Megan H. MacNabb

HIF-1α and PFKFB3 Mediate a Tight Relationship Between Proinflammatory Activation and Anerobic Metabolism in Atherosclerotic Macrophages

Objective—Although it is accepted that macrophage glycolysis is upregulated under hypoxic conditions, it is not known whether this is linked to a similar increase in macrophage proinflammatory activation and whether specific energy demands regulate cell viability in the atheromatous plaque. Approach and Results—We studied the interplay between macrophage energy metabolism, polarization, and viability in the context of atherosclerosis. Cultured human and murine macrophages and an in vivo murine model of atherosclerosis were used to evaluate the mechanisms underlying metabolic and inflammatory activity of macrophages in the different atherosclerotic conditions analyzed. We observed that macrophage energetics and inflammatory activation are closely and linearly related, resulting in dynamic calibration of glycolysis to keep pace with inflammatory activity. In addition, we show that macrophage glycolysis and proinflammatory activation mainly depend on hypoxia-inducible factor and on its impact on glucose uptake, and on the expression of hexokinase II and ubiquitous 6-phosphofructo-2-kinase. As a consequence, hypoxia potentiates inflammation and glycolysis mainly via these pathways. Moreover, when macrophages’ ability to increase glycolysis through 6-phosphofructo-2-kinase is experimentally attenuated, cell viability is reduced if subjected to proinflammatory or hypoxic conditions, but unaffected under control conditions. In addition to this, granulocyte-macrophage colony-stimulating factor enhances anerobic glycolysis while exerting a mild proinflammatory activation. Conclusions—These findings, in human and murine cells and in an animal model, show that hypoxia potentiates macrophage glycolytic flux in concert with a proportional upregulation of proinflammatory activity, in a manner that is dependent on both hypoxia-inducible factor -1&agr; and 6-phosphofructo-2-kinase.

Nonpharmacological Lipoprotein Apheresis Reduces Arterial Inflammation in Familial Hypercholesterolemia

BACKGROUND Patients with familial hypercholesterolemia (FH) are characterized by elevated atherogenic lipoprotein particles, predominantly low-density lipoprotein cholesterol (LDL-C), which is associated with accelerated atherogenesis and increased cardiovascular risk. OBJECTIVES This study used (18)F-fluorodeoxyglucose positron emission tomography ((18)FDG-PET) to investigate whether arterial inflammation is higher in patients with FH and, moreover, whether lipoprotein apheresis attenuates arterial wall inflammation in FH patients. METHODS In total, 38 subjects were recruited: 24 FH patients and 14 normolipidemic controls. All subjects underwent FDG-PET imaging at baseline. Twelve FH patients who met the criteria for lipoprotein apheresis underwent apheresis procedures followed by a second FDG-PET imaging 3 days (range 1 to 4 days) after apheresis. Subsequently, the target-to-background ratio (TBR) of FDG uptake within the arterial wall was assessed. RESULTS In FH patients, the mean arterial TBR was higher compared with healthy controls (2.12 ± 0.27 vs. 1.92 ± 0.19; p = 0.03). A significant correlation was observed between baseline arterial TBR and LDL-C (R = 0.37; p = 0.03) that remained significant after adjusting for statin use (β = 0.001; p = 0.02) and atherosclerosis risk factors (β = 0.001; p = 0.03). LDL-C levels were significantly reduced after lipoprotein apheresis (284 ± 118 mg/dl vs. 127 ± 50 mg/dl; p < 0.001). There was a significant reduction of arterial inflammation after lipoprotein apheresis (TBR: 2.05 ± 0.31 vs. 1.91 ± 0.33; p < 0.02). CONCLUSIONS The arterial wall of FH patients is characterized by increased inflammation, which is markedly reduced after lipoprotein apheresis. This lends support to a causal role of apoprotein B-containing lipoproteins in arterial wall inflammation and supports the concept that lipoprotein-lowering therapies may impart anti-inflammatory effects by reducing atherogenic lipoproteins.

Increased arterial inflammation relates to high-risk coronary plaque morphology in HIV-infected patients.

Background:Mechanisms predisposing HIV-infected patients to increased cardiovascular disease (CVD) risk remain unclear. Objective:To determine the interrelationship between arterial inflammation and high-risk coronary plaque morphology in HIV-infected patients with subclinical coronary atherosclerosis. Methods:Forty-one HIV-infected patients on stable antiretroviral therapy without known CVD but with atherosclerotic plaque on coronary CT angiography were evaluated with 18F-FDG-PET. Patients were stratified into 2 groups based on relative degree of arterial inflammation [aortic target-to-background ratio (TBR)]. High-risk coronary atherosclerotic plaque morphology features were compared between groups. Results:HIV-infected patients with higher and lower TBRs were similar with respect to traditional CVD risk parameters. Among HIV-infected patients with higher TBR, an increased percentage of patients demonstrated at least 1 low-attenuation coronary atherosclerotic plaque (40% vs. 10%, P = 0.02) and at least 1 coronary atherosclerotic plaque with both low attenuation and positive remodeling (35% vs. 10%, P = 0.04). Moreover, in the higher TBR group, both the number of low-attenuation plaques per patient (P = 0.02) and the number of vulnerability features in the most vulnerable plaque (P = 0.02) were increased. TBR grouping remained significantly related to the number of low-attenuation plaques/subject (&bgr; = 0.35, P = 0.004), controlling for age, gender, low-density lipoprotein, duration of HIV, and CD4. Conclusions:These data demonstrate a relationship between arterial inflammation on 18F-FDG-PET and high-risk coronary atherosclerotic plaque features among HIV-infected patients with subclinical coronary atherosclerosis. Further studies are needed to determine whether arterial inflammation and related high-risk coronary morphology increase the risk of clinical CVD events in the HIV population.

18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Enables the Detection of Recurrent Same-Site Deep Vein Thrombosis by Illuminating Recently Formed, Neutrophil-Rich Thrombus

Background— Accurate detection of recurrent same-site deep vein thrombosis (DVT) is a challenging clinical problem. Because DVT formation and resolution are associated with a preponderance of inflammatory cells, we investigated whether noninvasive 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) imaging could identify inflamed, recently formed thrombi and thereby improve the diagnosis of recurrent DVT. Methods and Results— We established a stasis-induced DVT model in murine jugular veins and also a novel model of recurrent stasis DVT in mice. C57BL/6 mice (n=35) underwent ligation of the jugular vein to induce stasis DVT. FDG-PET/computed tomography (CT) was performed at DVT time points of day 2, 4, 7, 14, or 2+16 (same-site recurrent DVT at day 2 overlying a primary DVT at day 16). Antibody-based neutrophil depletion was performed in a subset of mice before DVT formation and FDG-PET/CT. In a clinical study, 38 patients with lower extremity DVT or controls undergoing FDG-PET were analyzed. Stasis DVT demonstrated that the highest FDG signal occurred at day 2, followed by a time-dependent decrease (P<0.05). Histological analyses demonstrated that thrombus neutrophils (P<0.01), but not macrophages, correlated with thrombus PET signal intensity. Neutrophil depletion decreased FDG signals in day 2 DVT in comparison with controls (P=0.03). Recurrent DVT demonstrated significantly higher FDG uptake than organized day 14 DVT (P=0.03). The FDG DVT signal in patients also exhibited a time-dependent decrease (P<0.01). Conclusions— Noninvasive FDG-PET/CT identifies neutrophil-dependent thrombus inflammation in murine DVT, and demonstrates a time-dependent signal decrease in both murine and clinical DVT. FDG-PET/CT may offer a molecular imaging strategy to accurately diagnose recurrent DVT.

Contrast-Enhanced Ultrasound: A Novel Noninvasive, Nonionizing Method for the Detection of Brown Adipose Tissue in Humans

BACKGROUND Brown adipose tissue (BAT) consumes glucose when it is activated by cold exposure, allowing its detection in humans by (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) with computed tomography (CT). The investigators recently described a novel noninvasive and nonionizing imaging method to assess BAT in mice using contrast-enhanced ultrasound (CEUS). Here, they report the application of this method in healthy humans. METHODS Thirteen healthy volunteers were recruited. CEUS was performed before and after cold exposure in all subjects using a continuous intravenous infusion of perflutren gas-filled lipid microbubbles and triggered imaging of the supraclavicular space. The first five subjects received microbubbles at a lower infusion rate than the subsequent eight subjects and were analyzed as a separate group. Blood flow was estimated as the product of the plateau (A) and the slope (β) of microbubble replenishment curves. All underwent (18)F-FDG PET/CT after cold exposure. RESULTS An increase in the acoustic signal was noted in the supraclavicular adipose tissue area with increasing triggering intervals in all subjects, demonstrating the presence of blood flow. The area imaged by CEUS colocalized with BAT, as detected by ¹⁸F-FDG PET/CT. In a cohort of eight subjects with an optimized CEUS protocol, CEUS-derived BAT blood flow increased with cold exposure compared with basal BAT blood flow in warm conditions (median Aβ = 3.3 AU/s [interquartile range, 0.5-5.7 AU/s] vs 1.25 AU/s [interquartile range, 0.5-2.6 AU/s]; P = .02). Of these eight subjects, five had greater than twofold increases in blood flow after cold exposure; these responders had higher BAT activity measured by (18)F-FDG PET/CT (median maximal standardized uptake value, 2.25 [interquartile range, 1.53-4.57] vs 0.51 [interquartile range, 0.47-0.73]; P = .02). CONCLUSIONS The present study demonstrates the feasibility of using CEUS as a noninvasive, nonionizing imaging modality in estimating BAT blood flow in young, healthy humans. CEUS may be a useful and scalable tool in the assessment of BAT and BAT-targeted therapies.

Relationship Between Measures of Adiposity, Arterial Inflammation, and Subsequent Cardiovascular Events

Background—The objective of this study was to evaluate how different measures of adiposity are related to both arterial inflammation and the risk of subsequent cardiovascular events. Methods and Results—We included individuals who underwent 18F-fluorodeoxyglucose positron emission tomography/computed tomography imaging for oncological evaluation. Subcutaneous adipose tissue (SAT) volume, visceral adipose tissue (VAT) volume, and VAT/SAT ratio were determined. Additionally, body mass index, metabolic syndrome, and aortic 18F-fluorodeoxyglucose uptake (a measure of arterial inflammation) were determined. Subsequent development of cardiovascular disease (CVD) events was adjudicated. The analysis included 415 patients with a median age of 55 (P25–P75: 45–65) and a median body mass index of 26.4 (P25–P75: 23.4–30.9) kg/m2. VAT and SAT volume were significantly higher in obese individuals. VAT volume (r=0.290; P<0.001) and VAT/SAT ratio (r=0.208; P<0.001) were positively correlated with arterial inflammation. Thirty-two subjects experienced a CVD event during a median follow-up of 4 years. Cox proportional hazard models showed that VAT volume and VAT/SAT ratio were associated with CVD events (hazard ratio [95% confidence interval]: 1.15 [1.06–1.25]; P<0.001; 3.60 [1.88–6.92]; P<0.001, respectively). Body mass index, metabolic syndrome, and SAT were not predictive of CVD events. Conclusions—Measures of visceral fat are positively related to arterial inflammation and are independent predictors of subsequent CVD events. Individuals with higher measures of visceral fat as well as elevated arterial inflammation are at highest risk for subsequent CVD events. The findings suggest that arterial inflammation may explain some of the CVD risk associated with adiposity.

Increased arterial inflammation in individuals with stage 3 chronic kidney disease

PurposeWhile it is well known that patients with chronic kidney disease (CKD) are at increased risk for the development and progression of atherosclerosis, it is not known whether arterial inflammation is increased in mild CKD. The aim of this study was to compare arterial inflammation using 18F-FDG PET/CT in patients with CKD and in matched controls.MethodsThis restrospective study included 128 patients undergoing FDG PET/CT imaging for clinical indications, comprising 64 patients with stage 3 CKD and 64 control patients matched by age, gender, and cancer history. CKD was defined according to guidelines using a calculated glomerular filtration rate (eGFR). Arterial inflammation was measured in the ascending aorta as FDG uptake on PET. Background FDG uptake (venous, subcutaneous fat and muscle) were recorded. Coronary artery calcification (CAC) was assessed using the CT images. The impact of CKD on arterial inflammation and CAC was then assessed.ResultsArterial inflammation was higher in patients with CKD than in matched controls (standardized uptake value, SUV: 2.41 ± 0.49 vs. 2.16 ± 0.43; p = 0.002). Arterial SUV correlated inversely with eGFR (r = −0.299, p = 0.001). Venous SUV was also significantly elevated in patients with CKD, while subcutaneous fat and muscle tissue SUVs did not differ between groups. Moreover, arterial SUV remained significantly elevated in patients with CKD compared to controls after correcting for muscle and fat background, and also remained significant after adjusting for clinical risk factors. Further, CKD was associated with arterial inflammation (SUV) independent of the presence of subclinical atherosclerosis (CAC).ConclusionModerate CKD is associated with increased arterial inflammation beyond that of controls. Further, the increased arterial inflammation is independent of presence of subclinical atherosclerosis. Current risk stratification tools may underestimate the presence of atherosclerosis in patients with CKD and thereby the risk of cardiovascular events.

Response to Letter Regarding Article, “18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Enables the Detection of Recurrent Same-Site Deep Vein Thrombosis by Illuminating Recently Formed, Neutrophil-Rich Thrombus”

We thank Dr Klok and colleagues for their comments on our article.1 Deep venous thrombosis (DVT) is a relatively common disorder that is associated with potentially deadly complications, such as pulmonary embolism, and carries a substantial risk for the postthrombotic syndrome and recurrent DVT. Novel strategies are needed to predict and ultimately to reduce the development of such DVT-related complications. It is in this context that our group recently presented a novel application of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) imaging of inflammation to detect recurrent DVT, a vexing clinical problem insufficiently addressed by duplex ultrasound.1 In their letter, Klok et al posed questions about aspects of the clinical substudy reported in our article. We wish to provide some answers to their inquiries. One …

INCREASED BONE MARROW METABOLIC ACTIVITY IS ASSOCIATED WITH INCREASED RISK OF FUTURE CARDIOVASCULAR EVENTS

Bone marrow (BM) metabolic activity is increased after ACS and is associated with release of pro-inflammatory leukocytes and arterial inflammation. However, the relationship of BM activity to cardiovascular disease (CVD) events remains unknown. We identified 513 individuals free of cancer or prior