In vivo temperature heterogeneity is associated with plaque regions of increased MMP-9 activity

FURIN suppresses the progression of atherosclerosis by promoting macrophage autophagy

FURIN, a member of the mammalian proprotein convertases (PCs) family, can promote the proteolytic maturation of proproteins. It has been shown that FURIN plays an important role in the progression of atherosclerosis (AS). Current evidence indicates that autophagy widely participates in atherogenesis. This study aimed to explore whether FURIN could affect atherogenesis via autophagy. The effect of FURIN on autophagy was studied using aortic tissues from aortic dissection patients who had BENTALL surgery, as well as macrophages and ApoE-/- mice. In atherosclerotic plaques of aortic tissues from patients, FURIN expression and autophagy were elevated. In macrophages, FURIN-shRNA and FURIN-overexpression lentivirus were used to intervene in FURIN expression. The results showed that FURIN overexpression accelerated LC3 formation in macrophages during the autophagosome formation phase. Furthermore, FURIN-induced autophagy resulted in lower lipid droplet concentrations in macrophages. The western blot revealed that FURIN regulated autophagy via the AMPK/mTOR/ULK1/PI3KIII signaling pathway. In vivo, FURIN overexpression resulted in increased macrophage LC3 formation in ApoE-/- mice atherosclerotic plaques, confirming that FURIN could inhibit the progression of AS by promoting macrophage autophagy. The present study demonstrated that FURIN suppressed the progression of AS by promoting macrophage autophagy via the AMPK/mTOR/ULK1/PI3KIII signaling pathway, which attenuated atherosclerotic lesion formation. Based on this data, current findings add to our understanding of the complexity of AS.

Considerations for analysis of endothelial shear stress and strain in FSI models of atherosclerosis

Atherosclerosis is a lipid driven chronic inflammatory disease that is characterized by the formation of plaques at predilection sites. These predilection sites (side branches, curved segments, and bifurcations) have often been associated with disturbed shear stress profiles. However, in addition to shear stress, endothelial cells also experience artery wall strain that could contribute to atherosclerosis progression. Herein, we describe a method to accurately obtain these shear stress and strain profiles. We developed a fluid-structure interaction (FSI) framework for modelling arteries within a commercially available package (Abaqus, version 6.14) that included known prestresses (circumferential, axial and pressure associated). In addition, we co-registered 3D histology to a micro-CT-derived 3D reconstruction of an atherosclerotic carotid artery from a cholesterol-fed ApoE^-/- mouse to include the spatial distribution of lipids within a subject-specific model. The FSI model also incorporated a nonlinear hyperelastic material model with regionally-varying properties that distinguished between healthy vessel wall and plaque. FSI predicted a lower shear stress than CFD (~-12%), but further decreases in plaque regions with softer properties (~-24%) were dependent on the approach used to implement the prestresses in the artery wall. When implemented with our new hybrid approach (zero prestresses in regions of lipid deposition), there was significant heterogeneity in endothelial shear stress in the atherosclerotic artery due to variations in stiffness and, in turn, wall strain. In conclusion, when obtaining endothelial shear stress and strain in diseased arteries, a careful consideration of prestresses is necessary. This paper offers a way to implement them.

CD163+ macrophages are associated with a vulnerable plaque phenotype in human carotid plaques

Macrophages are a functionally heterogeneous group of immune cells abundant in atherosclerotic plaques. Macrophages expressing CD163 are associated with intraplaque hemorrhage and have previously been considered atheroprotective. However, in a recent study CD163-deficient atherosclerotic ApoE^-/- mice exhibited smaller and less complex plaques, suggesting a proatherogenic role of CD163. Previous smaller studies on CD163+ macrophages and plaque stability in humans have yielded diverging results. Here we assessed the association of CD163+ cells to plaque vulnerability in a large cohort of human carotid plaques. CD163 protein expression was analyzed by immunohistochemistry in 200 human carotid plaques removed by endarterectomy from 103 patients with and 93 patients without cerebrovascular symptoms. Furthermore, CD163 mRNA expression was analyzed in 66 of the plaques. Both protein and mRNA expression of CD163 was higher in plaques from symptomatic patients and in plaques with high vulnerability index. CD163+ macrophages were primarily found in shoulder regions and in the center of the plaques. The present data show that CD163 is associated with increased plaque vulnerability in human carotid plaques, supporting the notion that CD163+ macrophages could contribute to clinical events.

Sulfated polysaccharide from Undaria pinnatifida stabilizes the atherosclerotic plaque via enhancing the dominance of the stabilizing components

The purpose of this study was to investigate the stable effect and mechanism of sulfated polysaccharide from Undaria pinnatifida (SPUP) on atherosclerotic plaque. The results showed that atherosclerotic plaques in the ApoE-/- mice of high-fat diet model group increased significantly without drug intervention. The content of vulnerable components (lipid, inflammatory macrophage) increased significantly, and the content of stability components (smooth muscle cell, collagen) reduced significantly. However, it could find that atherosclerotic plaque areas were decreased in a dose-dependent manner after SPUP intervention. SPUP could enhance the dominance of the stability components in plaque, and reduce the content of vulnerable component. Furthermore, SPUP could significantly reduce the matrix metalloprotein-9 content in atherosclerotic plaque. These results suggested that SPUP could stabilize atherosclerotic plaque by enhancing the dominance of the stability components content, reducing the vulnerability components content, and lowering the vulnerability index value.

Characterization of Macrophage Polarization States Using Combined Measurement of 2-Deoxyglucose and Glutamine Accumulation: Implications for Imaging of Atherosclerosis

OBJECTIVE

Despite the early promising results of ¹⁸F-fluorodeoxyglucose positron emission tomography for assessment of vessel wall inflammation, its accuracy in prospective identification of vulnerable plaques has remained limited. Additionally, previous studies have indicated that ¹⁸F-fluorodeoxyglucose uptake alone may not allow for accurate identification of specific macrophage activation states. We aimed to determine whether combined measurement of glucose and glutamine accumulation-the 2 most important bioenergetic substrates for macrophages-improves the distinction of macrophage inflammatory states and can be utilized to image atherosclerosis.

APPROACH AND RESULTS

Murine peritoneal macrophages (MΦ) were activated ex vivo into proinflammatory states with either lipopolysaccharide (MΦ_LPS) or interferon-γ+tumor necrosis factor-α (MΦ_{IFN-γ+TNF-α}). An alternative polarization phenotype was induced with interleukin-4 (MΦ_IL-4). The pronounced increase in 2-deoxyglucose uptake distinguishes MΦ_LPS from MΦ_{IFN-γ+TNF-α}, MΦ_IL-4, and unstimulated macrophages (MΦ₀). Despite having comparable levels of 2-deoxyglucose accumulation, MΦ_IL-4 can be distinguished from both MΦ_{IFN-γ+TNF-α} and MΦ₀ based on the enhanced glutamine accumulation, which was associated with increased expression of a glutamine transporter, Slc1a5. Ex vivo autoradiography experiments demonstrated distinct and heterogenous patterns of ¹⁸F-fluorodeoxyglucose and ¹⁴C-glutamine accumulation in atherosclerotic lesions of low-density lipoprotein receptor-null mice fed a high-fat diet.

CONCLUSIONS

Combined assessment of glutamine and 2-deoxyglucose accumulation improves the ex vivo identification of macrophage activation states. Combined ex vivo metabolic imaging demonstrates heterogenous and distinct patterns of substrate accumulation in atherosclerotic lesions. Further studies are required to define the in vivo significance of glutamine uptake in atherosclerosis and its potential application in identification of vulnerable plaques.

Noninvasive detection of increased carotid artery temperature in patients with coronary artery disease predicts major cardiovascular events at one year: Results from a prospective multicenter study

BACKGROUND AND AIMS

Limited prospective data have been reported regarding the impact of carotid inflammation on cardiovascular events in patients with coronary artery disease (CAD). Microwave radiometry (MWR) is a noninvasive, simple method that has been used for evaluation of carotid artery temperature which, when increased, predicts 'inflamed' plaques with vulnerable characteristics. We prospectively tested the hypothesis that increased carotid artery temperature predicts future cerebro- and cardiovascular events in patients with CAD.

METHODS

Consecutive patients from 3 centers, with documented CAD by coronary angiography, were studied. In both carotid arteries, common carotid intima-media thickness and plaque thickness were evaluated by ultrasound. Temperature difference (ΔT), measured by MWR, was considered as the maximal temperature along the carotid artery minus the minimum; ΔT ≥0.90 °C was assigned as high. Major cardiovascular events (MACE, death, stroke, myocardial infarction or revascularization) were recorded during the following year.

RESULTS

In total, 250 patients were studied; of them 40 patients (16%) had high ΔT values in both carotid arteries. MACEs occurred in 30% of patients having bilateral high ΔT versus 3.8% in the remaining patients (p<0.001). Bilateral high ΔT was independently associated with increased one-year MACE rate (HR = 6.32, 95% CI 2.42-16.53, p<0.001, by multivariate cox regression hazard model). The addition of ΔT information on a baseline model based on cardiovascular risk factors and extent of CAD significantly increased the prognostic value of the model (c-statistic increase 0.744 to 0.845, pdif = 0.05) CONCLUSIONS: Carotid inflammation, detected by MWR, has an incremental prognostic value in patients with documented CAD.

ADAMTS-7 is associated with a high-risk plaque phenotype in human atherosclerosis

Several large-scale genome-wide association studies have identified single-nucleotide polymorphisms in the genomic region of A Disintegrin And Metalloproteinase with ThromboSpondin type 1 repeats (ADAMTS)-7 and associations to coronary artery disease. Experimental studies have provided evidence for a functional role of ADAMTS-7 in both injury-induced vascular neointima formation and development of atherosclerotic lesions. However, whether ADAMTS-7 is associated with a specific plaque phenotype in humans has not been investigated. Carotid plaques (n = 206) from patients with and without cerebrovascular symptoms were analyzed for expression of ADAMTS-7 by immunohistochemistry and correlated to components associated with plaque vulnerability. Plaques from symptomatic patients showed increased levels of ADAMTS-7 compared with lesions from asymptomatic patients. High levels of ADAMTS-7 correlated with high levels of CD68-staining and lipid content, but with low smooth muscle cell and collagen content, which together are characteristics of a vulnerable plaque phenotype. ADAMTS-7 levels above median were associated with increased risk for postoperative cardiovascular events. Our data show that ADAMTS-7 is associated with a vulnerable plaque phenotype in human carotid lesions. These data support previous observations of a potential proatherogenic role of ADAMTS-7.

Inducing Persistent Flow Disturbances Accelerates Atherogenesis and Promotes Thin Cap Fibroatheroma Development in D374Y-PCSK9 Hypercholesterolemic Minipigs

BACKGROUND

Although disturbed flow is thought to play a central role in the development of advanced coronary atherosclerotic plaques, no causal relationship has been established. We evaluated whether inducing disturbed flow would cause the development of advanced coronary plaques, including thin cap fibroatheroma.

METHODS AND RESULTS

D374Y-PCSK9 hypercholesterolemic minipigs (n=5) were instrumented with an intracoronary shear-modifying stent (SMS). Frequency-domain optical coherence tomography was obtained at baseline, immediately poststent, 19 weeks, and 34 weeks, and used to compute shear stress metrics of disturbed flow. At 34 weeks, plaque type was assessed within serially collected histological sections and coregistered to the distribution of each shear metric. The SMS caused a flow-limiting stenosis, and blood flow exiting the SMS caused regions of increased shear stress on the outer curvature and large regions of low and multidirectional shear stress on the inner curvature of the vessel. As a result, plaque burden was ≈3-fold higher downstream of the SMS than both upstream of the SMS and in the control artery (P<0.001). Advanced plaques were also primarily observed downstream of the SMS, in locations initially exposed to both low (P<0.002) and multidirectional (P<0.002) shear stress. Thin cap fibroatheroma regions demonstrated significantly lower shear stress that persisted over the duration of the study in comparison with other plaque types (P<0.005).

CONCLUSIONS

These data support a causal role for lowered and multidirectional shear stress in the initiation of advanced coronary atherosclerotic plaques. Persistently lowered shear stress appears to be the principal flow disturbance needed for the formation of thin cap fibroatheroma.

The activation of the cannabinoid receptor type 2 reduces neutrophilic protease-mediated vulnerability in atherosclerotic plaques

AIMS

The activation of cannabinoid receptor type 2 (CB(2))-mediated pathways might represent a promising anti-atherosclerotic treatment. Here, we investigated the expression of the endocannabinoid system in human carotid plaques and the impact of CB(2) pharmacological activation on markers of plaque vulnerability in vivo and in vitro.

METHODS AND RESULTS

The study was conducted using all available residual human carotid tissues (upstream and downstream the blood flow) from our cohort of patients symptomatic (n = 13) or asymptomatic (n = 27) for ischaemic stroke. Intraplaque levels of 2-arachidonoylglycerol, anandamide N-arachidonoylethanolamine, N-palmitoylethanolamine, N-oleoylethanolamine, and their degrading enzymes (fatty acid amide hydrolase and monoacylglycerol lipase) were not different in human plaque portions. In the majority of human samples, CB(1) (both mRNA and protein levels) was undetectable. In downstream symptomatic plaques, CB(2) protein expression was reduced when compared with asymptomatic patients. In these portions, CB(2) levels were inversely correlated (r = -0.4008, P = 0.0170) with matrix metalloprotease (MMP)-9 content and positively (r = 0.3997, P = 0.0174) with collagen. In mouse plaques, CB(2) co-localized with neutrophils and MMP-9. Treatment with the selective CB(2) agonist JWH-133 was associated with the reduction in MMP-9 content in aortic root and carotid plaques. In vitro, pre-incubation with JWH-133 reduced tumour necrosis factor (TNF)-α-mediated release of MMP-9. This effect was associated with the reduction in TNF-α-induced ERK1/2 phosphorylation in human neutrophils.

CONCLUSION

Cannabinoid receptor type 2 receptor is down-regulated in unstable human carotid plaques. Since CB(2) activation prevents neutrophil release of MMP-9 in vivo and in vitro, this treatment strategy might selectively reduce carotid vulnerability in humans.

Atherosclerosis plaque heterogeneity and response to therapy detected by in vivo molecular imaging of matrix metalloproteinase activation

Matrix metalloproteinases (MMPs) play a key role in the development of atherosclerosis and its complications. In vivo detection and quantification of MMP activation can help track the propensity to complications and response to therapy. We sought to establish an in vivo imaging approach for monitoring MMP activation in atherosclerotic mouse aorta and use it to assess the response to dietary modification.

METHOD

Apolipoprotein-deficient mice were fed normal chow or a high-fat diet (HFD) for up to 3 mo or a HFD for 2 mo, followed by 1 mo on normal chow. Then they underwent micro-SPECT/CT, along with autoradiography and oil red O staining of tissues.

RESULTS

After 3 mo of HFD, there was considerable atherosclerosis in the aorta. In vivo micro-SPECT/CT using RP782 (an (111)In-labeled tracer targeting activated MMPs) showed a heterogeneous pattern of tracer uptake along the aorta. Heterogeneity of RP782 uptake was confirmed by autoradiography, and specificity was demonstrated using excess unlabeled precursor. Tracer uptake quantified by micro-SPECT significantly correlated with uptake quantified by autoradiography. Comparison of oil red O staining with autoradiography demonstrated areas of discordance between plaque presence and tracer uptake. HFD withdrawal led to significant reduction in RP782 uptake beyond the effect on plaque area. MMP expression and macrophage infiltration were similarly heterogeneous along the aorta and significantly reduced after withdrawal from the HFD. Finally, RP782 uptake significantly correlated with aortic macrophage content.

CONCLUSION

Molecular imaging of MMP activation reveals the heterogeneity of atherosclerotic plaques and is a useful tool for tracking plaque biology and response to therapy.

Fluorescence lifetime imaging for the characterization of the biochemical composition of atherosclerotic plaques

This study investigates the ability of a flexible fiberoptic-based fluorescence lifetime imaging microscopy (FLIM) technique to resolve biochemical features in plaque fibrotic cap associated with plaque instability and based solely on fluorescence decay characteristics. Autofluorescence of atherosclerotic human aorta (11 autopsy samples) was measured at 48 locations through two filters, F377: 377∕50 and F460: 460∕60 nm (center wavelength∕bandwidth). The fluorescence decay dynamic was described by average lifetime (τ) and four Laguerre coefficients (LECs) retrieved through a Laguerre deconvolution technique. FLIM-derived parameters discriminated between four groups [elastin-rich (ER), elastin and macrophage-rich (E+M), collagen-rich (CR), and lipid-rich (LR)]. For example, τ(F377) discriminated ER from CR (R = 0.84); τ(F460) discriminated E+M from CR and ER (R = 0.60 and 0.54, respectively); LEC-1(F377) discriminated CR from LR and E+M (R = 0.69 and 0.77, respectively); P < 0.05 for all correlations. Linear discriminant analysis was used to classify this data set with specificity >87% (all cases) and sensitivity as high as 86%. Current results demonstrate for the first time that clinically relevant features (e.g., ratios of lipid versus collagen versus elastin) can be evaluated with a flexible-fiber based FLIM technique without the need for fluorescence intensity information or contrast agents.

Imaging the vulnerable plaque

Cardiovascular diseases are still the primary causes of mortality in the United States and in Western Europe. Arterial thrombosis is triggered by a ruptured atherosclerotic plaque and precipitates an acute vascular event, which is responsible for the high mortality rate. These rupture-prone plaques are called "vulnerable plaques." During the past decades, much effort has been put toward accurately detecting the presence of vulnerable plaques with different imaging techniques. In this review, we provide an overview of the currently available invasive and noninvasive imaging modalities used to detect vulnerable plaques. We will discuss the upcoming challenges in translating these techniques into clinical practice and in assigning them their exact place in the decision-making process.

Genetic polymorphism c.1562C>T of the MMP-9 is associated with macroangiopathy in type 2 diabetes mellitus

OBJECTIVE

To determine whether the matrix metalloproteinase-9 (MMP-9) c.1562C>T polymorphism has an effect on the plasma MMP-9 levels and the macroangiopathic complications in type 2 diabetes mellitus (T2DM).

METHODS

The genotypes and allelic frequencies of the MMP-9 c.1562C>T were examined with polymerase chain reaction and restriction fragment length polymorphism in 320 patients with T2DM and 160 unrelated healthy subjects. The plasma concentrations of MMP-9 were determined in all subjects.

RESULTS

The mean plasma concentrations of MMP-9 of patients with T2DM were significantly higher than that of controls and the plasma levels of MMP-9 were higher in diabetic patients with macroangiopathy than in patients without macroangiopathy (P<0.05). The genotype (CC, CT, and TT) distribution of c.1562C>T polymorphism of the MMP-9 gene was 60.0%, 31.3%, and 8.8% in diabetic patients with macroangiopathy, 76.3%, 21.3%, and 2.5% in patients without macroangiopathy, and 77.5%, 21.3%, 1.3% in controls, respectively, a significant difference was found between diabetic patients with and without macroangiopathy (P<0.05). The frequency of the allele T was higher in patients with macroangiopathy than in patients without macroangiopathy (24.4% vs 13.1%; P<0.05). Moreover, the plasma MMP-9 levels were markedly higher in patients with TT genotype than those with CC or CT genotype in patients with macroangiopathy (P<0.05).

CONCLUSION

The MMP-9 c.1562C>T gene polymorphism associated with a predisposition to increased plasma MMP-9 levels could constitute a useful predictive marker for diabetic macroangiopathy.

Correlation between morphologic characteristics and local temperature differences in culprit lesions of patients with symptomatic coronary artery disease

OBJECTIVES

The purpose of this study was to investigate the possible correlation between morphologic and functional characteristics of culprit lesions (CL) in patients with acute coronary syndromes (ACS) and chronic stable angina (CSA).

BACKGROUND

Intravascular ultrasound (IVUS) provides morphologic assessment and intracoronary thermography (ICT) evaluates the local inflammatory activation of CL.

METHODS

Eighty-one consecutive patients, 48 with ACS and 33 with CSA, were enrolled. Ratio of lesion to reference external elastic membrane area, indicated by IVUS, was defined as positive remodeling index (pRi) (> or =1) or negative remodeling index (nRi) (<1). We also investigated the existence of ruptured plaque (rp) in the CL. By ICT temperature difference (DeltaT) between the CL and the proximal vessel wall was measured.

RESULTS

Patients with ACS had greater remodeling index than patients with CSA (1.15 +/- 0.18 vs. 0.90 +/- 0.12; p < 0.01), as well as increased DeltaT (0.08 +/- 0.03 degrees C vs. 0.04 +/- 0.02 degrees C; p < 0.01). Patients with pRi had higher DeltaT than patients with nRi (0.07 +/- 0.03 degrees C vs. 0.04 +/- 0.02 degrees C; p < 0.001). In patients with nRi there was no difference in DeltaT between ACS and CSA (p = 0.22). Patients with rp had increased DeltaT compared with patients without rp (0.09 +/- 0.03 degrees C vs. 0.05 +/- 0.02 degrees C; p < 0.01). Multivariate analysis showed that DeltaT was independently correlated with the presence of rp, pRi, and ACS.

CONCLUSIONS

The present study showed that culprit lesions with plaque rupture and positive arterial remodeling have increased thermal heterogeneity, although in certain patients a discrepancy between morphogic and functional characteristics was observed. A combination of morphologic and functional examination may offer additional diagnostic and prognostic information.

In vivo plaque characterization using intravascular ultrasound-virtual histology in a porcine model of complex coronary lesions

OBJECTIVE

To determine the accuracy of detection of different tissue types of intravascular ultrasound-virtual histology (IVUS-VH) in a porcine model of complex coronary lesions.

METHODS AND RESULTS

Coronary lesions were induced by injecting liposomes containing human oxidized low-density lipoprotein into the adventitia of the arteries. IVUS-VH imaging was performed in vivo at 8.2+/-1.6 weeks after injection. A total of 60 vascular lesions were analyzed and compared with their correspondent IVUS-VH images. Correlation analysis was performed using linear regression models. Compared with histology, IVUS-VH correctly identified the presence of fibrous, fibro-fatty, and necrotic tissue in 58.33%, 38.33%, and 38.33% of lesions, respectively. The sensitivity of IVUS-VH for the detection of fibrous, fibro-fatty, and necrotic core tissue was 76.1%, 46%, and 41.1% respectively. A linear regression analysis performed for each individual plaque component did not show strong correlation that would allow significant prediction of individual values.

CONCLUSIONS

In a porcine model of complex coronary lesions, IVUS-VH was not accurate in detecting the relative amount of specific plaque components within each individual corresponding histological specimen.

A numerical study on the influence of vulnerable plaque composition on intravascular thermography measurements

Intracoronary thermography is a technique that measures lumen wall temperatures for vulnerable plaque detection. In this paper the influence of vulnerable plaque composition on lumen wall temperatures was studied numerically. Concerning the vulnerable plaque heat generation, the location of the heat source and its heat production were varied. Concerning the heat transfer, the thermal properties of the lipid core and the location of the vasa vasorum were studied. The heat source location was the main determinant of the lumen wall temperature distribution. The strongest effect was noted when the heat producing macrophages were located in the shoulder region leading to focal spots of higher temperature. The maximal lumen wall temperature was mainly determined by the heat production of the macrophages and the cooling effect of blood. The insulating properties of the lipid core increased lumen wall temperatures when the heat source was located in the cap and the presence of vasa vasorum lowered the temperatures. These results show that the lumen wall temperature distribution is influenced by vulnerable plaque composition and that intracoronary thermography techniques require a high spatial resolution. To be able to couple temperature measurements to plaque vulnerability, intracoronary thermography needs to be combined with an imaging modality.

Development and validation of novel imaging technologies to assist translational studies in atherosclerosis

In the past decade, significant progress has been made to visualize atherosclerotic disease. Until recently, imaging technologies mainly focused on lumen and vessel wall visualization. Current advances and knowledge on the molecular mechanisms of initiation and progression of atherosclerosis has emphasized the need for imaging technologies and probes that can image function and biology rather than anatomy. This field of molecular imaging is now in rapid development with new imaging agents that aim at visualizing processes involved in atherosclerosis such as inflammation, macrophage activation, protease activity, angiogenesis, apoptosis, lipid accumulation and thrombus formation.: