Association of high-density lipoprotein levels and carotid atherosclerotic plaque characteristics by magnetic resonance imaging

Combined spatiotemporal and frequency-dependent shear wave elastography enables detection of vulnerable carotid plaques as validated by MRI

Fatal cerebrovascular events are often caused by rupture of atherosclerotic plaques. However, rupture-prone plaques are often distinguished by their internal composition rather than degree of luminal narrowing, and conventional imaging techniques might thus fail to detect such culprit lesions. In this feasibility study, we investigate the potential of ultrasound shear wave elastography (SWE) to detect vulnerable carotid plaques, evaluating group velocity and frequency-dependent phase velocities as novel biomarkers for plaque vulnerability. In total, 27 carotid plaques from 20 patients were scanned by ultrasound SWE and magnetic resonance imaging (MRI). SWE output was quantified as group velocity and frequency-dependent phase velocities, respectively, with results correlated to intraplaque constituents identified by MRI. Overall, vulnerable lesions graded as American Heart Association (AHA) type VI showed significantly higher group and phase velocity compared to any other AHA type. A selection of correlations with intraplaque components could also be identified with group and phase velocity (lipid-rich necrotic core content, fibrous cap structure, intraplaque hemorrhage), complementing the clinical lesion classification. In conclusion, we demonstrate the ability to detect vulnerable carotid plaques using combined SWE, with group velocity and frequency-dependent phase velocity providing potentially complementary information on plaque characteristics. With such, the method represents a promising non-invasive approach for refined atherosclerotic risk prediction.

HDL-C, ApoA1 and VLDL-TG as biomarkers for the carotid plaque presence in patients with metabolic syndrome

AIM

Hypercholesterolemia and hyper LDL-C are associated with the atherosclerosis (AS). The current study was performed to evaluate the implication of the others lipoproteins (HDL, LDL, VLDL) and apolipoproteins (ApoA1, ApoB100) with subclinical atherosclerosis (carotid plaque) in patients with metabolic syndrome (MetS) free from cardiovascular disease (CVD).

METHODS

Prospective transversal study was conducted in patients with MetS free from cardiovascular disease (CVD). The lipids, lipoproteins and apolipoproteins were measured. The lipoproteins (HDL, LDL, VLDL) were obtained by the precipitation method. The carotid plaque (CP) was evaluated by ultrasonography, method for assessing AS. Logistic regression and analysis tree were used to look for the association and the incrimination of the lipoproteins with the presence of CP.

RESULTS

The CP incidence was 60% among the participants, 34.29% on the right and the left plaque against 25.71% for only one plaque. The HDL-C was the only lipoprotein associated with the CP after adjustment of the age, the sex and BMI (OR: 0.007 P: 0.046) with the logistic regression analysis, HDL-C (<0.35 g/l), ApoA1 (<1.43 g/l) and VLDL-TG (>0.656 g/l) are implicated in the presence of CP with the analysis tree analysis.

CONCLUSION

Lower level of HDL-C is associated with CP, HDL-C, ApoA1, and high level VLDL-TG but not total cholesterol, and LDL-Care useful parameters in the assessment of initial atherosclerosis in metabolic syndrome.

A Shift in ApoM/S1P Between HDL-Particles in Women With Type 1 Diabetes Mellitus Is Associated With Impaired Anti-Inflammatory Effects of the ApoM/S1P Complex

Objective—

Type 1 diabetes mellitus (T1D) patients have an increased risk of cardiovascular disease despite high levels of high-density lipoproteins (HDL). Apolipoprotein M (apoM) and its ligand sphingosine 1-phospate (S1P) exert many of the anti-inflammatory effects of HDL. We investigated whether apoM and S1P are altered in T1D and whether apoM and S1P are important for HDL functionality in T1D.

Approach and Results—

ApoM and S1P were quantified in plasma from 42 healthy controls and 89 T1D patients. HDL was isolated from plasma and separated into dense, medium-dense, and light HDL by ultracentrifugation. Primary human aortic endothelial cells were challenged with tumor necrosis factor-α in the presence or absence of isolated HDL. Proinflammatory adhesion molecules E-selectin and vascular cellular adhesion molecule-1 were quantified by flow cytometry. Activation of the S1P 1 - receptor was evaluated by analyzing downstream signaling targets and receptor internalization. There were no differences in plasma levels of apoM and S1P between controls and T1D patients, but the apoM/S1P complexes were shifted from dense to light HDL particles in T1D. ApoM/S1P in light HDL particles from women were less efficient in inhibiting expression of vascular cellular adhesion molecule-1 than apoM/S1P in denser particles. The light HDL particles were unable to activate Akt, whereas all HDL subfractions were equally efficient in activating Erk and receptor internalization.

Conclusions—

ApoM/S1P in light HDL particles were inefficient in inhibiting tumor necrosis factor-α–induced vascular cellular adhesion molecule-1 expression in contrast to apoM/S1P in denser HDL particles. T1D patients have a higher proportion of light particles and hence more dysfunctional HDL, which could contribute to the increased cardiovascular disease risk associated with T1D.

Ultrasound-Based Carotid Elastography for Detection of Vulnerable Atherosclerotic Plaques Validated by Magnetic Resonance Imaging

Ultrasound-based carotid elastography has been developed to estimate the mechanical properties of atherosclerotic plaques. The objective of this study was to evaluate the in vivo capability of carotid elastography in vulnerable plaque detection using high-resolution magnetic resonance imaging as reference. Ultrasound radiofrequency data of 46 carotid plaques from 29 patients (74 ± 5 y old) were acquired and inter-frame axial strain was estimated with an optical flow method. The maximum value of absolute strain rate for each plaque was derived as an indicator for plaque classification. Magnetic resonance imaging of carotid arteries was performed on the same patients to classify the plaques into stable and vulnerable groups for carotid elastography validation. The maximum value of absolute strain rate was found to be significantly higher in vulnerable plaques (2.15 ± 0.79 s(-1), n = 27) than in stable plaques (1.21 ± 0.37 s(-1), n = 19) (p < 0.0001). Receiver operating characteristic curve analysis was performed, and the area under the curve was 0.848. Therefore, the in vivo capability of carotid elastography to detect vulnerable plaques, validated by magnetic resonance imaging, was proven, revealing the potential of carotid elastography as an important tool in atherosclerosis assessment and stroke prevention.

Analysis of Multicontrast Carotid Plaque MR Imaging

Plaque imaging by MR imaging provides a wealth of information on the characteristics of individual plaque that may reveal vulnerability to rupture, likelihood of progression, or optimal treatment strategy. T1-weighted and T2-weighted images among other options reveal plaque morphology and composition. Dynamic contrast-enhanced-MR imaging reveals plaque activity. To extract this information, image processing tools are needed. Numerous approaches for analyzing such images have been developed, validated against histologic gold standards, and used in clinical studies. These efforts are summarized in this article.

Clinical factors associated with high-risk carotid plaque features as assessed by magnetic resonance imaging in patients with established vascular disease (from the AIM-HIGH Study)

Association between clinical factors and high-risk plaque features, such as, thin or ruptured cap, intraplaque hemorrhage, presence of lipid-rich necrotic core (LRNC), and increased LRNC volume as assessed by magnetic resonance imaging (MRI), was examined in patients with established vascular disease in the Atherothrombosis Intervention in Metabolic Syndrome With Low HDL/High Triglycerides (AIM-HIGH) trial. A total of 214 subjects underwent carotid MRI and had acceptable image quality for assessment of plaque burden, tissue contents, and MRI-modified American Heart Association lesion type by a core laboratory. We found that 77% of subjects had carotid plaques, 52% had lipid-containing plaques, and 11% had advanced American Heart Association type-VI lesions with possible surface defect, intraplaque hemorrhage, or mural thrombus. Type-VI lesions were associated with older age (odds ratio [OR] = 2.6 per 5 years increase, p <0.001). After adjusting for age, these lesions were associated with history of cerebrovascular disease (OR = 4.1, p = 0.01), higher levels of lipoprotein(a) (OR = 2.0 per 1 SD increase, p = 0.02), and larger percent wall volume (PWV [OR = 4.6 per 1 SD increase, p <0.001]) but, were negatively associated with metabolic syndrome (OR = 0.2, p = 0.02). Presence of LRNC was associated with the male gender (OR = 3.2, p = 0.02) and PWV (OR = 3.8 per 1 SD, p <0.001); however, it was negatively associated with diabetes (OR = 0.4, p = 0.02) and high-density lipoprotein cholesterol levels (OR = 0.7 per 1 SD, p = 0.02). Increased percent LRNC was associated with PWV (regression coefficient = 0.36, p <0.001) and negatively associated with ApoA1 levels (regression coefficient = -0.20, p = 0.03). In conclusion, older age, male gender, history of cerebrovascular disease, larger plaque burden, higher lipoprotein(a), and lower high-density lipoprotein cholesterol or ApoA1 level have statistically significant associations with high-risk plaque features. Metabolic syndrome and diabetes showed negative associations in this population.

High-density lipoprotein subfractions and carotid plaque: the Northern Manhattan Study

OBJECTIVE

The objective of this cross-sectional analysis was to investigate the relation between two major high-density lipoprotein cholesterol (HDL-C) subfractions (HDL2-C and HDL3-C) and carotid plaque in a population based cohort.

METHODS

We evaluated 988 stroke-free participants (mean age 66 ± 8 years; 40% men; 66% Hispanic and 34% Non-Hispanic) with available data on HDL subfractions using precipitation method and carotid plaque area and thickness assessed by a high-resolution 2D ultrasound. The associations between HDL-C subfractions and plaque measurements were analyzed by quantile regression.

RESULTS

Plaque was present in 56% of the study population. Among those with plaque, the mean ± SD plaque area was 19.40 ± 20.46 mm² and thickness 2.30 ± 4.45 mm. The mean ± SD total HDL-C was 46 ± 14 mg/dl, HDL2-C 14 ± 8 mg/dl, and HDL3-C 32 ± 8 mg/dl. After adjusting for demographics and vascular risk factors, there was an inverse association between HDL3-C and plaque area (per mg/dl: beta = -0.26 at the 75th percentile, p = 0.001 and beta = -0.32 at the 90th percentile, p = 0.02). A positive association was observed between HDL2-C and plaque thickness (per mg/dl; beta = 0.02 at the 90% percentile, p = 0.003). HDL-C was associated with plaque area (per mg/dl: beta = -0.18 at the 90th percentile, p = 0.01), but only among Hispanics.

CONCLUSION

In our cohort we observed an inverse association between HDL3-C and plaque area and a positive association between HDL2-C and plaque thickness. HDL-C subfractions may have different contributions to the risk of vascular disease. More studies are needed to fully elucidate HDL-C anti-atherosclerotic functions in order to improve HDL-based treatments in prevention of vascular disease and stroke.

Molecular Magnetic Resonance Imaging for the Detection of Vulnerable Plaques: Is It Possible?: Retracted

Recent advances in molecular resonance imaging of atherosclerosis enable to visualize atherosclerotic plaques in vivo using molecular targeted contrast agents. This offers opportunities to study atherosclerosis development and plaque vulnerability noninvasively. In this review, we discuss MRI contrast agents targeted toward atherosclerotic plaques and illustrate how these new imaging platforms could assist in our understanding of atherogenesis and atheroprogression. In particular, we highlight the challenges and limitations of the different contrast agents and hurdles for clinical application. We describe the most promising existing compounds to detect atherosclerosis and plaque vulnerability. Of particular interest are the fibrin-targeted compounds that detect thrombi and, furthermore, the contrast agents targeted to integrins that allow to visualize plaque neovascularization. Moreover, vascular cell adhesion molecule 1-targeted iron oxides seem promising for early detection of atherosclerosis. These targeted MRI contrast agents, however promising and well characterized in (pre)clinical models, lack specificity for plaque vulnerability.

Utilizing imaging tools in lipidology: examining the potential of MRI for monitoring cholesterol therapy

Lipid abnormalities play important roles in the development of atherosclerosis. Lipid therapies result in alterations in atherosclerotic plaques including halting of progression of the plaque, lipid transport out of the plaque and reducing inflammatory activity, which lead to plaque morphologies that are less prone to disruption, the main cause of clinical events. In order to investigate and monitor plaque morphological changes during lipid therapy in vivo we need an imaging method that can provide accurate assessment of plaque tissue components and activity. MRI of atherosclerosis has been validated as a reliable assessment of the size of the vessel lumen, but also the size of the plaque, its tissue composition and plaque activity, including inflammation. The purpose of this review is to summarize the state of evidence for the direct assessment of atherosclerotic plaque and its change by MRI, and to establish the proven role of MRI of atherosclerosis in pharmaceutical trials with lipid therapy.

Nicotinic acid has anti-atherogenic and anti-inflammatory properties on advanced atherosclerotic lesions independent of its lipid-modifying capabilities

Inflammation contributes to atherosclerotic plaque initiation and progression. Recent studies suggest that nicotinic acid has anti-inflammatory effects independent of its lipid-modifying capabilities. We assessed the hypothesis that administration of nicotinic acid to older apolipoprotein E (apoE)-deficient mice with established lesions will reduce lesion size and plaque inflammation independent of its lipid-modifying effects. Therefore nicotinic acid was administered to 27-week-old apo E-deficient mice exhibiting advanced atherosclerotic lesions within the innominate artery. After 27 weeks of treatment both animal groups had no significant changes in plasma lipid levels. Mice treated with nicotinic acid (n = 22) demonstrated a 30% reduction in total lesion area compared with controls (n = 20). Furthermore, they revealed a more stable plaque composition with an increase in fibrous cap thickness and a reduction in the size of the necrotic core. Immunohistochemistry demonstrated a reduced accumulation of macrophages and a reduced expression of vascular cell adhesion molecule-1 and tissue factor. Additionally, administration of nicotinic acid significantly reduced tumor necrosis factor alpha expression in the thoracic aorta as demonstrated by real-time PCR. In conclusion, these data suggest that long-term administration of nicotinic acid has anti-atherogenic and anti-inflammatory properties on advanced atherosclerotic lesions, which are independent of its lipid-modifying actions.

LDL-C/HDL-C Ratio Predicts Carotid Intima-Media Thickness Progression Better Than HDL-C or LDL-C Alone

High-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) are strong predictors of atherosclerosis. Statin-induced changes in the ratio of LDL-C to HDL-C (LDL-C/HDL-C) predicted atherosclerosis progression better than LDL-C or HDL-C alone. However, the best predictor of subclinical atherosclerosis remains unknown. Our objective was to investigate this issue by measuring changes in carotid intima-media thickness (IMT). A total of 1,920 subjects received health examinations in 1999, and were followed up in 2007. Changes in IMT (follow-up IMT/baseline IMT × 100) were measured by ultrasonography. Our results showed that changes in IMT after eight years were significantly related to HDL-C (inversely, P < 0.05) and to LDL-C/HDL-C ratio (P < 0.05). When the LDL-C/HDL-C ratios were divided into quartiles, analysis of covariance showed that increases in the ratio were related to IMT progression (P < 0.05). This prospective study demonstrated the LDL-C/HDL-C ratio is a better predictor of IMT progression than HDL-C or LDL-C alone.

Nanoparticles as magnetic resonance imaging contrast agents for vascular and cardiac diseases

Advances in nanoparticle contrast agents for molecular imaging have made magnetic resonance imaging a promising modality for noninvasive visualization and assessment of vascular and cardiac disease processes. This review provides a description of the various nanoparticles exploited for imaging cardiovascular targets. Nanoparticle probes detecting inflammation, apoptosis, extracellular matrix, and angiogenesis may provide tools for assessing the risk of progressive vascular dysfunction and heart failure. The utility of nanoparticles as multimodal probes and/or theranostic agents has also been investigated. Although clinical application of these nanoparticles is largely unexplored, the potential for enhancing disease diagnosis and treatment is considerable.

Low-density lipoprotein cholesterol to high-density lipoprotein cholesterol ratio as a useful marker for early-stage carotid atherosclerosis

A higher ratio of low-density lipoprotein cholesterol (LDL-C) to high-density lipoprotein cholesterol (HDL-C) is associated with a greater risk of cardiovascular events in patients with coronary heart disease. However, the role of this lipid index during early-stage atherosclerosis has not yet been established. This study investigated relationships between LDL-C/HDL-C ratio and carotid plaque score as assessed by ultrasonography in 825 subjects from the general population (527 men, 298 women; mean age, 60.5 years). To identify factors strongly associated with plaque score, stepwise multiple regression analysis was performed using various clinical variables including conventional lipid indices. In both sexes, increased LDL-C/HDL-C ratio was associated with increased plaque score (men: beta = 0.132, P = .001; women: beta = 0.150, P = .012). This association was maintained in men with normal LDL-C level (<140 mg/dL). The highest quartile of LDL-C/HDL-C ratio (>2.9 in men, >2.6 in women) showed significantly increased plaque score even when adjusted by factors included in the final model of stepwise analysis (P = .007 in men, P = .033 in women). No association was seen between LDL-C and plaque score in the multivariate-adjusted model. These findings indicate that increased LDL-C/HDL-C ratio may also be associated with initiation of atherosclerosis. Assessment of this lipid ratio may thus facilitate early management of atherosclerotic risks better rather than assessment of LDL-C alone.

Effect of niacin ER/lovastatin on claudication symptoms in patients with peripheral artery disease

In patients with peripheral artery disease (PAD), statins may improve the symptoms of claudication. The Intermittent Claudication Proof of Principle (ICPOP) study tested the hypothesis that the combination of extended release niacin plus lovastatin would improve exercise performance in patients with PAD and claudication compared with a diet intervention. A phase 3 double-blind, parallel-group, multi-center, 28-week multi-national study evaluated subjects with a history of claudication who had an ankle—brachial index (ABI) ≤ 0.90, a reproducible peak treadmill walking time (PWT) of 1—20 minutes, and a low-density lipoprotein (LDL)-cholesterol level < 160 mg/dl (< 4.1 mmol/l). Subjects were randomly assigned to low-dose niacin 1000 mg plus lovastatin 40 mg (low niacin—statin), high-dose niacin 2000 mg plus lovastatin 40 mg (high niacin—statin), or diet intervention (diet). The co-primary efficacy endpoint of percent change in PWT and claudication onset time (COT) at 28 weeks was assessed using a graded treadmill protocol. At completion, 385 subjects were analyzed for safety and 370 subjects were analyzed for efficacy. The primary efficacy analysis showed no statistical significance for overall treatment effect at week 28 for the co-primary endpoint of PWT and COT. The PWT component of the primary endpoint increased 26.5% on diet, 37.8% on high niacin—statin ( p = 0.137) and 38.6% on low niacin—statin ( p = 0.096). Flushing as the most common event leading to discontinuation and treatment was associated with increases in liver enzymes, fasting blood glucose concentration and a decrease in platelet count.

Sphingosine-1-phosphate as a mediator of high-density lipoprotein effects in cardiovascular protection

Sphingosine-1-phosphate (S1P) has gained special attention in the high-density lipoprotein (HDL) field because HDL is the most prominent plasma carrier of S1P and because the S1P content of HDL may be responsible for many of the pleiotropic functions of HDL. This revelation has come from the evidence that HDL employ S1P receptors and signalling pathways to implement several HDL-ascribed biological effects as diverse as endothelial nitric oxide production, vasodilation, survival, and cardioprotection. This review focuses on HDL effects that are completely or partially mediated by the S1P content of the HDL particle and differentiates them from genuine HDL effects that are S1P-independent. In addition, the functional properties of 'free', HDL-unbound S1P are sometimes different from or even contrary to those of HDL-associated S1P. The nature of the physical interactions between HDL and local and systemic S1P production will be discussed as well as their consequences for organ function. Finally, we will elucidate the potential benefits and limitations of S1P analogues as a new class of functional HDL mimetics for cardiovascular therapy.

Quantitative segmentation of principal carotid atherosclerotic lesion components by feature space analysis based on multicontrast MRI at 1.5 T

The purpose of this paper is to evaluate the capability of feature space analysis (FSA) for quantifying the relative volumes of principal components (thrombus, calcification, fibrous, normal intima, and lipid) of atherosclerotic plaque tissue in multicontrast magnetic resonance images (mc-MRI) acquired in a setup resembling clinical conditions ex vivo. Utilizing endogenous contrast, proton density, T1-weighted, and T2-weighted images were acquired for 13 carotid endarterectomy (CEA) tissues under near-clinical conditions (human 1.5 T GE Excite scanner with sequence parameters comparable to an in vivo acquisition). An FSA algorithm was utilized to segment and quantify the principal components of atherosclerotic plaques. Pilot in vivo mc-MRI images were analyzed in the same way as the ex vivo images for exploring the possible adaptation of this technique to in vivo imaging. Relative abundance of principal plaque components in CEA tissues as determined by mc-MRI/FSA were compared to those measured by histology. Mean differences +/- standard deviations were 5.8 +/- 4.1% for thrombus, 1.5 +/-1.4 % for calcification, 4.0 +/-2.8% for fibrous, 8.2 +/- 10% for normal intima, and 2.4 +/- 2.2% for lipid. Reasonable quantitative agreement between the classification results obtained with FSA and histological data was obtained for near-clinical imaging conditions. Combination of mc-MRI and FSA may have an application for determining atherosclerotic lesion composition and monitoring treatment in vivo.

Therapies to increase high-density lipoprotein cholesterol and their effect on cardiovascular outcomes and regression of atherosclerosis

Epidemiological studies have shown that decreased level of high-density lipoprotein (HDL) cholesterol (C) is an independent inverse predictor of coronary artery disease (CAD) even in patients with normal levels of low-density lipoprotein (LDL)-C. There is an abundance of evidence in favor of statins and aggressive LDL-C lowering therapy for both primary and secondary prevention of CAD. In contrast, the evidence for reduction of CAD risk with HDL-C raising therapy is relatively thin, partly due to the paucity of effective and safe drugs for increasing HDL-C level. However, there are emerging new therapies for raising HDL-C level and growing evidence in favor of pharmacologic therapies to raise HDL-C level. We present in this article a review of pharmacologic therapies that are currently available to increase HDL-C level, their safety and efficacy in relation to cardiovascular endpoints.