Skeletal muscle is the largest organ determining whole-body insulin sensitivity and metabolic homoeostasis. Adaptive changes of skeletal muscle in response to physical activity include adjustments in the production and secretion of muscle-derived bioactive factors, known as myokines, such as myostatin, IL-4, IL-6, IL-7 and IL-15, myonectin, follistatin-like 1 or leukaemia inhibitory factor. These myokines not only act locally in the muscle in an autocrine/paracrine manner, but also are released to the bloodstream as endocrine factors to regulate physiological processes in other tissues. Irisin, derived from the cleavage of FNDC5 protein, constitutes a myokine that induces myogenesis and fat browning (switch of white adipocytes to brown fat-like cells) together with a concomitant increase in energy expenditure. Besides being a target for irisin actions, the adipose tissue also constitutes a production site of FNDC5. Interestingly, irisin secretion from subcutaneous and visceral fat depots is decreased by long-term exercise training and fasting, suggesting a discordant regulation of FNDC5/irisin in skeletal muscle and adipose tissue. Accordingly, our group has recently reported that the adipokine leptin differentially regulates FNDC5/irisin expression in skeletal muscle and fat, confirming the crosstalk between both tissues. Moreover, irisin secretion and function are regulated by other myokines, such as follistatin or myostatin, as well as by other adipokines, including fibroblast growth factor 21 and leptin. Taken together, myokines have emerged as novel molecular mediators of fat browning and their activity can be modulated by adipokines, confirming the crosstalk between skeletal muscle and adipose tissue to regulate thermogenesis and energy expenditure.

Crosstalk between adipokines and myokines in fat browning.

To better understand the role of irisin in humans, we examined the effects of irisin in human primary adipocytes and fresh human subcutaneous white adipose tissue (scWAT). Human primary adipocytes ...

Irisin exerts dual effects on browning and adipogenesis of human white adipocytes.

Background: The energy-burning capacity of brown adipose tissue (BAT) makes it an attractive target for use in anti-obesity therapies. Moreover, due to its ability to oxidize glucose and lipids, BAT activation has been considered a potential therapy to combat type 2 diabetes and atherogenesis. Summary: BAT is mainly regulated by the sympathetic nervous system (SNS); yet, recent findings have shown a group of novel activators that act independently of the stimulation of the SNS such as cardiac natriuretic peptides, irisin, interleukin-6, β-aminoisobutyric acid and fibroblast growth factor 21 that could influence BAT metabolism. Several strategies are being examined to activate and recruit BAT with no side effects. In this review, we postulate that exercise might activate and recruit human BAT through the activation of SNS, heart and skeletal muscle. Key Messages: Epidemiological and well-designed exercise-based randomized controlled studies are needed to clarify if exercise is able to activate BAT in humans.

/pdf/role-of-exercise-in-the-activation-of-brown-adipose-tissue-356in2xdki.pdf

Role of Exercise in the Activation of Brown Adipose Tissue

Medical imaging is a rich source of invaluable information necessary for clinical judgements. However, the analysis of those exams is not a trivial assignment. In recent times, the use of deep learning (DL) techniques, supervised or unsupervised, has been empowered and it is one of the current research key areas in medical image analysis. This paper presents a survey of the use of DL architectures in computer-assisted imaging contexts, attending two different image modalities: the actively studied computed tomography and the under-studied positron emission tomography, as well as the combination of both modalities, which has been an important landmark in several decisions related to numerous diseases. In the making of this review, we analysed over 180 relevant studies, published between 2014 and 2019, that are sectioned by the purpose of the research and the imaging modality type. We conclude by addressing research issues and suggesting future directions for further improvement. To our best knowledge, there is no previous work making a review of this issue.

Using deep learning techniques in medical imaging: a systematic review of applications on CT and PET

Activating brown adipose tissue through exercise (ACTIBATE) in young adults: Rationale, design and methodology.

SummaryObjective
Augmented brown adipose tissue (BAT) mass and activity lead to higher basic metabolic rate which is beneficial against obesity. Our aim was to investigate whether habitual (i.e. usual weekly participation) physical activity is linked with BAT activity and mass in humans, in a group of patients undergoing 18F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) scanning.

Design
Cross-sectional study.

Patients
Forty patients with cancer [26 male; 14 female; age 52·7 ± 17·5; body mass index (BMI) 26·4 ± 4·5].

Measurements
Patients completed the ‘usual week’ form of the International Physical Activity Questionnaire and underwent assessment of BAT activity/mass via 18F-fluorodeoxyglucose PET/CT.

Results
We detected a significant association between habitual physical activity (METs-minute/week) and BAT activity [normalized by body weight (BW) (τ = 0·28, P = 0·02), body surface area (BSA) (τ = 0·29, P = 0·02) and lean body mass (LBM) (τ = 0·38, P = 0·002)]. We also found a significant negative relationship between BMI and BAT activity [normalized by BW (τ = −0·30, P = 0·006), BSA (τ = −0·31, P = 0·004) and LBM (τ = −0·45, P = 0·001)] as well as a significant negative relationship between age and BAT activity [normalized by LBM (τ = −0·28, P = 0·01)]. The results also indicate significant differences between low/moderate/high levels of habitual physical activity and BAT activity (P < 0·05). Moreover, BAT activity was different across the BMI categories (normal/overweight/obese) in both sexes (P < 0·05). Finally, BAT activity was greater in women than in men (P < 0·05).

Conclusions
Increased participation in habitual physical activity is associated with higher BAT activity. Moreover, individuals with normal BMI demonstrate higher BAT activity compared to overweight and obese individuals. Finally, age is inversely linked with BAT activity, while women demonstrate higher BAT activity than men.

Association between habitual physical activity and brown adipose tissue activity in individuals undergoing PET-CT scan

18F-fluorothymidine (18F-FLT) is a radiolabeled thymidine analog that has been reported to help monitor tumor proliferation and has been studied in primary brain tumors; however, knowledge about 18F-FLT positron emission tomography/computed tomography (PET/CT) in metastatic brain lesions is limited. The purpose of this study is to evaluate the performance of 18F-FLT-PET/CT in metastatic brain lesions. A total of 20 PET/CT examinations (33 lesions) were included in the study. Semiquantitative analysis was performed: standard uptake value (SUV) with the utilization of SUVmax, tumor-to-background ratio (T/B), SUVpeak, SUV1cm³, SUV0.5cm³, SUV50%, SUV75%, PV50% (volume × SUV50%), and PV75% (volume × SUV75%) were calculated. Sensitivity, specificity, and accuracy for each parameter were calculated. Optimal cutoff values for each parameter were obtained. Using a receiver operating characteristic (ROC) curve analysis, the optimal cutoff values of SUVmax, T/B, and SUVpeak for discriminating active from non-active lesions were found to be 0.615, 4.21, and 0.425, respectively. In an ROC curve analysis, the area under the curve (AUC) is higher for SUVmax (p-value 0.017) compared to the rest of the parameters, while using optimal cutoff T/B shows the highest sensitivity and accuracy. PVs (proliferation × volumes) did not show any significance in discriminating positive from negative lesions. 18F-FLT-PET/CT can detect active metastatic brain lesions and may be used as a complementary tool. Further investigation should be performed.

https://www.mdpi.com/2075-4418/9/1/17/pdf

Evaluation of the Performance of 18F-Fluorothymidine Positron Emission Tomography/Computed Tomography (18F-FLT-PET/CT) in Metastatic Brain Lesions.

The contribution of positron emission tomography/computed tomography (PET/CT) with 18F-fludeoxyglucose (FDG) in evaluating ovarian cancer recurrence even after a prolonged disease-free interval, and in therapy response is well-described. Calcifications observed in CT, although usually attributed to benign conditions, may actually represent active disease. Such an example of calcified formations is psammoma bodies. We present a case of 56-y. o. patient with ovarian cancer relapse at the supraclavicular area 18 years after complete response and disease-free interval. The patient received chemotherapy and underwent 18F-FDG-PET/CT for the evaluation of treatment response. Both CT corrected and uncorrected PET images showed hypermetabolism in the massively calcified lymph nodes in the neck, mediastinum, axilla and abdomen, indicative of active residual disease.

Hypermetabolic Calcified Lymph Nodes on 18Fludeoxyglucose-Positron Emission Tomography/Computed Tomography in a Case of Treated Ovarian Cancer Recurrence: Residual Disease or Benign Formation?

Hodgkin’s lymphoma (HL) is the most firmly established indication for the use of positron emission tomography with integrated computed tomography (PET/CT) in the field of malignant lymphomas. In routine clinical practice, PET/CT is increasingly used for initial staging and final response assessment irrespectively of stage as well as in early interim (mid-treatment) response assessment, especially in advanced disease. PET/CT is the standard of care, being strongly recommended for baseline staging and final response assessment by the recently published 2014 recommendations [1, 2]. In contrast, the use of PET/CT for the interim evaluation is not recommended yet, despite its strong prognostic significance in intermediate and advanced stages, because data on effective treatment modification are still insufficient [1–4]. Routine follow-up with PET/CT is not recommended in patients who have achieved a PET-negative status after first-line chemotherapy, due to the high false-positive rate [1–4].

PET/CT in Hodgkin Lymphoma

Positron emission tomography (PET) constitutes a relatively novel imaging procedure useful mainly in oncology, but also in cardiology and neurology. PET imaging is based on the detection of annihilation photons produced after positron emission from a radiolabeled tracer, which follows and corresponds to a specific molecular biological or biochemical pathway. Combination with computed tomography (CT) provides both functional and morphological information in one single device.

Roxani Efthymiadou

Papers

Association between habitual physical activity and brown adipose tissue activity in individuals undergoing PET-CT scan

Evaluation of the Performance of 18F-Fluorothymidine Positron Emission Tomography/Computed Tomography (18F-FLT-PET/CT) in Metastatic Brain Lesions.

Hypermetabolic Calcified Lymph Nodes on 18Fludeoxyglucose-Positron Emission Tomography/Computed Tomography in a Case of Treated Ovarian Cancer Recurrence: Residual Disease or Benign Formation?

PET/CT in Hodgkin Lymphoma

General Principles of PET/CT Imaging