sub-) micron scale and up to the macroscale. Clinical studies have potentiated the biomechanical relevance of calcification through the derivation of links between local plaque rupture and specific macrocalcification geometrical features. The clinical implications of the data presented in this review indicate that the combination of imaging, experimental testing, and computational modelling efforts are crucial to predict the rupture risk for atherosclerotic plaques. Specialised experimental tests and modelling efforts have further enhanced the knowledge base for calcified plaque tissue mechanical properties. However, capturing the temporal instability and rupture causality in the plaque fibrous caps remains elusive. Is it necessary to move our experimental efforts down in scale towards the fundamental (sub-) micron scales in order to interpret the true mechanical behaviour of calcified plaque tissue interactions that is presented on a macroscale in the clinic and to further optimally assess calcified plaques in the context of biomechanical modelling.

MSC-derived sEVs enhance patency and inhibit calcification of synthetic vascular grafts by immunomodulation in a rat model of hyperlipidemia

Vascular grafts often exhibit low patency rates in clinical settings due to the pathological environment within the patients requiring the surgery. Mesenchymal stem cell (MSC)-derived small extracellular vesicles (sEVs) have attracted increasing attention. These sEVs contain many potent signaling molecules that play important roles in tissue regeneration, such as microRNA and cytokines. In this study, a sEVs-functionalized vascular graft was developed, and in vivo performance was systematically evaluated in a rat model of hyperlipidemia. Electrospun poly (ε-caprolactone) (PCL) vascular grafts were first modified with heparin, to enhance the anti-thrombogenicity. MSC-derived sEVs were loaded onto the heparinized PCL grafts to obtain functional vascular grafts. As-prepared vascular grafts were implanted to replace a segment of rat abdominal artery (1 cm) for up to 3 months. Results showed that the incorporation of MSC-derived sEVs effectively inhibited thrombosis and calcification, thus enhancing the patency of vascular grafts. Furthermore, regeneration of the endothelium and vascular smooth muscle was markedly enhanced, as attributed to the bioactive molecules within the sEVs, including vascular endothelial growth factor (VEGF), miRNA126, and miRNA145. More importantly, MSC-derived sEVs demonstrated a robust immunomodulatory effect, that is, they induced the transition of macrophages from a pro-inflammatory and atherogenic (M1) phenotype to an anti-inflammatory and anti-osteogenic (M2c) phenotype. This phenotypic switch was confirmed in both in vitro and in vivo analyses. Taken together, these results suggest that fabrication of vascular grafts with immunomodulatory function can provide an effective approach to improve vascular performance and functionality, with translational implication in cardiovascular regenerative medicine.

Graded murine wire-induced aortic valve stenosis model mimics human functional and morphological disease phenotype

Aortic valve stenosis (AS) is the most common valve disease requiring therapeutic intervention. Even though the incidence of AS has been continuously rising and AS is associated with significant morbidity and mortality, to date, no medical treatments have been identified that can modify disease progression. This unmet medical need is likely attributed to an incomplete understanding of the molecular mechanism driving disease development. To investigate the pathophysiology leading to AS, reliable and reproducible animal models that mimic human pathophysiology are needed. We have tested and expanded the protocols of a wire-injury induced AS mouse model. For this model, coronary wires were used to apply shear stress to the aortic valve cusps with increasing intensity. These protocols allowed distinction of mild, moderate and severe wire-injury. Upon moderate or severe injury, AS developed with a significant increase in aortic valve peak blood flow velocity. While moderate injury promoted solitary AS, severe-injury induced mixed aortic valve disease with concomitant mild to moderate aortic regurgitation. The changes in aortic valve function were reflected by dilation and hypertrophy of the left ventricle, as well as a decreased left ventricular ejection fraction. Histological analysis revealed the classic hallmarks of human disease with aortic valve thickening, increased macrophage infiltration, fibrosis and calcification. This new mouse model of AS promotes functional and morphological changes similar to moderate and severe human AS. It can be used to investigate the pathomechanisms contributing to AS development and to test novel therapeutic strategies.

Peri-Coronary Adipose Tissue Density Is Associated With 18F-Sodium Fluoride Coronary Uptake in Stable Patients With High-Risk Plaques

OBJECTIVES

This study aimed to assess the association between increased lesion peri-coronary adipose tissue (PCAT) density and coronary ¹⁸F-sodium fluoride (¹⁸F-NaF) uptake on positron emission tomography (PET) in stable patients with high-risk coronary plaques (HRPs) shown on coronary computed tomography angiography (CTA).

BACKGROUND

Coronary ¹⁸F-NaF uptake reflects the rate of calcification of coronary atherosclerotic plaque. Increased PCAT density is associated with vascular inflammation. Currently, the relationship between increased PCAT density and ¹⁸F-NaF uptake in stable patients with HRPs on coronary CTA has not been characterized.

METHODS

Patients who underwent coronary CTA were screened for HRP, which was defined by 3 concurrent plaque features: positive remodeling; low attenuation plaque (LAP) (<30 Hounsfield units [HU]) and spotty calcification; and obstructive coronary stenosis ≥50% (plaque volume >100 mm³). Patients with HRPs were recruited to undergo ¹⁸F-NaF PET/CT. In lesions with stenosis ≥25%, quantitative plaque analysis, mean PCAT density, maximal coronary motion-corrected ¹⁸F-NaF standard uptake values (SUVmax), and target-to-background ratios (TBR) were measured.

RESULTS

Forty-one patients (age 65 ± 6 years; 68% men) were recruited. Fifty-one lesions in 23 patients (56%) showed increased coronary ¹⁸F-NaF activity. Lesions with ¹⁸F-NaF uptake had higher surrounding PCAT density than those without ¹⁸F-NaF uptake (-73 HU; interquartile range -79 to -68 HU vs. -86 HU; interquartile range -94 to -80 HU; p < 0.001). ¹⁸F-NaF TBR and SUVmax were correlated with PCAT density (r = 0.63 and r = 0.68, respectively; all p < 0.001). On adjusted multiple regression analysis, increased lesion PCAT density and LAP volume were associated with ¹⁸F-NaF TBR (β = 0.25; 95% confidence interval: 0.17 to 0.34; p < 0.001 for PCAT, and β = 0.07; 95% confidence interval: 0.03 to 0.11; p = 0.002 for LAP).

CONCLUSIONS

In patients with HRP features on coronary CTA, increased density of PCAT was associated with focal ¹⁸F-NaF PET uptake. Simultaneous assessment of these imaging biomarkers by ¹⁸F-NaF PET and CTA might refine cardiovascular risk prediction in stable patients with HRP features.

18 F-Sodium Fluoride Imaging of Coronary Atherosclerosis in Ambulatory Patients With Diabetes Mellitus

Objective—

Although patients with diabetes mellitus (DM) are considered at high risk of cardiovascular events, there is growing evidence that this notion is incorrect. Atherosclerosis imaging may identify patients at risk.

Approach and Results—

We performed coronary atherosclerosis with 18 F-sodium fluoride (NaF) positron emission tomography/computed tomography and gated chest computed tomography for coronary artery calcium in 88 consecutive ambulatory patients with DM on a stable medical regimen. NaF has been shown to localize avidly in culprit lesions of patients with acute coronary syndromes and may identify unstable plaques. NaF activity was measured as target (coronary arteries)-to-background (left ventricular pool) ratio (TBR). High TBR was defined as ≥1.5. The mean age of the cohort was 54±14 years, 55% had type 2 DM, 65% were men, the median HgbA1c (hemoglobin A1c) and LDL (low-density lipoprotein) cholesterol were 7.5% (interquartile range, 7.1–8.5) and 1.9 mmol/L (interquartile range, 1.5–2.6), respectively. Mean coronary artery calcium score was 374±773, and median TBR was 1.2. Coronary artery TBR ≥1.5 was detected in 13 (15%) patients. In univariable analyses, male sex ( P =0.0002), estimated glomerular filtration rate ( P =0.02), and total coronary artery calcium score ( P =0.04) were associated with TBR. In multivariable analyses, TBR >median was associated with male sex ( P =0.0001) and statin use ( P =0.042).

Conclusions—

In ambulatory patients with DM asymptomatic for cardiovascular disease, the prevalence of potentially vulnerable plaques detected with NaF was low, but in the absence of follow-up data at this stage, we cannot assess the import of this information. Future research will establish whether NaF imaging helps risk stratify patients with DM.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT03530176.

Chronic Kidney Disease Is Linked to Carotid Nodular Calcification, An Unstable Plaque Not Correlated to Inflammation

The incidence and the different type of carotid calcifications, nodular and non-nodular, and their role in the acute cerebrovascular disease has not yet been defined. Various studies have correlated the presence of specific risk factors, in particular the chronic kidney disease, with the presence of calcification, but not with the type of calcification. Since it is likely that carotid nodular calcifications rather than those with non-nodular aspect may represent a plaque at high risk of rupture, the purpose of our study was to evaluate the role of nodular calcification in the pathogenesis of cerebrovascular syndromes and their possible correlation with specific risk factors. A total of 168 carotid plaques from symptomatic and asymptomatic patients submitted to endarterectomy, whom complete clinical and laboratory assessment of major cardiovascular risk factors was available, were studied. In 21 endarterectomies (5 from symptomatic and 16 from asymptomatic patients) an eruptive calcified nodule, consisting of calcified plates associated to a small amount of fibrous tissue without extracellular lipids and inflammatory cells, was found protruding into the lumen. Nodular calcifications were significantly observed in patients affected by chronic kidney disease (with GFR<60 ml / min / 1.73 m²), with a normal lipidic and glycemic profile. On the contrary, non-nodular calcification, mainly correlated to diabetes, were stable lesions. Results of our study suggest that the mechanisms and the clinical significance of carotid atherosclerotic calcification may be different. The nodular calcification could represent a type of unstable plaque, significantly related to chronic kidney disease, without inflammation, morphologically different from the classical vulnerable plaques.

Determination of Ultrastructural Properties of Human Carotid Atherosclerotic Plaques by Scanning Acoustic Microscopy, Micro-Computer Tomography, Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy

Microcalcification is the precursor of vulnerability of plaques in humans. Visualization of such small structures in vivo with high spatial resolution is an unsolved issue. The goal of this study is to evaluate the potential of scanning acoustic microscopy (SAM) in the determination of atherosclerotic plaques with calcifications by validating this technique with micro-computer tomography (micro-CT), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The fibrocalcific plaques were obtained from 12 different patients and initially examined with micro-CT. The images exhibited calcifications within these plaques. For imaging with SAM, approximately 5 μm thick slices were prepared. Sound speed values within calcified regions were measured to be greater than the ones in collagen-rich regions. These fibrocalcific plaques were also examined with SEM and EDS revealing collagen and calcium deposition within these samples. The consistency of the results obtained by all of the modalities involved in our study is an indication of the potential of SAM as a clinical tool for the diagnosis of vulnerable plaques.

Relationship between Aortic Arch Calcification, Detected by Chest X-Ray, and Renal Resistive Index in Patients with Hypertension

OBJECTIVE

Aortic arch calcification (AAC) is a surrogate marker for arterial stiffness and hypertension-related vascular damage. Renal resistive index (RRI), a renal Doppler ultrasonography parameter, is used to assess renal hemodynamics. In this study, we aimed to evaluate the relationship between RRI and AAC in patients with hypertension.

METHODS

Patients with hypertension underwent a chest X-ray and re nal Doppler ultrasonography. They were divided into two groups according to RRI (group 1: RRI ≥0.70; group 2: RRI < 0.70). Two examiners, blinded to the findings of RRI, reviewed the AAC in these patients. The kappa value was detected to be 0.781 and a p value < 0.001 was considered significant.

RESULTS

The study included 289 hypertensive patients (mean age 63.87 ± 11.38 years). In 53.6% (n = 155) of the study subjects, RRI was observed to be ≥0.70. Patients with RRI ≥70 were older and had more prevalent AAC as well as left ventricular hypertrophy. A multiple linear regression analysis was carried out to test whether presence of AAC significantly predicted RRI. The results of the regression analysis indicated that presence of AAC significantly predicted RRI (β = 0.053; p < 0.001).

CONCLUSIONS

A strong and independent relationship was found between AAC on chest X-ray and RRI in patients with hypertension.

Detection of Calcified Aortic Plaques in an Apolipoprotein E Animal Model Using a Human Computed Tomography System for Ultra-High-resolution Imaging: A Feasibility Study

PURPOSE

The purpose of this study was to prospectively evaluate the feasibility of detecting calcified aortic plaques in apolipoprotein E knockout (ApoE-KO) mice using a state-of-the-art human computed tomography (CT) system.

MATERIALS AND METHODS

Eleven ApoE-KO and 9 wild-type mice, all male, were examined in this study. After intraperitoneal injection of 6.6% ketamine all mice underwent 2 ultra-high-resolution CT protocols on a third-generation dual-source CT system at 120 kVp and 130 kVp tube voltage, both performed with a tube current time product of 1300 mAs. Images (0.4 mm) with an increment of 0.2 mm were reconstructed using an iterative reconstruction algorithm. Calcium detectability and scores (Agatston, volume, mass) were determined with a dedicated human calcium scoring software (CaScoring). After the CT examination, a calcium quantification assay of the aortae was performed to determine the aortic calcium content of each mouse. The CT scan time ranged between 40 and 48 seconds. All mice survived the procedure.

RESULTS

Calcified plaques could be detected in 8 of 11 ApoE-KO mice. Quantification of calcium levels showed significant differences between those with morphologic calcium plaques detected in CT and those without (3.44±1.6 μg Ca/mg vs. 0.33±0.35 μg Ca/mg; P<0.05). The receiver-operating characteristics analysis revealed a total calcium cut-off value of 0.71 μg Ca/mg for the detection using calcium score algorithms (specificity: 100% and sensitivity: 90%).

CONCLUSION

Using a state-of-the-art human CT protocol and an in-human-established calcium scoring system allows for the detection and quantification of calcified aortic plaques in ApoE-KO mice. These results may facilitate preclinical imaging for translational and longitudinal atherosclerotic research studies.

Lipoproteins in Cardiovascular Calcification: Potential Targets and Challenges

Previously considered a degenerative process, cardiovascular calcification is now established as an active process that is regulated in several ways by lipids, phospholipids, and lipoproteins. These compounds serve many of the same functions in vascular and valvular calcification as they do in skeletal bone calcification. Hyperlipidemia leads to accumulation of lipoproteins in the subendothelial space of cardiovascular tissues, which leads to formation of mildly oxidized phospholipids, which are known bioactive factors in vascular cell calcification. One lipoprotein of particular interest is Lp(a), which showed genome-wide significance for the presence of aortic valve calcification and stenosis. It carries an important enzyme, autotaxin, which produces lysophosphatidic acid (LPA), and thus has a key role in inflammation among other functions. Matrix vesicles, extruded from the plasma membrane of cells, are the sites of initiation of mineral formation. Phosphatidylserine, a phospholipid in the membranes of matrix vesicles, is believed to complex with calcium and phosphate ions, creating a nidus for hydroxyapatite crystal formation in cardiovascular as well as in skeletal bone mineralization. This review focuses on the contributions of lipids, phospholipids, lipoproteins, and autotaxin in cardiovascular calcification, and discusses possible therapeutic targets.

Nanotechnology, an alternative with promising prospects and advantages for the treatment of cardiovascular diseases

Cardiovascular diseases (CVDs) are one of the most important causes of mortality and affecting the health status of patients. At the same time, CVDs cause a huge health and economic burden to the whole world. Although a variety of therapeutic drugs and measures have been produced to delay the progress of the disease and improve the quality of life of patients, most of the traditional therapeutic strategies can only cure the symptoms and cannot repair or regenerate the damaged ischemic myocardium. In addition, they may bring some unpleasant side effects. Therefore, it is vital to find and explore new technologies and drugs to solve the shortcomings of conventional treatments. Nanotechnology is a new way of using and manipulating the matter at the molecular scale, whose functional organization is measured in nanometers. Because nanoscale phenomena play an important role in cell signal transduction, enzyme action and cell cycle, nanotechnology is closely related to medical research. The application of nanotechnology in the field of medicine provides an alternative and novel direction for the treatment of CVDs, and shows excellent performance in the field of targeted drug therapy and the development of biomaterials. This review will briefly introduce the latest applications of nanotechnology in the diagnosis and treatment of common CVDs.

Co-localization of plaque macrophages with calcification is associated with a more vulnerable plaque phenotype and a greater calcification burden in coronary target segments as determined by OCT

BACKGROUND

The presence of plaque macrophages and microcalcifications are acknowledged features of plaque vulnerability. Experimental data suggest that microcalcifications promote inflammation and macrophages foster microcalcifications. However, co-localization of plaque macrophages and calcification (ColocCaMa) in coronary segments and its impact on plaque phenotype and lesion vulnerability is unexplored.

METHODS

Plaque morphology including ColocCaMa of calcified coronary target segments in patients with stable coronary artery disease (n = 116) was analyzed using optical coherence tomography (OCT) prior to coronary intervention. Therefore we considered macrophages co-localized with calcification if their distance in an OCT frame was <100μm and OCT-defined microcalcifications with a calcium arc <22.5°.

RESULTS

ColocCaMa was present in 29/116(25.0%) coronary segments. Calcium burden was greater (calcium volume index:1731±1421°*mm vs. 963±984°*mm, p = 0.002) and calcifications were more superficial (minimal thickness of the fibrous cap overlying the calcification 35±37μm vs. 64±72μm, p = 0.005) in the presence of ColocCaMa. Segments with ColocCaMa demonstrated a higher incidence of newly suggested features of plaque vulnerability, with a 3.5-fold higher number of OCT-defined microcalcifications (0.7±1.0 vs. 0.2±0.6, p = 0.022) and a 6.7-fold higher incidence of plaque inflammation (macrophage volume index:148.7±248.3°*mm vs. 22.2±57.4°*mm, p<0.001). Clinically, intima-media thickness (IMT) in carotid arteries was increased in patients with ColocCaMa (1.02±0.30mm vs. 0.85±0.18, p = 0.021). In a multivariate model, IMT (OR1.76 for 100μm, 95%CI 1.16-2.65, p = 0.007), HDL-cholesterol (OR0.36 for 10mg/dl, 95%CI 0.16-0.84, p = 0.017), calcium volume index (OR1.07 for 100°*mm, 95%CI 1.00-1.14, p = 0.049), macrophage volume index (OR5.77 for 100°*mm, 95%CI 2.04-16.3, p = 0.001) and minimal luminal area (OR3.41, 95%CI 1.49-7.78, p = 0.004) were independent predictors of ColocCaMa.

CONCLUSION

Plaque macrophages co-localize with calcifications in coronary target segments and this is associated with high-risk morphological features including microcalcifications and macrophage infiltration as well as with greater calcification burden. Our data may add to the understanding of the relationship between plaque macrophages, vascular calcification and their clinical impact.

Predictive Value of 18F-Sodium Fluoride Positron Emission Tomography in Detecting High-Risk Coronary Artery Disease in Combination With Computed Tomography

Background Application of 18F-sodium fluoride (18F-NaF) positron emission tomography ( PET ) to coronary artery disease has attracted interest. We investigated the utility of 18F-NaF uptake for predicting coronary events and evaluated the combined use of coronary computed tomography (CT) angiography ( CCTA ) and 18F-NaF PET /CT in coronary artery disease risk assessment. Methods and Results This study included patients with ≥1 coronary atherosclerotic lesion detected on CCTA who underwent 18F-NaF PET / CT . High-risk plaque on CCTA was defined as plaque with low density (<30 Hounsfield units) and high remodeling index (>1.1). Focal 18F-NaF uptake in each lesion was quantified using the maximum tissue:background ratio ( TBR max), and maximum TBR max per patient (M- TBR max) was determined. Thirty-two patients having a total of 112 analyzed lesions were followed for 2 years after 18F-NaF PET / CT scan, and 11 experienced coronary events (acute coronary syndrome and/or late coronary revascularization [after 3 months]). Patients with coronary events had higher M- TBR max than those without (1.39±0.18 versus 1.19±0.17, respectively; P=0.0034). The optimal M- TBR max cutoff to predict coronary events was 1.28 (area under curve: 0.79). Patients with M- TBR max ≥1.28 had a higher risk of earlier coronary events than those with lower M- TBR max ( P=0.0062 by log-rank test). In patient-based (n=41) and lesion-based (n=143) analyses of CCTA findings that predicted higher coronary 18F-NaF uptake, the presence of high-risk plaque was a significant predictor of both M- TBR max ≥1.28 and TBR max ≥1.28. Conclusions 18F-NaF PET / CT has the potential to detect high-risk coronary artery disease and individual coronary lesions and to predict future coronary events when combined with CCTA . Clinical Trial Registration URL : www.umin.ac.jp . Unique identifier: UMIN 000013735.

Target identification for the diagnosis and intervention of vulnerable atherosclerotic plaques beyond 18F-fluorodeoxyglucose positron emission tomography imaging: promising tracers on the horizon

Cardiovascular disease is the major cause of morbidity and mortality in developed countries and atherosclerosis is the major cause of cardiovascular disease. Atherosclerotic lesions obstruct blood flow in the arterial vessel wall and can rupture leading to the formation of occlusive thrombi. Conventional diagnostic tools are still of limited value for identifying the vulnerable arterial plaque and for predicting its risk of rupture and of releasing thromboembolic material. Knowledge of the molecular and biological processes implicated in the process of atherosclerosis will advance the development of imaging probes to differentiate the vulnerable plaque. The development of imaging probes with high sensitivity and specificity in identifying high-risk atherosclerotic vessel wall changes and plaques is crucial for improving knowledge-based decisions and tailored individual interventions. Arterial PET imaging with ¹⁸F-FDG has shown promising results in identifying inflammatory vessel wall changes in numerous studies and clinical trials. However, due to its limited specificity in general and its intense physiological uptake in the left ventricular myocardium that impair imaging of the coronary arteries, different PET tracers for the molecular imaging of atherosclerosis have been evaluated. This review describes biological, chemical and medical expertise supporting a translational approach that will enable the development of new or the evaluation of existing PET tracers for the identification of vulnerable atherosclerotic plaques for better risk prediction and benefit to patients.

Scanning Acoustic Microscopy and Time-Resolved Fluorescence Spectroscopy for Characterization of Atherosclerotic Plaques

Atherosclerotic plaques constitute the primary cause of heart attack and stroke. However, we still lack a clear identification of the plaques. Here, we evaluate the feasibility of scanning acoustic microscopy (SAM) and time-resolved fluorescence spectroscopy (TRFS) in atherosclerotic plaque characterization. We perform dual-modality microscopic imaging of the human carotid atherosclerotic plaques. We first show that the acoustic impedance values are statistically higher in calcified regions compared with the collagen-rich areas. We then use CdTe/CdS quantum dots for imaging the atherosclerotic plaques by TRFS and show that fluorescence lifetime values of the quantum dots in collagen-rich areas are notably different from the ones in calcified areas. In summary, both modalities are successful in differentiating the calcified regions from the collagen-rich areas within the plaques indicating that these techniques are confirmatory and may be combined to characterize atherosclerotic plaques in the future.

Bioengineered H-Ferritin Nanocages for Quantitative Imaging of Vulnerable Plaques in Atherosclerosis

Inflammation and calcification concomitantly drive atherosclerotic plaque progression and rupture and are the compelling targets for identifying plaque vulnerability. However, current imaging modalities for vulnerable atherosclerotic plaques are often limited by inadequate specificity and sensitivity. Here, we show that natural H-ferritin nanocages radiolabeled with technetium-99m (^99mTc-HFn) can identify and accurately localize macrophage-rich, atherosclerotic plaques in living mice using combined SPECT and CT. Focal ^99mTc-HFn uptake was observed in the atherosclerotic plaques with multiple high-risk features of macrophage infiltration, active calcification, positive remodeling, and necrosis on histology and in early active ongoing lesions with intense macrophage infiltration. The uptake of ^99mTc-HFn in plaques enabled quantitative measuring of the dynamic changes of inflammation during plaque progression and anti-inflammation treatment. This strategy lays the foundation of using bioengineered endogenous human ferritin nanocages for the identification of vulnerable and early active plaques as well as potential assessment of anti-inflammation therapy.

The CDK9-cyclin T1 complex mediates saturated fatty acid-induced vascular calcification by inducing expression of the transcription factor CHOP

Vascular calcification (or mineralization) is a common complication of chronic kidney disease (CKD) and is closely associated with increased mortality and morbidity rates. We recently reported that activation of the activating transcription factor 4 (ATF4) pathway through the saturated fatty acid (SFA)-induced endoplasmic reticulum (ER) stress response plays a causative role in CKD-associated vascular calcification. Here, using mouse models of CKD, we 1) studied the contribution of the proapoptotic transcription factor CCAAT enhancer-binding protein homologous protein (CHOP) to CKD-dependent medial calcification, and 2) we identified an additional regulator of ER stress-mediated CHOP expression. Transgenic mice having smooth muscle cell (SMC)-specific CHOP expression developed severe vascular apoptosis and medial calcification under CKD. Screening of a protein kinase inhibitor library identified 16 compounds, including seven cyclin-dependent kinase (CDK) inhibitors, that significantly suppressed CHOP induction during ER stress. Moreover, selective CDK9 inhibitors and CRISPR/Cas9-mediated CDK9 reduction blocked SFA-mediated induction of CHOP expression, whereas inhibitors of other CDK isoforms did not. Cyclin T1 knockout inhibited SFA-mediated induction of CHOP and mineralization, whereas deletion of cyclin T2 and cyclin K promoted CHOP expression levels and mineralization. Of note, the CDK9-cyclin T1 complex directly phosphorylated and activated ATF4. These results demonstrate that the CDK9-cyclin T1 and CDK9-cyclin T2/K complexes have opposing roles in CHOP expression and CKD-induced vascular calcification. They further reveal that the CDK9-cyclin T1 complex mediates vascular calcification through CHOP induction and phosphorylation-mediated ATF4 activation.

Coronary fluorine-18-sodium fluoride uptake is increased in healthy adults with an unfavorable cardiovascular risk profile: results from the CAMONA study

OBJECTIVE

Coronary artery fluorine-18-sodium fluoride (F-NaF) uptake reflects coronary artery calcification metabolism and is considered to be an early prognostic marker of coronary heart disease. This study evaluated the relationship between coronary artery F-NaF uptake and cardiovascular risk in healthy adults at low cardiovascular risk.

PARTICIPANTS AND METHODS

Study participants underwent blood pressure measurements, blood analyses, and coronary artery F-NaF PET/CT imaging. In addition, the 10-year risk for the development of cardiovascular disease, on the basis of the Framingham Risk Score, was estimated. Multivariable linear regression evaluated the dependence of coronary artery F-NaF uptake on cardiovascular risk factors.

RESULTS

We recruited 89 (47 men, 42 women) healthy adults aged 21-75 years. Female sex (0.34 kBq/ml; P=0.009), age (0.16 kBq/ml per SD; P=0.002), and BMI (0.42 kBq/ml per SD; P<0.001) were independent determinants of increased coronary artery F-NaF uptake (adjusted R=0.21; P<0.001). Coronary artery F-NaF uptake increased linearly according to the number of cardiovascular risk factors present (P<0.001 for a linear trend). The estimated 10-year risk for the development of cardiovascular disease was on average 2.4 times higher in adults with coronary artery F-NaF uptake in the highest quartile compared with those in the lowest quartile of the distribution (8.0 vs. 3.3%, P<0.001).

CONCLUSION

Our findings indicate that coronary artery F-NaF PET/CT imaging is feasible in healthy adults at low cardiovascular risk and that an unfavorable cardiovascular risk profile is associated with a marked increase in coronary artery F-NaF uptake.

Reference values for fluorine-18-fluorodeoxyglucose and fluorine-18-sodium fluoride uptake in human arteries: a prospective evaluation of 89 healthy adults

OBJECTIVE

Reference values of fluorine-18-fluorodeoxyglucose (F-FDG) and fluorine-18-sodium fluoride (F-NaF) uptake in human arteries are unknown. The aim of this study was to determine age-specific and sex-specific reference values of arterial F-FDG and F-NaF uptake.

PARTICIPANTS AND METHODS

Uptake of F-FDG and F-NaF was determined in the ascending aorta, aortic arch, and descending thoracic aorta. In addition, F-FDG uptake was determined in the carotid arteries and F-NaF uptake was determined in the coronary arteries. Arterial F-FDG and F-NaF uptake were quantified as the blood pool subtracted maximum activity concentration in kBq/ml (BS F-FDGmax and BS F-NaFmax, respectively). In addition to determining reference values, we evaluated the influence of age and sex on BS F-FDGmax and BS F-NaFmax.

RESULTS

Arterial F-FDG and F-NaF uptake was assessed in 89 healthy adults aged 21-75 years (mean age: 44±14 years, 53% men). Both BS F-FDGmax and BS F-NaFmax increased with age. BS F-FDGmax increased with age in the descending aorta (β=0.28; P=0.003), whereas BS F-NaFmax increased with age in the ascending aorta (β=0.18; P<0.001), aortic arch (β=0.19; P=0.006), descending aorta (β=0.33; P<0.001), and coronary arteries (β=0.20; P=0.009), respectively. BS F-FDGmax and BS F-NaFmax were not influenced by sex, except for BS F-FDGmax in the ascending aorta.

CONCLUSION

Prospective evaluation of 89 healthy adults generated age-specific and sex-specific reference values of arterial F-FDG and F-NaF uptake. Our findings indicate that arterial F-FDG and F-NaF uptake tend to increase with age.

Engineering a 3D-Bioprinted Model of Human Heart Valve Disease Using Nanoindentation-Based Biomechanics

In calcific aortic valve disease (CAVD), microcalcifications originating from nanoscale calcifying vesicles disrupt the aortic valve (AV) leaflets, which consist of three (biomechanically) distinct layers: the fibrosa, spongiosa, and ventricularis. CAVD has no pharmacotherapy and lacks in vitro models as a result of complex valvular biomechanical features surrounding resident mechanosensitive valvular interstitial cells (VICs). We measured layer-specific mechanical properties of the human AV and engineered a three-dimensional (3D)-bioprinted CAVD model that recapitulates leaflet layer biomechanics for the first time. Human AV leaflet layers were separated by microdissection, and nanoindentation determined layer-specific Young’s moduli. Methacrylated gelatin (GelMA)/methacrylated hyaluronic acid (HAMA) hydrogels were tuned to duplicate layer-specific mechanical characteristics, followed by 3D-printing with encapsulated human VICs. Hydrogels were exposed to osteogenic media (OM) to induce microcalcification, and VIC pathogenesis was assessed by near infrared or immunofluorescence microscopy. Median Young’s moduli of the AV layers were 37.1, 15.4, and 26.9 kPa (fibrosa/spongiosa/ventricularis, respectively). The fibrosa and spongiosa Young’s moduli matched the 3D 5% GelMa/1% HAMA UV-crosslinked hydrogels. OM stimulation of VIC-laden bioprinted hydrogels induced microcalcification without apoptosis. We report the first layer-specific measurements of human AV moduli and a novel 3D-bioprinted CAVD model that potentiates microcalcification by mimicking the native AV mechanical environment. This work sheds light on valvular mechanobiology and could facilitate high-throughput drug-screening in CAVD.

Intravital microscopy in the study of the tumor microenvironment: from bench to human application

Intravital microscopy (IVM) is a dynamic imaging modality that allows for the real time observation of biologic processes in vivo, including angiogenesis and immune cell interactions. In the setting of preclinical cancer models, IVM has facilitated an understanding of the tumor associated vasculature and the role of effector immune cells in the tumor microenvironment. Novel approaches to apply IVM to human malignancies have thus far focused on cancer diagnosis and tumor vessel characterization, but have the potential to provide advances in the field of personalized medicine by identifying individual patients who may respond to systemically delivered chemotherapeutic drugs or immunotherapeutic agents. In this review, we highlight the role that IVM has had in investigating tumor vasculature and the tumor microenvironment in preclinical studies and discuss its current and future applications to directly observe human tumors.

Regulation of Vascular Calcification by Growth Hormone-Releasing Hormone and Its Agonists

RATIONALE

Vascular calcification (VC) is a marker of the severity of atherosclerotic disease. Hormones play important roles in regulating calcification; estrogen and parathyroid hormones exert opposing effects, the former alleviating VC and the latter exacerbating it. To date no treatment strategies have been developed to regulate clinical VC.

OBJECTIVE

The objective of this study was to investigate the effect of growth hormone-releasing hormone (GHRH) and its agonist (GHRH-A) on the blocking of VC in a mouse model.

METHODS AND RESULTS

Young adult osteoprotegerin-deficient mice were given daily subcutaneous injections of GHRH-A (MR409) for 4 weeks. Significant reductions in calcification of the aortas of MR409-treated mice were paralleled by markedly lower alkaline phosphatase activity and a dramatic reduction in the expression of transcription factors, including the osteogenic marker gene Runx2 and its downstream factors, osteonectin and osteocalcin. The mechanism of action of GHRH-A was dissected in smooth muscle cells isolated from human and mouse aortas. Calcification of smooth muscle cells induced by osteogenic medium was inhibited in the presence of GHRH or MR409, as evidenced by reduced alkaline phosphatase activity and Runx2 expression. Inhibition of calcification by MR409 was partially reversed by MIA602, a GHRH antagonist, or a GHRH receptor-selective small interfering RNA. Treatment with MR409 induced elevated cytosolic cAMP and its target, protein kinase A which in turn blocked nicotinamide adenine dinucleotide phosphate oxidase activity and reduced production of reactive oxygen species, thus blocking the phosphorylation of nuclear factor κB (p65), a key intermediate in the ligand of receptor activator for nuclear factor-κ B-Runx2/alkaline phosphatase osteogenesis program. A protein kinase A-selective small interfering RNA or the chemical inhibitor H89 abolished these beneficial effects of MR409.

CONCLUSIONS

GHRH-A controls osteogenesis in smooth muscle cells by targeting cross talk between protein kinase A and nuclear factor κB (p65) and through the suppression of reactive oxygen species production that induces the Runx2 gene and alkaline phosphatase. Inflammation-mediated osteogenesis is thereby blocked. GHRH-A may represent a new pharmacological strategy to regulate VC.

Cell Phenotype Transitions in Cardiovascular Calcification

Cardiovascular calcification was originally considered a passive, degenerative process, however with the advance of cellular and molecular biology techniques it is now appreciated that ectopic calcification is an active biological process. Vascular calcification is the most common form of ectopic calcification, and aging as well as specific disease states such as atherosclerosis, diabetes, and genetic mutations, exhibit this pathology. In the vessels and valves, endothelial cells, smooth muscle cells, and fibroblast-like cells contribute to the formation of extracellular calcified nodules. Research suggests that these vascular cells undergo a phenotypic switch whereby they acquire osteoblast-like characteristics, however the mechanisms driving the early aspects of these cell transitions are not fully understood. Osteoblasts are true bone-forming cells and differentiate from their pluripotent precursor, the mesenchymal stem cell (MSC); vascular cells that acquire the ability to calcify share aspects of the transcriptional programs exhibited by MSCs differentiating into osteoblasts. What is unknown is whether a fully-differentiated vascular cell directly acquires the ability to calcify by the upregulation of osteogenic genes or, whether these vascular cells first de-differentiate into an MSC-like state before obtaining a “second hit” that induces them to re-differentiate down an osteogenic lineage. Addressing these questions will enable progress in preventative and regenerative medicine strategies to combat vascular calcification pathologies. In this review, we will summarize what is known about the phenotypic switching of vascular endothelial, smooth muscle, and valvular cells.

Positron emission tomography imaging of coronary atherosclerosis

Inflammation has a central role in the progression of coronary atherosclerosis. Recent developments in cardiovascular imaging with the advent of hybrid positron emission tomography have provided a window into the molecular pathophysiology underlying coronary plaque inflammation. Using novel radiotracers targeted at specific cellular pathways, the potential exists to observe inflammation, apoptosis, cellular hypoxia, microcalcification and angiogenesis in vivo. Several clinical studies are now underway assessing the ability of this hybrid imaging modality to inform about atherosclerotic disease activity and the prediction of future cardiovascular risk. A better understanding of the molecular mechanisms governing coronary atherosclerosis may be the first step toward offering patients a more stratified, personalized approach to treatment.

Inflammation and coronary artery calcification in South Asians: The Mediators of Atherosclerosis in South Asians Living in America (MASALA) study

BACKGROUND AND AIMS

Inflammatory biomarkers and adipocytokines (IBA) may contribute to atherosclerosis by promoting vascular inflammation. The association between IBA and coronary artery calcium (CAC), a marker of subclinical atherosclerosis, is not well defined in South Asians (SA). We hypothesized that IBA (high sensitivity C-reactive protein [hsCRP], tumor necrosis factor alpha [TNF-α], adiponectin, and leptin) were independently associated with and improved discrimination of CAC among SA.

METHODS

We analyzed IBA and CAC among participants in the prospective Mediators of Atherosclerosis in South Asians Living in America (MASALA) study. We used logistic regression models to examine cross-sectional associations of IBA with CAC presence (CAC >0) and severity (CAC >100), and C-statistics to assess the incremental contribution of each IBA to traditional risk factors (TRF) from the AHA/ACC Pooled Cohort Equations (PCE) for discrimination of CAC.

RESULTS

Among 906 participants in the MASALA study, women (n = 420) had significantly higher levels of hsCRP, adiponectin, and leptin but lower levels of TNF-α than men (p < .01 for all). There was no significant association between any of the four IBA and either CAC category in multivariable-adjusted models, respectively. Lastly, none of the four IBA improved discrimination of CAC presence or severity when added to elements of the PCE.

CONCLUSIONS

IBA were not associated with CAC presence or severity in the MASALA population. IBA did not help identify SA at risk of subclinical atherosclerosis, although associations with ASCVD events remain unclear. In SA, CAC may have a distinct pathophysiology independent of inflammation as measured by IBA.

Mechanisms of Arterial Calcification: The Role of Matrix Vesicles

Vascular calcification is related to vascular diseases, for example, atherosclerosis, and its comorbidities, such as diabetes and chronic kidney disease. In each condition, a distinctive histological pattern can be recognised that may influence technical choices, possible intra-operative complications, and procedure outcomes, no matter if the intervention is performed by open or endovascular means. This review considers the classification and initiating mechanisms of vascular calcification. Dystrophic and metastatic calcifications, Monckeberg's calcification, and genetic forms are firstly outlined, followed by their alleged initiation mechanisms; these include (a) ineffective macrophage efferocytosis; (b) ectopic osteogenesis driven by modified resident or circulating osteoprogenitors. As in physiological bio-mineralisation, active calcification starts with the deposition of cell derived matrix vesicles into the extracellular matrix. To substantiate this belief, an in depth ultra-structural documentation of hydroxyapatite crystal deposition on such vesicles is provided in an ex-vivo human vascular cell model. Revealing the vesicle composition and phenotype in normal and pathological vascular conditions will be essential for the development of new therapeutic strategies, in order to prevent and treat vascular calcification.

Microcalcifications, Their Genesis, Growth, and Biomechanical Stability in Fibrous Cap Rupture

For many decades, cardiovascular calcification has been considered as a passive process, accompanying atheroma progression, correlated with plaque burden, and apparently without a major role on plaque vulnerability. Clinical and pathological analyses have previously focused on the total amount of calcification (calcified area in a whole atheroma cross section) and whether more calcification means higher risk of plaque rupture or not. However, this paradigm has been changing in the last decade or so. Recent research has focused on the presence of microcalcifications (μCalcs) in the atheroma and more importantly on whether clusters of μCalcs are located in the cap of the atheroma. While the vast majority of μCalcs are found in the lipid pool or necrotic core, they are inconsequential to vulnerable plaque. Nevertheless, it has been shown that μCalcs located within the fibrous cap could be numerous and that they behave as an intensifier of the background circumferential stress in the cap. It is now known that such intensifying effect depends on the size and shape of the μCalc as well as the proximity between two or more μCalcs. If μCalcs are located in caps with very low background stress, the increase in stress concentration may not be sufficient to reach the rupture threshold. However, the presence of μCalc(s) in the cap with a background stress of about one fifth to one half the rupture threshold (a stable plaque) will produce a significant increase in local stress, which may exceed the cap rupture threshold and thus transform a non-vulnerable plaque into a vulnerable one. Also, the classic view that treats cardiovascular calcification as a passive process has been challenged, and emerging data suggest that cardiovascular calcification may encompass both passive and active processes. The passive calcification process comprises biochemical factors, specifically circulating nucleating complexes, which would lead to calcification of the atheroma. The active mechanism of atherosclerotic calcification is a cell-mediated process via cell death of macrophages and smooth muscle cells (SMCs) and/or the release of matrix vesicles by SMCs.

Plaque Calcification During Atherosclerosis Progression and Regression

Plaque calcification develops by the inflammation-dependent mechanisms involved in progression and regression of atherosclerosis. Macrophages can undergo two distinct polarization states, that is, pro-inflammatory M1 phenotype in progression and anti-inflammatory M2 phenotype in regression. In plaque progression, predominant M1 macrophages promote the initial calcium deposition within the necrotic core of the lesions, called as microcalcification, through not only vesicle-mediated mineralization as the result of apoptosis of macrophages and vascular smooth muscle cells (VSMCs), but also VSMC differentiation into early phase osteoblasts. On the other hand, in plaque regression M2 macrophages are engaged in the healing response to plaque inflammation. In association with the resolution of chronic inflammation, M2 macrophages may facilitate macroscopic calcium deposition, called as macrocalcification, through induction of osteoblastic differentiation and maturation of VSMCs. Oncostatin M, which has been shown to promote osteoblast differentiation in bone, may play a pivotal role in the development of plaque calcification. Clinically, two types of plaque calcification have distinct implications. Macrocalcification leads to plaque stability, while microcalcification is more likely to be associated with plaque rupture. Statin therapy, which reduces cardiovascular mortality, has been shown to exert its dual actions on plaque morphology, that is, regression of atheroma and increment of macroscopic calcium deposits. Statins may facilitate the healing process against plaque inflammation by enhancing M2 polarization of macrophages. Vascular calcification has pleiotropic properties as pro-inflammatory “microcalcification” and anti-inflammatory “macrocalcification”. The molecular mechanisms of this process in relation with plaque progression as well as plaque regression should be intensively elucidated.

Extracellular Vesicles As Mediators of Cardiovascular Calcification

Involvement of cell-derived extracellular particles, coined as matrix vesicles (MVs), in biological bone formation was introduced by Bonucci and Anderson in mid-1960s. In 1983, Anderson et al. observed similar structures in atherosclerotic lesion calcification using electron microscopy. Recent studies employing new technologies and high- resolution microscopy have shown that although they exhibit characteristics similar to MVs, calcifying extracellular vesicles (EVs) in cardiovascular tissues are phenotypically distinct from their bone counterparts. EVs released from cells within cardiovascular tissues may contain either inhibitors of calcification in normal physiological conditions or promoters in pathological environments. Pathological conditions characterized by mineral imbalance (e.g., atherosclerosis, chronic kidney disease, diabetes) can cause smooth muscle cells, valvular interstitial cells, and macrophages to release calcifying EVs, which contain specific mineralization-promoting cargo. These EVs can arise from either direct budding of the cell plasma membrane or through the release of exosomes from multivesicular bodies. In contrast, MVs are germinated from specific sites on osteoblast, chondrocyte, or odontoblast membranes. Much like MVs, calcifying EVs in the fibrillar collagen extracellular matrix of cardiovascular tissues serve as calcification foci, but the mineral that forms appears different between the tissues. This review highlights recent studies on mechanisms of calcifying EV formation, release, and mineralization in cardiovascular calcification. Furthermore, we address the MV–EV relationship, and offer insight into therapeutic implications to consider for potential targets for each type of mineralization.

Raman spectroscopy imaging reveals interplay between atherosclerosis and medial calcification in the human aorta

Medial calcification in the human aorta accumulates during aging and is known to be aggravated in several diseases. Atherosclerosis, another major cause of cardiovascular calcification, shares some common aggravators. However, the mechanisms of cardiovascular calcification remain poorly understood. To elucidate the relationship between medial aortic calcification and atherosclerosis, we characterized the cross-sectional distributions of the predominant minerals in aortic tissue, apatite and whitlockite, and the associated extracellular matrix. We also compared the cellular changes between atherosclerotic and nonatherosclerotic human aortic tissues. This was achieved through the development of Raman spectroscopy imaging methods that adapted algorithms to distinguish between the major biomolecules present within these tissues. We present a relationship between apatite, cholesterol, and triglyceride in atherosclerosis, with the relative amount of all molecules concurrently increased in the atherosclerotic plaque. Further, the increase in apatite was disproportionately large in relation to whitlockite in the aortic media directly underlying a plaque, indicating that apatite is more pathologically significant in atherosclerosis-aggravated medial calcification. We also discovered a reduction of β-carotene in the whole aortic intima, including a plaque in atherosclerotic aortic tissues compared to nonatherosclerotic tissues. This unprecedented biomolecular characterization of the aortic tissue furthers our understanding of pathological and physiological cardiovascular calcification events in humans.

Non-destructive two-photon excited fluorescence imaging identifies early nodules in calcific aortic-valve disease

Calcifications occur during the development of healthy bone, and at the onset of calcific aortic-valve disease (CAVD) and many other pathologies. Although the mechanisms regulating early calcium deposition are not fully understood, they may provide targets for new treatments and for early interventions. Here, we show that two-photon excited fluorescence (TPEF) can provide quantitative and sensitive readouts of calcific nodule formation, in particular in the context of CAVD. Specifically, by means of the decomposition of TPEF spectral images from excised human CAVD valves and from rat bone prior to and following demineralization, as well as from calcific nodules formed within engineered gels, we identified an endogenous fluorophore that correlates with the level of mineralization in the samples. We then developed a ratiometric imaging approach that provides a quantitative readout of the presence of mineral deposits in early calcifications. TPEF should enable non-destructive, high-resolution imaging of three-dimensional tissue specimens for the assessment of the presence of calcification.

Thrombin-Activatable Microbubbles as Potential Ultrasound Contrast Agents for the Detection of Acute Thrombosis

Acute deep vein thrombosis (DVT) is the formation of a blood clot in the deep veins of the body that can lead to fatal pulmonary embolism. Acute DVT is difficult to distinguish from chronic DVT by ultrasound (US), the imaging modality of choice, and is therefore treated aggressively with anticoagulants, which can lead to internal bleeding. Here we demonstrate that conjugating perfluorobutane-filled (PFB-filled) microbubbles (MBs) with thrombin-sensitive activatable cell-penetrating peptides (ACPPs) could lead to the development of contrast agents that detect acute thrombosis with US imaging. Successful conjugation of ACPP to PFB-filled MBs was confirmed by fluorescence microscopy and flow cytometry. Fluorescein-labeled ACPP was used to evaluate the efficiency of thrombin-triggered cleavage by measuring the mean fluorescence intensity of ACPP-labeled MBs (ACPP-MBs) before and after incubation at 37 °C with thrombin. Lastly, control MBs and ACPP-MBs were infused through a tube containing a clot, and US contrast enhancement was measured with or without the presence of a thrombin inhibitor after washing the clot with saline. With thrombin activity, 91.7 ± 14.2% of the signal was retained after ACPP-MB infusion and washing, whereas only 16.7 ± 4% of the signal was retained when infusing ACPP-MBs in the presence of hirudin, a potent thrombin inhibitor.

Aortic microcalcification is associated with elastin fragmentation in Marfan syndrome

Marfan syndrome (MFS) is a connective tissue disorder in which aortic rupture is the major cause of death. MFS patients with an aortic diameter below the advised limit for prophylactic surgery (<5 cm) may unexpectedly experience an aortic dissection or rupture, despite yearly monitoring. Hence, there is a clear need for improved prognostic markers to predict such aortic events. We hypothesize that elastin fragments play a causal role in aortic calcification in MFS, and that microcalcification serves as a marker for aortic disease severity. To address this hypothesis, we analysed MFS patient and mouse aortas. MFS patient aortic tissue showed enhanced microcalcification in areas with extensive elastic lamina fragmentation in the media. A causal relationship between medial injury and microcalcification was revealed by studies in vascular smooth muscle cells (SMCs); elastin peptides were shown to increase the activity of the calcification marker alkaline phosphatase (ALP) and reduce the expression of the calcification inhibitor matrix GLA protein in human SMCs. In murine Fbn1^C1039G/+ MFS aortic SMCs, Alpl mRNA and activity were upregulated as compared with wild-type SMCs. The elastin peptide-induced ALP activity was prevented by incubation with lactose or a neuraminidase inhibitor, which inhibit the elastin receptor complex, and a mitogen-activated protein kinase kinase-1/2 inhibitor, indicating downstream involvement of extracellular signal-regulated kinase-1/2 (ERK1/2) phosphorylation. Histological analyses in MFS mice revealed macrocalcification in the aortic root, whereas the ascending aorta contained microcalcification, as identified with the near-infrared fluorescent bisphosphonate probe OsteoSense-800. Significantly, microcalcification correlated strongly with aortic diameter, distensibility, elastin breaks, and phosphorylated ERK1/2. In conclusion, microcalcification co-localizes with aortic elastin degradation in MFS aortas of humans and mice, where elastin-derived peptides induce a calcification process in SMCs via the elastin receptor complex and ERK1/2 activation. We propose microcalcification as a novel imaging marker to monitor local elastin degradation and thus predict aortic events in MFS patients. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.