The role of periadventitial fat in atherosclerosis

Epicardial adipose tissue volume and coronary artery calcium to predict myocardial ischemia on positron emission tomography-computed tomography studies

BACKGROUND

There appears to be an association of epicardial adipose tissue (EAT) with coronary artery disease (CAD) and its risk factors. EAT is assumed to influence CAD development by altering vasomotor tone and via toxic paracrine effects. The relationship of EAT to myocardial perfusion has not been studied.

METHODS

Quantification of EAT and CAC was performed on positron emission tomography/computed tomography (PET/CT) studies in 45 subjects (77% intermediate pre-test probability of CAD) with mild-moderate myocardial ischemia (5-14% perfusion defect, n = 23), severe ischemia (≥15% defect, n = 22) and a control group with no ischemia matched for CAD risk factors (n = 52).

RESULTS

EAT volume showed a better correlation with myocardial ischemia than total CAC (r = .47 vs r = .28, P < .01). EAT volume increased significantly from the control group to subjects with mild-moderate and severe ischemia (96.9, 124.5, and 143.9 cm(3), P < .01 for both ischemia groups vs controls). Total mean CAC was significantly higher in the severe ischemia group (676.3) than in control group (229.4) (P < .01). Multivariable logistic regression analyses showed that EAT volume was, but CAC was not, a significant predictor of ischemia after adjustment for age, sex, body mass index, and each other. EAT volume was a better predictor of ischemia than total CAC [area under the curve (AUC): .764 vs .6291, P = .04]. The combination of EAT + CAC (AUC = .7694) did not improve over EAT volume alone (P = .57).

CONCLUSIONS

In this study, EAT volume assessed by CT was an independent predictor of ischemia on PET, and outperformed CAC score in a CAD naïve population at intermediate pre-test probability of disease.

Detection of lipid in atherosclerotic vessels using ultrasound-guided spectroscopic intravascular photoacoustic imaging

Lipid is a common constituent in atherosclerotic plaques. The location and area of the lipid region is closely related to the progression of the disease. Intravascular photoacoustic (IVPA) imaging, a minimally invasive imaging modality, can spatially resolve the optical absorption property of arterial tissue. Based on the distinct optical absorption spectrum of fat in the near infrared wavelength range, spectroscopic IVPA imaging may distinguish lipid from other water-based tissue types in the atherosclerotic artery. In this study, a bench-top spectroscopic IVPA imaging system was used to ex-vivo image both atherosclerotic and normal rabbit aortas. By combing the spectroscopic IVPA image with the intravascular ultrasound (IVUS) image, lipid regions in the aorta were identified. The results demonstrated that IVUS-guided spectroscopic IVPA imaging is a promising tool to differentiate lipid in atherosclerosis.

Adipokines in periaortic and epicardial adipose tissue: differential expression and relation to atherosclerosis

AIM

Adipokines are protein products of adipose tissue with paracrine and endocrine actions, which have been implicated in the pathogenesis of cardiovascular disease. Locally produced adipokines, especially by periadventitial adipose tissue, may affect vascular physiology and pathology. We investigated the expression of adiponectin, visfatin, leptin and novel adipokines chemerin and vaspin in human periaortic and epicardial adipose tissue, as well as their correlation to aortic and coronary atherosclerosis.

METHODS

Standard immunohistochemical staining for the adipokines was performed on samples of human periaortic, pericoronary and apical epicardial adipose tissue. Atherosclerotic lesions of the adjacent vascular wall were assessed using the AHA classification.

RESULTS

Adipokines were expressed in periadventitial and apical epicardial adipose tissue and - except for adiponectin - in vascular smooth muscle cells and foam cells in atherosclerotic lesions. Aortic atherosclerosis was positively correlated with chemerin, vaspin, visfatin and leptin periaortic fat expression. Coronary atherosclerosis was positively correlated with chemerin and visfatin pericoronary fat expression. Adipose tissue adiponectin expression was negatively correlated to atherosclerosis in both locations. Expression of adipokines in apical epicardial fat was not associated with atherosclerosis.

CONCLUSIONS

Our results show: a) a different expression pattern of adiponectin, visfatin, leptin, chemerin and vaspin in periaortic, pericoronary and apical epicardial adipose tissue, b) a correlation of these adipokines with either aortic or coronary atherosclerosis or both in a pattern characteristic for each adipokine and suggest that locally produced adipokines might differently affect the atherosclerotic process in different locations.

Association of pericardial fat accumulation rather than abdominal obesity with coronary atherosclerotic plaque formation in patients with suspected coronary artery disease

OBJECTIVES

The purpose of this study was to examine the association of pericardial fat with the presence of coronary plaques.

BACKGROUND

Waist circumference, reflecting abdominal obesity, is a risk factor of metabolic syndrome and coronary artery disease (CAD). Adipose tissue secretes many factors implicated in atherogenesis, however, the role of pericardial fat (ectopic visceral fat around coronary arteries) in the pathogenesis of CAD is not clear.

METHODS

We measured total pericardial fat volume (PFV) and determined presence and characteristics of coronary plaques using 64-slice computed tomography in 171 consecutive patients suspected of CAD (101 men; mean age, 66+/-11 years, +/-SD).

RESULTS

PFV correlated with age (p<0.05), body mass index (p<0.05), waist circumference (p<0.01), and high-density lipoprotein cholesterol (p<0.01) by multivariate regression analysis. PFV was significantly larger in patients with coronary plaques, even nonstenotic or noncalcified ones, than those without plaques (any plaques, n=123; 201+/-71cm(3), nonstenotic plaques, n=51; 192+/-63, noncalcified plaques, n=32; 196+/-56 vs. no plaque, n=48; 144+/-45, p<0.001, respectively). Multivariate backward logistic regression analysis demonstrated that PFV, but not waist circumference, significantly associated with the presence of any coronary plaques (odds ratio [OR]; 2.876, 95% confidence interval [95% CI]; 1.614-5.125, p<0.001), nonstenotic plaques confirmed by coronary angiography (OR; 3.423, 95% CI; 1.764-6.642, p<0.001), and noncalcified plaques (OR; 3.316, 95% CI; 1.435-7.661, p<0.01).

CONCLUSIONS

PFV correlated significantly with the presence of nonstenotic and noncalcified coronary plaques assessed by multislice computed tomography. Pericardial fat is more highly associated with early development of CAD than simple anthropometric measures of abdominal obesity.

Macrophages from alpha 7 nicotinic acetylcholine receptor knockout mice demonstrate increased cholesterol accumulation and decreased cellular paraoxonase expression: a possible link between the nervous system and atherosclerosis development

OBJECTIVE

The parasympathetic nervous system regulates inflammation in peripheral tissues through a pathway termed the "cholinergic anti-inflammatory reflex" (CAIR). Mice deficient in the alpha 7 nicotinic acetylcholine receptor (alpha7(-/-)) have an impaired CAIR due to decreased signaling through this pathway. The purpose of this study was to determine if the increased inflammation in alpha7(-/-) mice is associated with enhanced serum and macrophage atherogenicity.

METHODS

We measured serum markers of inflammation and oxidative stress, and macrophage atherogenicity in mouse peritoneal macrophages harvested from alpha7(-/-) mice on the background of C57BL/6 mice, as well as on the background of the atherosclerotic Apolipoprotein E-deficient (ApoE(-/-)) mice.

RESULTS

alpha7-Deficiency had no significant effects on serum cholesterol, or on markers of serum oxidative stress (TBARS and paraoxonase1 activities). However, alpha7-deficiency significantly increased serum CRP and IL-6 (p<0.05) levels in atherosclerotic mice, confirming an anti-inflammatory role for the alpha7 receptor. Macrophage cholesterol mass was increased by 25% in both normal and atherosclerotic mice in the absence of the alpha7 receptor (p<0.05). This was accompanied by conditional increases in oxidized LDL uptake and in macrophage total peroxide levels. Furthermore, alpha7-deficiency reduced macrophage paraoxonase2 mRNA and activity by 50-100% in normal and atherosclerotic mice (p<0.05 for each), indicating a reduction in macrophage anti-oxidant capacity in the alpha7(-/-) mice.

CONCLUSION

The above results suggest an anti-atherogenic role for the macrophage alpha7nAchr, through a mechanism that involves attenuated macrophage oxidative stress and decreased uptake of oxidized LDL.

Obesity promotes inflammation in periaortic adipose tissue and angiotensin II-induced abdominal aortic aneurysm formation

OBJECTIVE

Obesity promotes macrophage infiltration into adipose tissue and is associated with increases in several cardiovascular diseases. Infusion of angiotensin II (AngII) to mice induces formation of abdominal aortic aneurysms (AAAs) with profound medial and adventitial macrophage infiltration. We sought to determine whether obesity promotes macrophage infiltration and proinflammatory cytokines in periaortic adipose tissue surrounding abdominal aortas and increases AngII-induced AAAs.

METHODS AND RESULTS

Hypertrophied white adipocytes surrounded abdominal aortas, whereas brown adipocytes surrounded thoracic aortas of obese mice. mRNA abundance of macrophage proinflammatory chemokines and their receptors were elevated with obesity to a greater extent in abdominal compared to thoracic periaortic adipose tissue. Periaortic adipose tissue explants surrounding abdominal aortas of obese mice released greater concentrations of MCP-1 and promoted more macrophage migration than explants from thoracic aortas. Male C57BL/6 mice were fed a high-fat (HF) diet for 1, 2, or 4 months and then infused with AngII (1000 ng/kg/min) for 28 days. AAA incidence increased progressively with the duration of HF feeding (18%, 36%,and 60%, respectively). Similarly, AngII-infused ob/ob mice exhibited increased AAAs compared to lean controls (76% compared to 32%, respectively, P<0.05). Infusion of AngII to obese mice promoted further macrophage infiltration into periaortic and visceral adipose tissue, and obese mice exhibiting AAAs had greater macrophage content in visceral adipose tissue than mice not developing AAAs.

CONCLUSIONS

Increased macrophage accumulation in periaortic adipose tissue surrounding abdominal aortas of AngII-infused obese mice is associated with enhanced AAA formation.

Increased epicardial adipose tissue (EAT) volume in type 2 diabetes mellitus and association with metabolic syndrome and severity of coronary atherosclerosis

OBJECTIVE

Epicardial adipose tissue (EAT) is a part of visceral fat deposited around the heart between the pericardium and myocardium along the distribution of coronary arteries. EAT thickness is reported to be associated with coronary atherosclerosis; however, no study has measured EAT volume in patients with type 2 diabetes or investigate its association with coronary artery disease.

DESIGN

A hospital-based case control study.

PATIENTS

A total of 49 patients with type 2 diabetes mellitus (T2DM) and 78 nondiabetic controls were studied.

MEASUREMENTS

Cardiac multislice computed tomography was used to measure EAT volume, Gensini score, coronary artery calcium score and, coronary lesions. The relationships between EAT volume, markers of coronary atherosclerosis and anthropometric and biochemical parameters of metabolic syndrome (MetS) were investigated.

RESULTS

EAT volume was significantly higher in patients with T2DM than in nondiabetic subjects (166.1 +/- 60.6 cm(3) vs. 123.4 +/- 41.8 cm(3), P < 0.0001). Logistic regression analysis revealed independent and significant associations between EAT and diabetic status. EAT volume was significantly associated with components of MetS (BMI, waist circumference, fasting serum glucose, total cholesterol, HDL-cholesterol, and triglycerides levels), Gensini score, coronary lesions, coronary disease and coronary calcium scores. Univariate, multivariate and trend analyses confirmed that EAT volume was associated with MetS component clustering and the coronary atherosclerosis index.

CONCLUSIONS

The analytical results indicate that EAT volume is increased in T2DM patients and is associated with unfavourable components of MetS and coronary atherosclerosis. The close anatomical relationship between EAT and the coronary arteries, combined with other evidence indicating that EAT is a biologically active adipokine-secreting tissue, suggest that EAT participates in the pathogenesis of diabetic coronary atherosclerosis.

Obstructive sleep apnea, immuno-inflammation, and atherosclerosis

Obstructive sleep apnea (OSA) is a highly prevalent sleep disorder leading to cardiovascular and metabolic complications. OSA is also a multicomponent disorder, with intermittent hypoxia (IH) as the main trigger for the associated cardiovascular and metabolic alterations. Indeed, recurrent pharyngeal collapses during sleep lead to repetitive sequences of hypoxia-reoxygenation. This IH induces several consequences such as hemodynamic, hormonometabolic, oxidative, and immuno-inflammatory alterations that may interact and aggravate each other, resulting in artery changes, from adaptive to degenerative atherosclerotic remodeling. Atherosclerosis has been found in OSA patients free of other cardiovascular risk factors and is related to the severity of nocturnal hypoxia. Early stages of artery alteration, including functional and structural changes, have been evidenced in both OSA patients and rodents experimentally exposed to IH. Impaired vasoreactivity with endothelial dysfunction and/or increased vasoconstrictive responses due to sympathetic, endothelin, and renin-angiotensin systems have been reported and also contribute to vascular remodeling and inflammation. Oxidative stress, inflammation, and vascular remodeling can be directly triggered by IH, further aggravated by the OSA-associated hormonometabolic alterations, such as insulin resistance, dyslipidemia, and adipokine imbalance. As shown in OSA patients and in the animal model, genetic susceptibility, comorbidities (obesity), and life habits (high fat diet) may aggravate atherosclerosis development or progression. The intimate molecular mechanisms are still largely unknown, and their understanding may contribute to delineate new targets for prevention strategies and/or development of new treatment of OSA-related atherosclerosis, especially in patients at risk for cardiovascular disease.

Pericardial adipose tissue determined by dual source CT is a risk factor for coronary atherosclerosis

OBJECTIVES

Pericardial fat as a visceral fat depot may be involved in the pathogenesis of coronary atherosclerosis. To gain evidence for that concept we sought to investigate the relation of pericardial fat volumes to risk factors, serum adiponectin levels, inflammatory biomarkers, and the quantity and morphology of coronary atherosclerosis.

METHODS AND RESULTS

Using Dual source CT angiography pericardial fat volume and coronary atherosclerosis were assessed simultaneously. Plaques were classified as calcified, mixed, and noncalcified, and the number of affected segments served as quantitative score. Patients with atherosclerotic lesions had significant larger PAT volumes (226 cm3+/-92 cm3) than patients without atherosclerosis (134 cm3+/-56 cm3; P>0.001). No association was found between BMI and coronary atherosclerosis. PAT volumes >300 cm3 were the strongest independent risk factor for coronary atherosclerosis (odds ratio 4.1; CI 3.63 to 4.33) also significantly stronger compared to the Framingham score. We furthermore demonstrated that elevated PAT volumes are significantly associated with low adiponectin levels, low HDL levels, elevated TNF-alpha levels, and hsCRP.

CONCLUSION

In the present study we demonstrated that elevated PAT volumes are associated with coronary atherosclerosis, hypoadiponectinemia, and inflammation and represent the strongest risk factor for the presence of atherosclerosis and may be important for risk stratification and monitoring.

Novel measurements of periaortic adipose tissue in comparison to anthropometric measures of obesity, and abdominal adipose tissue

BACKGROUND

Perivascular adipose tissue may be associated with the amount of local atherosclerosis. We developed a novel and reproducible method to standardize volumetric quantification of periaortic adipose tissue by computed tomography (CT) and determined the association with anthropometric measures of obesity, and abdominal adipose tissue.

METHODS

Measurements of adipose tissue were performed in a random subset of participants from the Framingham Heart Study (n=100) who underwent multidetector CT of the thorax (ECG triggering, 2.5 mm slice thickness) and the abdomen (helical CT acquisition, 2.5 mm slice thickness). Abdominal periaortic adipose tissue (AAT) was defined by a 5 mm cylindrical region of interest around the aortic wall; thoracic periaortic adipose tissue (TAT) was defined by anatomic landmarks. TAT and AAT were defined as any voxel between -195 and -45 HU and volumes were measured using dedicated semiautomatic software. Measurement reproducibility and association with anthropometric measures of obesity, and abdominal adipose tissue were determined.

RESULTS

The intra- and inter-observer reproducibility for both AAT and TAT was excellent (ICC: 0.97 and 0.97; 0.99 and 0.98, respectively). Similarly, the relative intra- and inter-observer difference was small for both AAT (-1.85+/-1.28% and 7.85+/-6.08%; respectively) and TAT (3.56+/-0.83% and -4.56+/-0.85%, respectively). Both AAT and TAT were highly correlated with visceral abdominal fat (r=0.65 and 0.77, P<0.0001 for both) and moderately correlated with subcutaneous abdominal fat (r=0.39 and 0.42, P<0.0001 and P=0.009), waist circumference (r=0.49 and 0.57, P<0.0001 for both) and body mass index (r=0.47 and 0.58, P<0.0001 for both).

CONCLUSION

Standardized semiautomatic CT-based volumetric quantification of periaortic adipose tissue is feasible and highly reproducible. Further investigation is warranted regarding associations of periaortic adipose tissue with other body fat deposits, cardiovascular risk factors and clinical outcomes.

Genomic Modeling of Atherosclerosis in Peripheral Arterial Disease and Its Variant Phenotype in Patients with Diabetes

Microarrays can be used to discover candidate genes associated with peripheral arterial disease (PAD) and develop models that predict patient clinical status. We hypothesize that multiple phenotypes of PAD with distinct patterns of gene expression exist. We histologically characterized and extracted ribonucleic acid from 31 arterial samples collected from the lower extremities of patients undergoing amputation or free fibular grafting. Analysis using the Affymetrix U133A microarray identified 335 genes with twofold or greater differences in expression between normal and diseased arteries ( p < .01) and 104 genes with twofold or greater differences between diabetic and nondiabetic atherosclerotic arteries ( p < .1). Many genes identified have known roles in inflammatory and lipid uptake pathways. Predictive models were developed that could predict PAD and the associated diabetic phenotype with an accuracy of 71 to 90%. Developing distinct genomic models of PAD will serve as the first step toward understanding the molecular and genetic basis of PAD and subsequent application of novel therapeutics to this condition.

Visceral obesity and the heart

Obesity and particularly its deleterious form, visceral adiposity, has reached a high prevalence in the industrialized world owing to the lack of exercise and the widely available energy-dense diet. As a consequence, cardiovascular diseases and metabolic disorders are afflicting an unprecedented number of individuals at a world-wide scale. Over the last decades, investigations have established firm links between visceral obesity and the development of cardiovascular diseases. Moreover, studies in the field of lipid partitioning have demonstrated that inadequacy of homeostatic mechanism ensuring adequate handling of energy surplus is associated with accumulation of visceral fat and lipid overload of internal organs, which are participating to the development of heart diseases. Visceral obesity and its metabolic consequences often referred to as the metabolic syndrome is associated with the production of an atherosclerosis prone milieu. In this review, clinical implications of visceral obesity on the development of cardiovascular disorders are reviewed along with important mechanisms participating to the development of these disorders. Implications and failure of lipid partitioning and some of the potential pathways mediating development of heart diseases are also covered in view of recent development of therapeutic options.