Performance Evaluation of a Semi-automated Method for [18F]FDG Uptake in Abdominal Visceral Adipose Tissue

Visceral adipose tissue phenotype and hypoadiponectinemia are associated with aortic Fluorine-18 fluorodeoxyglucose uptake in patients with familial dyslipidemias

BACKGROUND

The role of adipose tissue (AT) in arterial inflammation in familial dyslipidaemias is poorly studied. We investigated the relationship between AT and arterial inflammation in patients with heterozygous familial hypercholesterolemia (heFH) and familial combined hyperlipidemia (FCH).

METHODS AND RESULTS

A total of 40 patients (20 heFH/20 FCH) and a subgroup of 20 of non-heFH/FCH patients were enrolled. Participants underwent blood sampling for serum adipokine measurements and Fluorine-18 fluorodeoxyglucose (18F-FDG) PET/CT imaging. Abdominal visceral (VAT) and subcutaneous (SAT) AT volumes and AT and abdominal aorta 18F-FDG uptake were quantified. FCH patients had increased VAT (pANOVA = 0.004) and SAT volumes (pANOVA = 0.003), lower VAT metabolic activity (pANOVA = 0.0047), and lower adiponectin levels (pANOVA = 0.007) compared to heFH or the control group. Log(Serum adiponectin) levels were correlated with aortic TBR (b = - 0.118, P = 0.038). In mediation analysis, VAT volume was the major determinant of circulating adiponectin, an effect partly mediated via VAT TBR. Clustering of the population of heFH/FCH by VAT volume/TBR and serum adiponectin identified two distinct patient clusters with significant differences in aortic TBR levels (2.11 ± 0.06 vs 1.89 ± 0.05, P= 0.012).

CONCLUSIONS

VAT phenotype (increased VAT volume and/or high VAT TBR) and hypoadiponectinemia may account for the observed differences in arterial inflammation levels between heFH and FCH patients.

[18F]FDG Uptake in Adipose Tissue Is Not Related to Inflammation in Type 2 Diabetes Mellitus

Purpose

2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) uptake is a marker of metabolic activity and is therefore used to measure the inflammatory state of several tissues. This radionuclide marker is transported through the cell membrane via glucose transport proteins (GLUTs). The aim of this study is to investigate whether insulin resistance (IR) or inflammation plays a role in [¹⁸F]FDG uptake in adipose tissue (AT).

Procedures

This study consisted of an in vivo clinical part and an ex vivo mechanistic part. In the clinical part, [¹⁸F]FDG uptake in abdominal visceral AT (VAT) and subcutaneous AT (SAT) was determined using PET/CT imaging in 44 patients with early type 2 diabetes mellitus (T2DM) (age 63 [54–66] years, HbA1c [6.3 ± 0.4 %], HOMA-IR 5.1[3.1–8.5]). Plasma levels were measured with ELISA. In the mechanistic part, AT biopsies obtained from 8 patients were ex vivo incubated with [¹⁸F]FDG followed by autoradiography. Next, a qRT-PCR analysis was performed to determine GLUT and cytokine mRNA expression levels. Immunohistochemistry was performed to determine CD68⁺ macrophage infiltration and GLUT4 protein expression in AT.

Results

In vivo VAT [¹⁸F]FDG uptake in patients with T2DM was inversely correlated with HOMA-IR (r = − 0.32, p = 0.034), and positively related to adiponectin plasma levels (r = 0.43, p = 0.003). Ex vivo [¹⁸F]FDG uptake in VAT was not related to CD68⁺ macrophage infiltration, and IL-1ß and IL-6 mRNA expression levels. Ex vivo VAT [¹⁸F]FDG uptake was positively related to GLUT4 (r = 0.83, p = 0.042), inversely to GLUT3 (r = − 0.83, p = 0.042) and not related to GLUT1 mRNA expression levels.

Conclusions

In vivo [¹⁸F]FDG uptake in VAT from patients with T2DM is positively correlated with adiponectin levels and inversely with IR. Ex vivo [¹⁸F]FDG uptake in AT is associated with GLUT4 expression but not with pro-inflammatory markers. The effect of IR should be taken into account when interpreting data of [¹⁸F]FDG uptake as a marker for AT inflammation.

Electronic supplementary material

The online version of this article (10.1007/s11307-020-01538-0) contains supplementary material, which is available to authorized users.

Characterization of Brown Adipose Tissue in a Diabetic Mouse Model with Spiral Volumetric Optoacoustic Tomography

PURPOSE

Diabetes is associated with a deterioration of the microvasculature in brown adipose tissue (BAT) and with a decrease in its metabolic activity. Multispectral optoacoustic tomography has been recently proposed as a new tool capable of differentiating healthy and diabetic BAT by observing hemoglobin gradients and microvasculature density in cross-sectional (2D) views. We report on the use of spiral volumetric optoacoustic tomography (SVOT) for an improved characterization of BAT.

PROCEDURES

A streptozotocin-induced diabetes model and control mice were scanned with SVOT. Volumetric oxygen saturation (sO₂) as well as total blood volume (TBV) in the subcutaneous interscapular BAT (iBAT) was quantified. Segmentation further enabled separating feeding and draining vessels from the BAT anatomical structure.

RESULTS

Scanning revealed a 46 % decrease in TBV and a 25 % decrease in sO₂ in the diabetic iBAT with respect to the healthy control.

CONCLUSIONS

These results suggest that SVOT may serve as an effective tool for studying the effects of diabetes on BAT. The volumetric optoacoustic imaging probe used for the SVOT scans can be operated in a handheld mode, thus potentially providing a clinical translation route for BAT-related studies with this imaging technology.