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Bone marrow adipose tissue (BMAT) comprises >10% of total adipose mass, yet unlike white or brown adipose tissues (WAT or BAT) its metabolic functions remain unclear. Herein, we address this critical gap in knowledge. Our transcriptomic analyses revealed that BMAT is distinct from WAT and BAT, with altered glucose metabolism and decreased insulin responsiveness. We therefore tested these functions in mice and humans using positron emission tomography-computed tomography (PET/CT) with 18 F-fluorodeoxyglucose. This revealed that BMAT resists insulin-and cold-stimulated glucose uptake, while further in vivo studies showed that, compared to WAT, BMAT resists insulin-stimulated Akt phosphorylation. Thus, BMAT is functionally distinct from WAT and BAT. However, in humans basal glucose uptake in BMAT is greater than in axial bones or subcutaneous WAT and can be greater than that in skeletal muscle, underscoring the potential of BMAT to influence systemic glucose homeostasis. These PET/CT studies characterise BMAT function in vivo, establish new methods for BMAT analysis, and identify BMAT as a distinct, major adipose tissue subtype.

BackgroundFluorine-18–sodium fluoride (18F-NaF) uptake is a marker of active vascular calcification associated with high-risk atherosclerotic plaque.ObjectivesIn patients with abdominal aortic aneurysm (AAA), the authors assessed whether 18F-NaF positron emission tomography (PET) and computed tomography (CT) predicts AAA growth and clinical outcomes.MethodsIn prospective case-control (n = 20 per group) and longitudinal cohort (n = 72) studies, patients with AAA (aortic diameter >40 mm) and control subjects (aortic diameter <30 mm) underwent abdominal ultrasound, 18F-NaF PET-CT, CT angiography, and calcium scoring. Clinical endpoints were aneurysm expansion and the composite of AAA repair or rupture.ResultsFluorine-18-NaF uptake was increased in AAA compared with nonaneurysmal regions within the same aorta (p = 0.004) and aortas of control subjects (p = 0.023). Histology and micro-PET-CT demonstrated that 18F-NaF uptake localized to areas of aneurysm disease and active calcification. In 72 patients within the longitudinal cohort study (mean age 73 ± 7 years, 85% men, baseline aneurysm diameter 48.8 ± 7.7 mm), there were 19 aneurysm repairs (26.4%) and 3 ruptures (4.2%) after 510 ± 196 days. Aneurysms in the highest tertile of 18F-NaF uptake expanded 2.5× more rapidly than those in the lowest tertile (3.10 [interquartile range (IQR): 2.34 to 5.92 mm/year] vs. 1.24 [IQR: 0.52 to 2.92 mm/year]; p = 0.008) and were nearly 3× as likely to experience AAA repair or rupture (15.3% vs. 5.6%; log-rank p = 0.043).ConclusionsFluorine-18-NaF PET-CT is a novel and promising approach to the identification of disease activity in patients with AAA and is an additive predictor of aneurysm growth and future clinical events. (Sodium Fluoride Imaging of Abdominal Aortic Aneurysms [SoFIA3]; NCT02229006; Magnetic Resonance Imaging [MRI] for Abdominal Aortic Aneurysms to Predict Rupture or Surgery: The MA3RS Trial; ISRCTN76413758)

BackgroundBioprosthetic aortic valve degeneration is increasingly common, often unheralded, and can have catastrophic consequences.ObjectivesThe authors sought to assess whether 18F-fluoride positron emission tomography (PET)-computed tomography (CT) can detect bioprosthetic aortic valve degeneration and predict valve dysfunction.MethodsExplanted degenerate bioprosthetic valves were examined ex vivo. Patients with bioprosthetic aortic valves were recruited into 2 cohorts with and without prosthetic valve dysfunction and underwent in vivo contrast-enhanced CT angiography, 18F-fluoride PET, and serial echocardiography during 2 years of follow-up.ResultsAll ex vivo, degenerate bioprosthetic valves displayed 18F-fluoride PET uptake that colocalized with tissue degeneration on histology. In 71 patients without known bioprosthesis dysfunction, 14 had abnormal leaflet pathology on CT, and 24 demonstrated 18F-fluoride PET uptake (target-to-background ratio 1.55 [interquartile range (IQR): 1.44 to 1.88]). Patients with increased 18F-fluoride uptake exhibited more rapid deterioration in valve function compared with those without (annualized change in peak transvalvular velocity 0.30 [IQR: 0.13 to 0.61] vs. 0.01 [IQR: −0.05 to 0.16] ms−1/year; p < 0.001). Indeed 18F-fluoride uptake correlated with deterioration in all the conventional echocardiographic measures of valve function assessed (e.g., change in peak velocity, r = 0.72; p < 0.001). Each of the 10 patients who developed new overt bioprosthesis dysfunction during follow-up had evidence of 18F-fluoride uptake at baseline (target-to-background ratio 1.89 [IQR: 1.46 to 2.59]). On multivariable analysis, 18F-fluoride uptake was the only independent predictor of future bioprosthetic dysfunction.Conclusions18F-fluoride PET-CT identifies subclinical bioprosthetic valve degeneration, providing powerful prediction of subsequent valvular dysfunction and highlighting patients at risk of valve failure. This technique holds major promise in the diagnosis of valvular degeneration and the surveillance of patients with bioprosthetic valves. (18F-Fluoride Assessment of Aortic Bioprosthesis Durability and Outcome [18F-FAABULOUS]; NCT02304276)

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Background: Microcalcifications in atherosclerotic plaques are destabilizing, predict adverse cardiovascular events, and are associated with increased morbidity and mortality. 18F-fluoride PET/CT imaging has demonstrated promise as a useful clinical diagnostic tool in identifying high risk plaques; however, there is confusion as to the underlying mechanism of signal amplification seen in PET-positive, CT-negative image regions. This study tested the hypothesis that 18F-fluoride PET/CT can identify early microcalcifications. Methods and Results: 18F-fluoride signal amplification derived from microcalcifications was validated against near infrared fluorescence (NIRF) molecular imaging and histology using an in vitro 3D hydrogel collagen platform, ex vivo human specimens, and a mouse model of atherosclerosis. Microcalcification size correlated inversely with collagen concentration. The 18F-fluoride ligand bound to microcalcifications formed by calcifying vascular smooth muscle cell-derived extracellular vesicles in the in vitro 3D collagen system and exhibited an increasing signal with an increase in collagen concentration (0.25mg/ml collagen - 33.8×102±12.4×102 CPM; 0.5 mg/ml collagen - 67.7×102±37.4×102 CPM, p=0.0014), suggesting amplification of the PET signal by smaller microcalcifications. We further incubated human atherosclerotic endarterectomy specimens with clinically-relevant concentrations of 18F-fluoride. The 18F-fluoride ligand labeled microcalcifications in PET-positive, CT-negative regions of explanted human specimens as evidenced by 18F-fluoride PET/CT imaging, NIRF and histological analysis. Additionally, the 18F-fluoride ligand identified micro- and macrocalcifications in atherosclerotic aortas obtained from LDLr-deficient mice. Conclusions: Our results suggest that 18F-fluoride PET signal in PET-positive, CT-negative regions of human atherosclerotic plaques is the result of developing microcalcifications, and high surface area in regions of small microcalcifications may amplify PET signal.

See Dehay and Bezard (doi:10.1093/brain/awz329) for a scientific commentary on this article. Intrastriatal injections of fibrillar α-synuclein in rodents have been shown to induce a Parkinson’s disease-like spreading of Lewy body pathology. Chu et al. inject exogenous α-synuclein pre-formed fibrils into the putamen of non-human primates, and observe spreading of pathology, nigrostriatal degeneration, and dopamine transporter upregulation indicative of early Parkinson’s disease.

Rationale: Myocardial infarction (MI) is one of the leading causes of death worldwide and inflammation is central to the tissue response and patient outcomes. The 18kDa translocator protein (TSPO) has been utilized in positron emission tomography (PET) as an inflammatory biomarker. The aims of this study were to: 1) screen novel, fluorinated, TSPO radiotracers for susceptibility to the rs6971 genetic polymorphism using in vitro competition binding assays in human brain and heart, 2) assess whether the in vivo characteristics of our lead radiotracer, 18 F-LW223, are suitable for clinical translation and 3) validate whether 18 F-LW223 can detect macrophage driven inflammation in a rat myocardial infarction model. Methods: Fifty-one human brain and twenty-nine human heart tissue samples were screened for the rs6971 polymorphism. Competition binding assays were conducted with 3 H-PK11195 and the following ligands: PK11195, PBR28 and our novel compounds (AB5186 and LW223). Naive rats and mice were used for in vivo PET kinetic studies, radiometabolite studies and dosimetry experiments. Rats underwent permanent coronary artery ligation and were scanned using PET/CT with invasive input function at 7 days following MI. For quantification of PET signal in the hypoperfused myocardium, K 1 was used as a surrogate marker of perfusion to correct the binding potential for impaired radiotracer transfer from plasma to tissue (BP TC). Results: LW223 binding to TSPO was not susceptible to the rs6971 genetic polymorphism in human brain and heart samples. In rodents, 18 F-LW223 displayed a specific uptake consistent with TSPO expression, a slow metabolism in blood (62% of parent at 120 min), a high plasma free fraction of 38.5% and a suitable dosimetry profile Brain Tissue for Binding Assays Heart Tissue for Binding Assays