Implications of Pericardial, Visceral and Subcutaneous Adipose Tissue on Vascular Inflammation Measured Using 18FDG-PET/CT

MRI-based quantification of adipose tissue distribution in healthy adult cats during body weight gain

The incidence of obesity in pet population increased over the last decades. Cats have been suggested as model for human obesity because of similar co-morbidities as diabetes and dyslipidaemia. Aim of this study were to quantify the distribution of visceral and subcutaneous adipose tissue (VAT, SAT respectively) in healthy adult cats during feeding-induced body weight (BW) gain by MRI, and to correlate it to the increased hepatic fat fraction (HFF). Cats received a commercial dry food ad libitum for 40 weeks and were longitudinally scanned three times. VAT and SAT were determined from Dixon MRI data by a dedicated software solution (ATLAS, established in human and rodents). HFF was quantified from a commercially available sequence. At both individual and group level, normalized adipose tissue volumes significantly increased longitudinally, with median VAT/SAT ratio always < 1. With increased BW, more than proportional increased total adipose tissue was observed together with more than proportional increased HFF. HFF is disproportionately high in overweight cats compared to SAT and VAT accumulation in the 40 weeks observation period. Quantitative unbiased MRI examination of different body fat components is useful in longitudinal monitoring of obesity in cats.

Pitfalls and challenges of the purinergic signaling cascade in obesity

Obesity is a worldwide health problem which have reached pandemic proportions, now also including low and middle-income countries. Excessive or abnormal fat deposition in the abdomen especially in the visceral compartment is tightly associated with a high metabolic risk for arterial hypertension, type II diabetes, cardiovascular diseases, musculoskeletal disorders (especially articular degeneration) and some cancers. Contrariwise, accumulation of fat in the subcutaneous compartment has been associated with a neutral metabolic impact, favoring a lower risk of insulin resistance. Obesity results more often from an avoidable imbalance between food consumption and energy expenditure. There are several recommended strategies for dealing with obesity, including pharmacological therapies, but their success remains incomplete and may not compensate the associated adverse effects. Purinergic signaling operated by ATP and its metabolite, adenosine, has attracted increasing attention in obesity. The extracellular levels of purines often reflect the energy status of a given cell population. Adenine nucleotides and nucleosides fine tuning control adipogenesis and mature adipocytes function via the activation of P2 and P1 purinoceptors, respectively. These features make the purinergic signaling cascade a putative target for therapeutic intervention in obesity and related metabolic syndromes. There are, however, gaps in our knowledge regarding the role of purines in adipocyte precursors differentiation and mature adipocytes functions, as well as their impact among distinct adipose tissue deposits (e.g. white vs. brown, visceral vs. subcutaneous), which warrants further investigations before translation to clinical trials can be made.

Visceral adipose tissue volume is associated with premature atherosclerosis in early type 2 diabetes mellitus independent of traditional risk factors

BACKGROUND AND AIMS

Type 2 diabetes mellitus (T2DM) is commonly associated with abdominal obesity, predominantly with high visceral adipose tissue (VAT), and is accompanied by premature atherosclerosis. However, the association between VAT and subcutaneous adipose tissue (SAT) with premature atherosclerosis and (i.e. arterial) inflammation is not completely understood. To provide more insight into this association, we investigated the association between arterial ¹⁸F-fluordeoxyglucose (FDG) positron emission tomography (PET) uptake, as a measure of arterial inflammation, and metabolic syndrome (MetS) markers in early T2DM patients.

METHODS

Forty-four patients with early T2DM, without glucose lowering medication, were studied (median age 63 [IQR 54-66] years, median BMI 30.4 [IQR 27.5-35.8]). Arterial inflammation was quantified using glucose corrected maximum standardized uptake value (SUV_max) FDG of the aorta, carotid, iliac, and femoral arteries, and corrected for background activity (blood pool) as target-to-background ratio (_meanTBR). VAT and SAT volumes (cm³) were automatically segmented using computed tomography (CT) between levels L1-L5. Non-alcoholic fatty liver disease (NAFLD) was assessed by liver function test and CT.

RESULTS

VAT volume, but not SAT volume, correlated with _meanTBR (r = 0.325, p = 0.031). Linear regression models showed a significant association, even after sequential adjustment for potentially influencing MetS components. Interaction term VAT volume * sex and additional components including HbA1c, insulin resistance, NAFLD, adiponectin, leptin, and C- reactive protein (CRP) did not change the independent association between VAT volume and _meanTBR.

CONCLUSIONS

CT-assessed VAT volume is positively associated with FDG-PET assessed arterial inflammation, independently of factors thought to potentially mediate these effects. These findings suggest that VAT in contrast to SAT is linked to early atherosclerotic changes in T2DM patients.

Coronary Artery Spasm and Perivascular Adipose Tissue Inflammation: Insights From Translational Imaging Research

Perivascular adipose tissue, which constitutes perivascular components along with the adventitial vasa vasorum, plays an important role as a source of various inflammatory mediators in cardiovascular disease. Inflammatory changes in the coronary adventitia are thought to be involved in the pathogenesis of coronary artery spasm and vasospastic angina. Recent advances in translational research using non-invasive imaging modalities, including ¹⁸F-fluorodeoxyglucose PET and cardiac CT, have enabled us to visualise perivascular inflammation in the pathogenesis of coronary artery spasm. These modality approaches appear to be clinically useful as a non-invasive tool for examining the presence and severity of vasospastic angina.

Atherosclerotic plaque burden evaluated from neck to groin: effect of gender and cardiovascular risk factors

We explored the impact of gender and cardiovascular risk factors (RF) in the distribution and burden of coronary and extra-coronary atherosclerotic plaques among patients undergoing ECG-gated thoracoabdominal computed tomography angiography (CTA) from the supra-aortic trunks to the femoral arteries. We included a consecutive cohort of patients who underwent ECG-gated thoracoabdominal aortic CTA from the supra-aortic trunks to the pubic symphysis. We evaluated the number of coronary segments with plaques [segment-involvement score (SIS)]; and the extra-coronary atherosclerotic plaque burden, comprising the aorta and supra-aortic trunks, iliofemoral arteries, and visceral arteries (extra-coronary SS). A total of 3400 vascular segments were evaluated in 100 patients (mean age 67.0 ± 12.6 years, 66% male). Seventy-two (72%) patients had evidence of atherosclerosis in the coronary tree (coronary SIS ≥ 1), of which 32% was extensive (coronary SIS > 5). Males had a significantly higher prevalence of coronary SIS ≥ 1 [53 (80%), vs. 19 (56%), p = 0.018], and coronary SIS > 5 [24 (36%) vs. 8 (24%), p = 0.035] than females. Extra-coronary SS was similar between genders (males 10.2 ± 5.8 vs. females 9.7 ± 5.4, p = 0.70), irrespective of the location along the different vascular beds. The number of coronary RF was significantly related to the coronary SIS (p = 0.038), and hypertension and diabetes were consistently related to coronary and extra-coronary plaque burden. In the present study involving analysis of multiple vascular beds from the supra-aortic trunks to the femoral arteries, we identified significant sex-related differences in coronary plaque burden, whereas extra-coronary plaque burden was similar between genders irrespective of the vascular bed assessed.

Diet-Modulated Lipoprotein Metabolism and Vascular Inflammation Evaluated by 18F-fluorodeoxyglucose Positron Emission Tomography

Vascular inflammation plays a central role in atherosclerosis, from initiation and progression to acute thrombotic complications. Modified low-density lipoproteins (LDLs) and apoB-containing particles stimulate plaque inflammation by interacting with macrophages. Loss of function of high-density lipoprotein (HDL) for preventing LDL particles from oxidative modification in dyslipidemic states may amplify modified LDL actions, accelerating plaque inflammation. Diets are one of the most important factors that can affect these processes of lipoprotein oxidation and vascular inflammation. Recently, ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) has emerged as a reliable noninvasive imaging modality for identifying and quantifying vascular inflammation within atherosclerotic lesions based on the high glycolytic activity of macrophages infiltrating active atherosclerotic plaques. Vascular inflammation evaluated by FDG PET has been positively related to metabolic syndrome components and traditional risk factors of cardiovascular disease, including high-sensitivity C-reactive protein, body mass index, and insulin resistance. A positive association of vascular inflammation with endothelial dysfunction, resistin levels, pericardial adipose tissue, and visceral fat area has also been reported. In contrast, HDL cholesterol and adiponectin have been inversely related to vascular inflammation detected by FDG PET. Because of its reproducibility, serial FDG PET shows potential for tracking the effects of dietary interventions and other systemic and local antiatherosclerotic therapies for plaque inflammation.

Correlations between the abdominal fat-related parameters and severity of coronary artery disease assessed by computed tomography

Background

Obesity is considered a challenging public problem, which has been proven to be closely associated with coronary artery disease (CAD). Each risk factor of CAD has been separately studied many times in the past, but very few have comprehensively and quantitatively evaluated the relationship between the abdominal fat-related parameters and severity of CAD. The aim of this study was to analyze whether the abdominal fat-related parameters were associated with severity of CAD using abdominal non-enhanced computed tomography (NECT).

Methods

Patients who went through both abdominal NECT and invasive coronary angiography (ICA) were included and retrospectively analyzed. The abdominal fat-related parameters [the ratio of visceral adipose tissue to subcutaneous adipose tissue (VAT/SAT ratio)] and traditional cardiovascular risk factors were evaluated in the participants with or without obstructive CAD. The correlations between the abdominal fat-related parameters and severity of CAD were assessed, and the multivariable logistic regression analysis was performed to investigate the parameters that could be used to predict the severity of CAD.

Results

A total of 223 consecutive subjects (obstructive CAD group, n=117; non-obstructive CAD group, n=106) were analyzed. The VAT/SAT ratio was significantly higher (0.95±0.33 vs. 0.70±0.25, P<0.001) in obstructive CAD (O-CAD) patients than that in non-obstructive CAD (NO-CAD) patients. There was a trend to having nonalcoholic fatty liver disease (NAFLD) in the O-CAD patients than that of NO-CAD (P=0.002); the abdominal aortic calcification (AAC) score in O-CAD patients were higher than that in NO-CAD patients (P<0.001). The multivariable logistic regression analysis demonstrated that VAT/SAT ratio, NAFLD, and AAC score were independent predictors of O-CAD after adjusting the traditional cardiovascular risk factors. The area under the curve (AUC) of the combination of the above risk factors is 0.85, which leads to an increase in AUC than each risk factor alone in differentiating patients with or without O-CAD.

Conclusions

VAT/SAT ratio, NAFLD, and AAC score are correlated with the severity of CAD, indicating their characteristics of being independent risk factors for O-CAD, irrespective of the traditional cardiovascular risk factors. Those CT-derived parameters may make positive contributions to the differentiation of the patients with increased risk of O-CAD.

Alterations to adipose tissue morphology during inflammatory arthritis is indicative of vasculopathology in DBA/1 mice

The physiologic function of adipose tissue is altered by the host's inflammatory response; the implications for maintaining human health and regulating inflammation-associated disease progression are ill defined. However, this cannot be investigated in humans, therefore the use of animal models is required. With the aim to determine morphological and molecular alterations to perivascular and organ-associated adipose tissues during inflammatory arthritis, collagen-induced arthritis (CIA) was established in male DBA/1 mice. Emerging evidence from this study signposts CIA in the DBA/1 mouse as a model that is relevant to study the development and treatment of early cardiovascular pathology associated with inflammatory arthritis. Here, we show global morphological changes in adipose tissue and the thoracic aorta in animals induced with CIA compared with the non-immunized controls. In CIA, we concluded that the increased cell count in PVAT was, at least in part, caused by an ingress and/or expansion of macrophages that had a mixed phenotype. A substantial increase of galectin-3 was expressed in PVAT from mice with CIA. Galectin-3 is elevated in the blood of patients with CVDs, however, it has never before been measured in PVAT in rodents or humans. Here, PVAT-associated galectin-3 is identified as a potential biomarker for detecting early vascular pathology in CIA and a promising candidate for translation to RA.

The Ratio Between Visceral and Subcutaneous Abdominal Fat Assessed by Computed Tomography Is an Independent Predictor of Mortality and Cardiac Events

INTRODUCTION AND OBJECTIVES

Obesity is an important cardiovascular risk factor and the location of fat deposits seems to be an important determinant of its metabolic impact. Visceral adipose tissue (VAT) exerts a harmful effect on metabolic homeostasis, but few longitudinal studies have evaluated the prognostic impact of the ratio of VAT to subcutaneous adipose tissue (SAT). This study aimed to evaluate whether the VAT/SAT ratio was associated with all-cause mortality and cardiac events.

METHODS

Registry-based retrospective cohort study. Eligible patients consisted of those without known heart disease referred to cardiac computed tomography (CT) angiography to evaluate suspected coronary artery disease (CAD). We included all patients with available information on VAT and SAT areas and coronary artery calcium (CAC) score. We assessed the combined endpoint of all-cause mortality, myocardial infarction or revascularization procedure at least 1 month after cardiac CT.

RESULTS

The final population consisted of 713 participants (61% male; mean age, 57.7±10.2 years) followed up for a median of 1.3 years. The combined endpoint occurred in 66 patients; these patients showed a higher VAT/SAT ratio (1.06±0.74 vs 0.80±0.52, P=.0001). The VAT/SAT ratio was an independent predictor of death and cardiac events (HR = 1.43; 95%CI, 1.03-1.99), irrespective of cardiovascular risk factors, CAC, and the presence of CAD.

CONCLUSIONS

The ratio between abdominal VAT/SAT was an independent predictor of death and coronary events, irrespective of cardiovascular risk factors, CAC, and the presence of CAD. This ratio is a CT-derived metric that may help to better identify patients with increased risk of death or cardiac events.

Type 2 diabetes enhances arterial uptake of choline in atherosclerotic mice: an imaging study with positron emission tomography tracer ¹⁸F-fluoromethylcholine

Background

Diabetes is a risk factor for atherosclerosis associated with oxidative stress, inflammation and cell proliferation. The purpose of this study was to evaluate arterial choline uptake and its relationship to atherosclerotic inflammation in diabetic and non-diabetic hypercholesterolemic mice.

Methods

Low-density lipoprotein-receptor deficient mice expressing only apolipoprotein B100, with or without type 2 diabetes caused by pancreatic overexpression of insulin-like growth factor II (IGF-II/LDLR^−/−ApoB^100/100 and LDLR^−/−ApoB^100/100) were studied. Distribution kinetics of choline analogue ¹⁸F-fluoromethylcholine (¹⁸F-FMCH) was assessed in vivo by positron emission tomography (PET) imaging. Then, aortic uptakes of ¹⁸F-FMCH and glucose analogue ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG), were assessed ex vivo by gamma counting and autoradiography of tissue sections. The ¹⁸F-FMCH uptake in atherosclerotic plaques was further compared with macrophage infiltration and the plasma levels of cytokines and metabolic markers.

Results

The aortas of all hypercholesterolemic mice showed large, macrophage-rich atherosclerotic plaques. The plaque burden and densities of macrophage subtypes were similar in diabetic and non-diabetic animals. The blood clearance of ¹⁸F-FMCH was rapid. Both the absolute ¹⁸F-FMCH uptake in the aorta and the aorta-to-blood uptake ratio were higher in diabetic than in non-diabetic mice. In autoradiography, the highest ¹⁸F-FMCH uptake co-localized with macrophage-rich atherosclerotic plaques. ¹⁸F-FMCH uptake in plaques correlated with levels of total cholesterol, insulin, C-peptide and leptin. In comparison with ¹⁸F-FDG, ¹⁸F-FMCH provided similar or higher plaque-to-background ratios in diabetic mice.

Conclusions

Type 2 diabetes enhances the uptake of choline that reflects inflammation in atherosclerotic plaques in mice. PET tracer ¹⁸F-FMCH is a potential tool to study vascular inflammation associated with diabetes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0340-6) contains supplementary material, which is available to authorized users.