Brown fat in breast cancer patients: analysis of serial 18F-FDG PET/CT scans

18F-FDG PET/CT technology for the assessment of brown adipose tissue: an updated review

INTRODUCTION

This review provides an update of 18 F-fluorodeoxyglucose ([18F] FDG) for Brown adipose tissue (BAT) activity quantification, whose role is not completely understood.

AREAS COVERED

We conducted an unstructured search of the literature for any studies employing the [18F] FDG PET in BAT assessment. We explored BAT quantification both in healthy individuals and in different pathologies, after cold exposure and as a metabolic biomarker. The assessment of possible BAT modulators by using [18F] FDG PET is shown. Further PET tracers and novel developments for BAT assessments are also described.

EXPERT OPINION

Further PET tracers and imaging modalities are under investigation, but the [18F] FDG PET is currently the method of choice for the evaluation of BAT and further multicentric trials are needed for a better understanding of the BAT physiopathology, also after cold stimuli. The modulation of BAT activity, assessed by [18F] FDG PET imaging, seems a promising tool for the management of conditions such as obesity and type 2 diabetes. Moreover, an interesting possible correlation of BAT activation with prognostic [18F] FDG PET indices in cancer patients should be assessed with further multicentric trials.

Metabolic crosstalk between thermogenic adipocyte and cancer cell: Dysfunction and therapeutics

As one of the largest endocrine organs with a wide distribution in organisms, adipose tissue secretes multiple adipokines, cytokines, metabolites, and exosomes to promote tumour development. Elaborating the crosstalk between cancer cells and adipocytes provides a tissue-level perspective of cancer progression, which reflects the heterogeneity and complexity of human tumours. Three main types of adipose tissues, white, brown, and beige adipose tissue, have been described. Thermogenic capacity is a prominent characteristic of brown and beige adipocytes. Most studies so far mainly focus on the contribution of white adipocytes to the tumour microenvironment. However, the role of thermogenic adipose tissue in malignant cancer behaviour has been largely overlooked. Recently, emerging evidence suggests that beige/brown adipocytes play a key role in the development and progression of various cancers. This review focuses on the bidirectional communication between tumour cells and thermogenic adipocytes and the therapeutic strategies to disrupt this interaction.

Brown fat activation demonstrated on FDG PET/CT predicts survival outcome

PURPOSE

The purpose of this study was to compare the survival of patients with and without BAT activity on FDG PET/CT.

METHODS

PET/CT exams from 3937 breast cancer patients were retrospectively reviewed for bilateral symmetric elongated FDG activity in the neck and chest, typical of BAT activation. A control group of age-matched (± 1 year) breast cancer patients who underwent PET/CT the same week was also enrolled for comparison. Kaplan-Meier curves of progression-free survival (PFS) and overall survival (OS) for BAT positive patients and the control group were calculated. Further sub-analysis was performed to account for the hormonal changes associated with menopause.

RESULTS

2.0% (80/3937) of the breast cancer patients who underwent PET/CT demonstrated BAT activation, and 80 additional patients were analyzed for comparison as the group without BAT activity. Mean follow-up was 76 months (range 1-225 months). There were 4 recurrences in the BAT group, compared to 12 in the control. The mean PFS for the BAT group was 127 months, which was significantly lower than the mean PFS of 180 months in the control (p = 0.047). Sub-analysis of premenopausal women again showed longer PFS for the BAT group (129 vs. 196 months, p = 0.095) while no difference was found in postmenopausal women (mean 102 vs. 135 months, p = 0.360). Presence of BAT activity was also a significant predictor variable for PFS on Cox regression.

CONCLUSION

Patients with BAT activity showed longer progression-free survival than those without, emphasizing the need for further evaluation of its role in metabolism, treatment response, tumor microenvironment and long-term prognosis.

Body composition dynamics and impact on clinical outcome in gastric and gastro-esophageal junction cancer patients undergoing perioperative chemotherapy with the FLOT protocol

PURPOSE

Perioperative chemotherapy with FLOT constitutes a standard of care approach for locally advanced, resectable gastric or gastro-esophageal junction (GEJ) cancer. We aimed at investigating anthropometric, CT-based and FDG-PET-based body composition parameters and dynamics during this multidisciplinary approach and the impact on clinical outcomes.

METHODS

This retrospective, single-center study was based on medical records and (FDG-PET)-CT images among gastric/GEJ cancer patients undergoing perioperative FLOT chemotherapy.

RESULTS

Between 2016 and 2021, 46 gastric/GEJ cancer patients started perioperative FLOT at our tertiary cancer center (Salzburg, Austria). At a median follow-up of 32 months median PFS was 47.4 months and median OS was not reached. The skeletal muscle index (SMI, cm²/m²) turned out to be the only body composition parameter with a statistically significant decrease during pre-operative FLOT (51.3 versus 48.8 cm²/m², p = 0.02). Neither pre-FLOT body mass index (BMI), nor SMI had an impact on the duration of pre-operative FLOT, the time interval from pre-operative FLOT initiation to surgery, the necessity of pre-operative or post-operative FLOT de-escalation or the likelihood of the start of postoperative chemotherapy. Pre-FLOT BMI (overweight versus normal, HR: 0.11, 95% CI: 0.02-0.65, p = 0.02) and pre-FLOT SMI (sarcopenia versus no sarcopenia, HR: 5.08, 95% CI: 1.27-20.31, p = 0.02) were statistically significantly associated with PFS in the multivariable analysis.

CONCLUSION

The statistically significant SMI loss during pre-operative FLOT and the meaningful impact of baseline SMI and BMI on PFS argue for the implementation of a nutritional screening and support program prior to the initiation of pre-operative FLOT in clinical routine.

Brown adipose tissue (BAT) activation at 18F-FDG PET/CT: correlation with clinicopathological characteristics in breast cancer

Background

There is conflicting results of few published human 18F-FDG PET/CT studies about BAT activation in breast cancer (BC). The aim of the study is to evaluate the association between the levels of BAT metabolic activity detected by 18F-FDG PET/CT and clinicopathological characteristics of a tumor in patients with primary BC.

Results

BAT was activated in 16 out of 157 (10.2%) consecutive female patients with BC who underwent 18F-FDG PET/CT for initial evaluation. The majority of patients (15/16) had bilateral uptake in the supraclavicular regions. The mean values of the highest SUVmax and total metabolic activity (TMA) of activated BAT were 13.3 ± 9.9 and 79.6 ± 45, respectively. Median outdoor temperature was significantly lower in the activated BAT group (P value=0.035). Patients with BAT activation tended to have a lower median primary tumor size and primary SUVmax, but not statistically significant than those without BAT activation. BAT activation was significantly more frequent among younger age groups (14/16) and patients with lower body mass index (BMI) (10/16), but it was insignificantly more frequent among estrogen receptor-positive (ER+), progesterone receptor-positive (PR+), human epidermal growth factor receptor2 negative (HER2-), invasive ductal carcinoma (IDC), grade II, luminal B subtype, high Ki-67 expression level, patients with positive nodal metastasis, and in patients without distant metastasis. TMA was significantly higher among HER2+ patients (P value=0.019), but insignificantly higher among the younger age groups, stages I and II, invasive lobular carcinoma (ILC), grade I, luminal B subtype, ER+, PR−, higher Ki-67 expression level, patients with positive nodal, and distant metastasis. BMI and patient’s age were the significant independent predictor factors for BAT activation on multivariate regression analysis.

Conclusion

BAT activation in young age females is sex hormone-dependent, positively associated with less aggressive molecular subtypes of BC, less frequent in patients with distant metastasis. BAT activation may be a prognostic factor that carries a better prognosis in BC.

Imaging modalities for diagnosis and monitoring of cancer cachexia

Cachexia, a multifactorial wasting syndrome, is highly prevalent among advanced-stage cancer patients. Unlike weight loss in healthy humans, the progressive loss of body weight in cancer cachexia primarily implicates lean body mass, caused by an aberrant metabolism and systemic inflammation. This may lead to disease aggravation, poorer quality of life, and increased mortality. Timely detection is, therefore, crucial, as is the careful monitoring of cancer progression, in an effort to improve management, facilitate individual treatment and minimize disease complications. A detailed analysis of body composition and tissue changes using imaging modalities—that is, computed tomography, magnetic resonance imaging, (¹⁸F) fluoro-2-deoxy-d-glucose (¹⁸FDG) PET and dual-energy X-ray absorptiometry—shows great premise for charting the course of cachexia. Quantitative and qualitative changes to adipose tissue, organs, and muscle compartments, particularly of the trunk and extremities, could present important biomarkers for phenotyping cachexia and determining its onset in patients. In this review, we present and compare the imaging techniques that have been used in the setting of cancer cachexia. Their individual limitations, drawbacks in the face of clinical routine care, and relevance in oncology are also discussed.

Brown Adipose Tissue in Breast Cancer Evaluated by [18F] FDG-PET/CT

PURPOSE

Recently brown adipose tissue (BAT) activation has been proposed to have a possible role in breast cancer. The aim of this study was to evaluate BAT activation in patients with breast cancer and its relationship with molecular characteristics of tumor.

PROCEDURES

The study group comprised 79 patients with histologically proven ductal breast carcinoma (51 ± 13 years). Data on distribution, intensity (SUVmax), and total metabolic activity (TMA) of BAT were obtained from [¹⁸F] FDG-PET/CT. Clinical and biochemical data were obtained from the database.

RESULTS

BAT activation was present in 12 of the 79 patients (15.2 %). Patients with BAT activation were younger and had a lower body mass index (BMI) (p < 0.05 and p < 0.0005, respectively) and showed less frequently metastasis (p < 0.05). No significant differences were found in estrogen receptor (ER), progesterone receptor (PgR), Ki67, grade, and in molecular subtypes. In patients younger than 55 years and with a BMI < 26, no significant differences were observed between patients with and without BAT activation. In the 12 patients with BAT activation, a significant inverse correlation was observed between TMA and BMI (r = - 0.64, p < 0.05). TMA and SUVmax were higher in grade 2 than in grade 3 patients. No significant differences were found in both TMA and SUVmax between patients with and without lymph node metastases. A significant difference in both TMA and SUVmax was observed among different molecular types, with luminal B patients showing higher values.

CONCLUSIONS

In conclusion, the present study suggests a relation between BAT activation and positive known prognostic factor in breast cancer, such as intermediate tumor grade and luminal B cancer type.

Practice and prospects for PET/CT guided interventions

During the past 10 years, performing real-time molecular imaging with positron emission tomography (PET) in combination with computed tomography (CT) during interventional procedures has undergone rapid development. Keeping in mind the interest of the nuclear medicine readers, an update is provided of the current workflows using real-time PET/CT in percutaneous biopsies and tumor ablations. The clinical utility of PET/CT guided biopsies in cancer patients with lung, liver, lymphoma, and bone tumors are reviewed. Several technological developments, including the introduction of new PET tracers and robotic arms as well as opportunities provided through acquiring radioactive biopsy specimens are briefly reviewed.

A systematic review of imaging studies of human brown adipose tissue

Brown adipose tissue (BAT) is involved in energy dissipation and has been linked to weight loss, insulin sensitivity, and reduced risk of atherosclerotic disease. BAT is found most often in the supraclavicular region, as well as mediastinal and paravertebral areas, and it is predominantly seen in young persons. BAT is activated by cold temperature and the sympathetic nervous system. In humans, BAT was initially detected via 2-deoxy-2-[¹⁸ F]fluoro-d-glucose (FDG) positron emission tomography/computed tomography (PET/CT), a high-resolution molecular imaging modality used to identify and stage malignancies. Recent studies have shown that BAT can be localized using conventional imaging modalities, such as CT or magnetic resonance imaging, as well as radiotracers used for single-photon emission CT. In this systematic review, we have summarized the evidence for BAT detection in humans using various imaging techniques.

Brown fat does not cause cachexia in cancer patients: A large retrospective longitudinal FDG-PET/CT cohort study

Background

Brown adipose tissue (BAT) is a specialized form of adipose tissue, able to increase energy expenditure by heat generation in response to various stimuli. Recently, its pathological activation has been implicated in the pathogenesis of cancer cachexia. To establish a causal relationship, we retrospectively investigated the longitudinal changes in BAT and cancer in a large FDG-PET/CT cohort.

Methods

We retrospectively analyzed 13 461 FDG-PET/CT examinations of n = 8 409 patients at our institution from the winter months of 2007–2015. We graded the activation strength of BAT based on the anatomical location of the most caudally activated BAT depot into three tiers, and the stage of the cancer into five general grades. We validated the cancer grading by an interreader analysis and correlation with histopathological stage. Ambient temperature data (seven-day average before the examination) was obtained from a meteorological station close to the hospital. Changes of BAT, cancer, body mass index (BMI) and temperature between the different examinations were examined with Spearman’s test and a mixed linear model for correlation, and with a causal inference algorithm for causality.

Results

We found n = 283 patients with at least two examinations and active BAT in at least one of them. There was no significant interaction between the changes in BAT activation, cancer burden or BMI. Temperature changes exhibited a strong negative correlation with BAT activity (ϱ = -0.57, p<0.00001). These results were confirmed with the mixed linear model. Causal inference revealed a link of Temperature ➜ BAT in all subjects and also of BMI ➜ BAT in subjects who had lost weight and increased cancer burden, but no role of cancer and no causal links of BAT ➜ BMI.

Conclusions

Our data did not confirm the hypothesis that BAT plays a major role in cancer-mediated weight loss. Temperature changes are the main driver of incidental BAT activity on FDG-PET scans.

A decrease in brown adipose tissue activity is associated with weight gain during chemotherapy in early breast cancer patients

Background

A decrease in thermogenesis is suspected to be implicated in the energy expenditure reduction during breast cancer treatment. This study aimed to investigate the impact of chemotherapy on the metabolic activity of brown adipose tissue (BAT) and the link with weight variation.

Methods

This was an ancillary analysis of a multicentre trial involving 109 HER2+ breast cancer patients treated with neoadjuvant chemotherapy. A centralised review of ¹⁸F-FDG uptake intensity (SUV_max) in specific BAT regions (cervical and supraclavicular) was conducted on two PET-CT scans for each patient (before and after the first course of chemotherapy).

Results

Overall, after one course of chemotherapy a significant decrease of 4.4% in ¹⁸F-FDG-uptake intensity was observed. It was not correlated to initial BMI, age or season. During chemotherapy, 10.1% (n = 11) of the patients lost weight (− 7.7 kg ± 3.8 kg; ie, − 9.4% ± 3.7%) and 29.4% (n = 32) gained weight (+ 5.1 kg ± 1.7 kg; ie, + 8.5% ± 2.6%). Among these subgroups, only the patients who had gained weight underwent a significant decrease (13.42%) in ¹⁸F-FDG uptake intensity (p = 0.042).

Conclusion

This study is the first to highlight in a large cohort of patients the negative impact of chemotherapy on brown adipose tissue activity. Weight gain during chemotherapy could thus potentially be explained in part by a decrease in brown adipose tissue activity.

Increased UCP1 expression in the perirenal adipose tissue of patients with renal cell carcinoma

Perirenal adipose tissue (PAT) has been implicated in renal cell carcinoma (RCC). The expression of uncoupling protein 1 (UCP1) is higher in PAT compared with that in back subcutaneous adipose tissue (bSAT). The aim of the present study was to determine UCP1 expression in different parts of PAT and to analyze the correlation between UCP1 expression in PAT and RCC. PAT from the upper and lower renal poles and bSAT samples were collected from 50 patients with RCC (RCC group) and 54 patients with renal cysts (control group) who had undergone renal surgery. Both UCP1 mRNA and protein levels were found to be significantly higher and adipocytes appeared to be smaller in the PAT of the RCC group. Furthermore, the RCC group had more multilocular UCP1-positive adipocytes. UCP1 staining in the PAT was significantly stronger in the RCC group, but there was no significant difference in UCP1 staining in the bSAT between the two groups. Furthermore, Fuhrman grade and T stage were higher in the high UCP1 expression group of RCC patients. In conclusion, high UCP1 expression in the PAT may serve as an indicator of poor prognosis in RCC.

Exposure to Cold Unmasks Potential Biomarkers of Fibromyalgia Syndrome Reflecting Insufficient Sympathetic Responses to Stress

OBJECTIVES

Fibromyalgia syndrome (FMS) is a chronically painful condition whose symptoms are widely reported to be exacerbated by stress. We hypothesized that female patients with FMS differ from pain-free female controls in their sympathetic responses, a fact that may unmask important biomarkers and factors that contribute to the etiology of FMS.

MATERIALS AND METHODS

In a pilot study, blood pressure (BP), skin temperature, thermogenic activity, circulating glucose, and pain sensitivity of 13 individuals with FMS and 11 controls at room temperature (24°C) were compared with that after exposure to cold (19°C).

RESULTS

When measured at 24°C, BP, skin temperature, blood glucose, and brown adipose tissue (BAT) activity, measured using F-fluorodeoxyglucose positron-emission tomography/computed tomography, did not differ between controls and individuals with FMS. However, after cold exposure (19°C), BP and BAT activity increased in controls but not in individuals with FMS; skin temperature on the calf and arm decreased in controls more than in individiuals with FMS; and circulating glucose was lower in individiuals with FMS than in controls. Pain sensitivity did not change during the testing interval in response to cold.

DISCUSSION

The convergence of the effect of cold on 4 relatively simple measures of thermogenic, cardiovascular, and metabolic activity, each regulated by sympathetic activity, strongly indicate that individuals with FMS have impaired sympathetic responses to stress that are observable and highly significant even when measured in extraordinarily small sample populations. If insufficient sympathetic responses to stress are linked to FMS, stress may unmask and maximize these potential clinical biomarkers of FMS and be related to its etiology.

Translational Pharmacology and Physiology of Brown Adipose Tissue in Human Disease and Treatment

Human brown adipose tissue (BAT) is experimentally modeled to better understand the biology of this important metabolic tissue, and also to enable the potential discovery and development of novel therapeutics for obesity and sequelae resulting from the persistent positive energy balance. This chapter focuses on translation into humans of findings and hypotheses generated in nonhuman models of BAT pharmacology. Given the demonstrated challenges of sustainably reducing caloric intake in modern humans, potential solutions to obesity likely lie in increasing energy expenditure. The energy-transforming activities of a single cell in any given tissue can be conceptualized as a flow of chemical energy from energy-rich substrate molecules into energy-expending, endergonic biological work processes through oxidative degradation of organic molecules ingested as nutrients. Despite the relatively tight coupling between metabolic reactions and products, some expended energy is incidentally lost as heat, and in this manner a significant fraction of the energy originally captured from the environment nonproductively transforms into heat rather than into biological work. In human and other mammalian cells, some processes are even completely uncoupled, and therefore purely energy consuming. These molecular and cellular actions sum up at the physiological level to adaptive thermogenesis, the endogenous physiology in which energy is nonproductively released as heat through uncoupling of mitochondria in brown fat and potentially skeletal muscle. Adaptive thermogenesis in mammals occurs in three forms, mostly in skeletal muscle and brown fat: shivering thermogenesis in skeletal muscle, non-shivering thermogenesis in brown fat, and diet-induced thermogenesis in brown fat. At the cellular level, the greatest energy transformations in humans and other eukaryotes occur in the mitochondria, where creating energetic inefficiency by uncoupling the conversion of energy-rich substrate molecules into ATP usable by all three major forms of biological work occurs by two primary means. Basal uncoupling occurs as a passive, general, nonspecific leak down the proton concentration gradient across the membrane in all mitochondria in the human body, a gradient driving a key step in ATP synthesis. Inducible uncoupling, which is the active conduction of protons across gradients through processes catalyzed by proteins, occurs only in select cell types including BAT. Experiments in rodents revealed UCP1 as the primary mammalian molecule accounting for the regulated, inducible uncoupling of BAT, and responsive to both cold and pharmacological stimulation. Cold stimulation of BAT has convincingly translated into humans, and older clinical observations with nonselective 2,4-DNP validate that human BAT's participation in pharmacologically mediated, though nonselective, mitochondrial membrane decoupling can provide increased energy expenditure and corresponding body weight loss. In recent times, however, neither beta-adrenergic antagonism nor unselective sympathomimetic agonism by ephedrine and sibutramine provide convincing evidence that more BAT-selective mechanisms can impact energy balance and subsequently body weight. Although BAT activity correlates with leanness, hypothesis-driven selective β3-adrenergic agonism to activate BAT in humans has only provided robust proof of pharmacologic activation of β-adrenergic receptor signaling, limited proof of the mechanism of increased adaptive thermogenesis, and no convincing evidence that body weight loss through negative energy balance upon BAT activation can be accomplished outside of rodents. None of the five demonstrably β3 selective molecules with sufficient clinical experience to merit review provided significant weight loss in clinical trials (BRL 26830A, TAK 677, L-796568, CL 316,243, and BRL 35135). Broader conclusions regarding the human BAT therapeutic hypothesis are limited by the absence of data from most studies demonstrating specific activation of BAT thermogenesis in most studies. Additionally, more limited data sets with older or less selective β3 agonists also did not provide strong evidence of body weight effects. Encouragingly, β3-adrenergic agonists, catechins, capsinoids, and nutritional extracts, even without robust negative energy balance outcomes, all demonstrated increased total energy expenditure that in some cases could be associated with concomitant activation of BAT, though the absence of body weight loss indicates that in no cases did the magnitude of negative energy balance reach sufficient levels. Glucocorticoid receptor agonists, PPARg agonists, and thyroid hormone receptor agonists all possess defined molecular and cellular pharmacology that preclinical models predicted to be efficacious for negative energy balance and body weight loss, yet their effects on human BAT thermogenesis upon translation were inconsistent with predictions and disappointing. A few new mechanisms are nearing the stage of clinical trials and may yet provide a more quantitatively robust translation from preclinical to human experience with BAT. In conclusion, translation into humans has been demonstrated with BAT molecular pharmacology and cell biology, as well as with physiological response to cold. However, despite pharmacologically mediated, statistically significant elevation in total energy expenditure, translation into biologically meaningful negative energy balance was not achieved, as indicated by the absence of measurable loss of body weight over the duration of a clinical study.

Does the Poly (ADP-Ribose) Polymerase Inhibitor Veliparib Merit Further Study for Cancer-Associated Weight Loss? Observations and Conclusions from Sixty Prospectively Treated Patients

BACKGROUND

More than 80% of patients with advanced cancer develop weight loss. Because preclinical data suggest poly (ADP-ribose) polymerase (PARP) inhibitors can treat this weight loss, this study was undertaken to explore the PARP inhibitor veliparib for this indication.

OBJECTIVE

The current study was undertaken to analyze prospectively gathered data on weight in cancer patients on PARP inhibitors.

DESIGN/SETTING

The current study relied on a previously published, prospectively conducted phase 1 single institution trial that combined veliparib and topotecan (NCT01012817) as antineoplastic therapy for advanced cancer patients. Serial weight data and, when available and clinically relevant, computerized tomography scans were also examined.

MEASUREMENTS

The primary endpoint was 10% or greater weight gain from trial enrollment.

RESULTS

Nearly all 60 patients lost weight over time. Only one patient manifested a 10% or greater gain in weight. However, review of computerized tomography L3 images showed this weight gain was a manifestation of ascites. Four other patients gained 5% of their baseline weight. However, findings in two patients with available radiographs showed no evidence of muscle augmentation.

CONCLUSIONS

The addition of the PARP inhibitor veliparib to chemotherapy does not appear to result in notable weight gain or in weight maintenance in patients with advanced cancer. Interventions other than PARP inhibitors should be considered for the palliation/treatment of cancer-associated weight loss.

Brown fat depots in adult humans remain static in their locations on PET/CT despite changes in seasonality

Active brown adipose tissue (BAT) in humans has been demonstrated through use of positron emission tomography with 2-deoxy-2-(fluorine-18) fluoro-D-glucose integrated with computed tomography (¹⁸F-FDG PET/CT) scans. The aim of our study was to determine whether active human BAT depots shown on ¹⁸F-FDG PET/CT scans remain static in their location over time. This was a retrospective study. Adult human subjects (n = 15) who had had ¹⁸F-FDG PET/CT imaging (n = 38 scans in total) for clinical reasons were included on the basis of ¹⁸F-FDG uptake patterns consistent with BAT activity. For each subject, ¹⁸F-FDG BAT uptake pattern on serial ¹⁸F-FDG PET/CT images was compared to an index ¹⁸F-FDG PET/CT image with the largest demonstrable BAT volume. Object-based colocalization was expressed as Mander's correlation coefficient (where 1 = 100% overlap, 0 = no overlap). Distribution of ¹⁸F-FDG BAT activity over time and across multiple ¹⁸F-FDG BAT scans was equivalent in 60% (n = 9) of the subjects. The degree of consistency in the pattern of ¹⁸F-FDG BAT uptake in each subject over time was greater than expected by chance in 87% (n = 13) of the subjects (pair-wise agreement 75-100%, Fleiss' κ 0.4-1). The degree of BAT colocalization on serial scans was greater than that expected by chance in 93% (n = 14) of the subjects (mean Mander's coefficient 0.81 ± 0.21 [95% CI]). To our knowledge, our study provides the most conclusive evidence to date to support the notion that active BAT depots in humans (volumes and activities of which were measured through use of ¹⁸F-FDG PET/CT scans) remain static in location over sustained periods.

Implication of atypical supraclavicular F18-fluorodeoxyglucose uptake in patients with breast cancer: Association between brown adipose tissue and breast cancer

It has been reported that F18-fluorodeoxyglucose (FDG) uptake in the neck and supraclavicular lesions represents activated brown adipose tissue (BAT). In the present study, the association between BAT activity, detected by FDG-positron emission tomography (PET), and the clinicopathological features of patients with breast cancer was investigated. The cases of 156 consecutive patients with breast cancer who underwent FDG-PET preoperatively were analyzed. The distribution and intensity of atypical FDG uptake in the neck and/or supraclavicular region was reviewed. The intensity was graded as follows: 1, weak; 2, moderate; and 3, intense. Among the 156 patients, 70 (44.9%) exhibited grade 1 intensity, 65 (41.7%) exhibited grade 2 intensity and 21 (13.5%) exhibited grade 3 intensity. The intensity of FDG was significantly associated with human epidermal growth factor receptor 2 (HER2) expression and progesterone expression. Among the 156 patients, 6 (3.8%) had recurrent disease. Multivariate analysis revealed that showing a low grade of atypical FDG uptake was the only independent risk factor of short-term recurrence, and none of the patients with recurrent disease had atypical FDG uptake that may reflect the activation of BAT. These results indicated that the presence of BAT is associated with HER2 expression and the absence of BAT may be a prognostic factor for breast cancer.

Factors influencing brown fat activation in FDG PET/CT: a retrospective analysis of 15,000+ cases

OBJECTIVE

Brown fat can exhibit high uptake of fluorine-18 fludeoxyglucose (¹⁸F-FDG) on positron emission tomography (PET) and interferes with interpretation of the scan. The goal of this study was to identify factors that may influence brown adipose tissue (BAT) activation.

METHODS

A retrospective study of ¹⁸F-FDG PET scans was performed using a database of 15,109 PET/CT reports. BAT activation reported by nuclear medicine physicians and factors influencing BAT activation were gathered. The data were analyzed using in-house software.

RESULTS

The total reported BAT activation was 3.6%. BAT activation was reported significantly more often in patients who were female (p < 0.0001), younger (p < 0.0001), with lower body mass index (p < 0.0001), with lower blood glucose levels (p = 0.01), indicated for breast cancer (p = 0.004), not administered chemotherapy recently before the scan (p < 0.0001) and shown to have BAT activation in a previous scan (p < 0.0001). BAT activation was also reported significantly more for lower outdoor temperatures (p < 0.0001) and for late morning scans than for afternoon (p = 0.005) and early morning (p = 0.001) scans.

CONCLUSION

This retrospective study of 15,109 scans highlights multiple factors contributing to BAT activation on ¹⁸F-FDG PET. The identification of new factors influencing BAT and confirmation of previously identified factors with a larger data set can be used to more accurately identify patients at risk for BAT activation so that prevention strategies can be implemented. Advances in knowledge: This study presents new factors associated with higher incidence of BAT activation, such as time of day, previous BAT activation and breast cancer. Conversely, recent chemotherapy was associated with reduced incidence of BAT activation.

An emerging role for epigenetic regulation of Pgc-1α expression in environmentally stimulated brown adipose thermogenesis

Metabolic disease is a leading cause of death worldwide, and obesity, a central risk factor, is reaching epidemic proportions. Energy expenditure and brown adipose tissue (BAT) thermogenesis are implicated in metabolic disease, and it is becoming evident that impaired BAT activity is regulated by gene/environment interactions. Peroxisome proliferator-activated receptor γ coactivator 1α (Pgc-1α) is a critical regulator of BAT thermogenesis, which is highly inducible by environmental stimuli such as cold and diet. This review focuses on the environmentally mediated epigenetic and transcriptional regulation of Pgc-1α gene expression during BAT thermogenesis. We illustrate interactions between histone modifications and transcription factors at the Pgc-1α promoter that cause BAT Pgc-1α transcription in response to cold. Histone modifications also modulate BAT Pgc-1α transcription in response to nutrients though diet has been less characterized than cold with respect to regulation of Pgc-1α transcription. Pgc-1α DNA methylation and RNA expression were also correlated to indicators of adiposity and glucose homeostasis across numerous human tissues. Although post-translational modification of Pgc-1α protein has been well-characterized across diverse tissues and environments, comparatively little is known of the epigenetic mechanisms regulating Pgc-1α transcription, particularly in BAT thermogenesis.

Imaging human brown adipose tissue under room temperature conditions with (11)C-MRB, a selective norepinephrine transporter PET ligand

INTRODUCTION

Brown adipose tissue (BAT) plays a critical role in adaptive thermogenesis and is tightly regulated by the sympathetic nervous system (SNS). However, current BAT imaging modalities require cold stimulation and are often unreliable to detect BAT in the basal state, at room temperature (RT). We have shown previously that BAT can be detected in rodents under both RT and cold conditions with (11)C-MRB ((S,S)-(11)C-O-methylreboxetine), a highly selective ligand for the norepinephrine transporter (NET). Here, we evaluate this novel approach for BAT detection in adult humans under RT conditions.

METHODS

Ten healthy, Caucasian subjects (5 M: age 24.6±2.6, BMI 21.6±2.7kg/m(2); 5 F: age 25.4±2.1, BMI 22.1±1.0kg/m(2)) underwent (11)C-MRB PET-CT imaging for cervical/supraclavicular BAT under RT and cold-stimulated conditions (RPCM Cool vest; enthalpy 15°C) compared to (18)F-FDG PET-CT imaging. Uptake of (11)C-MRB, was quantified as the distribution volume ratio (DVR) using the occipital cortex as a low NET density reference region. Total body fat and lean body mass were assessed via bioelectrical impedance analysis.

RESULTS

As expected, (18)F-FDG uptake in BAT was difficult to identify at RT but easily detected with cold stimulation (p=0.01). In contrast, BAT (11)C-MRB uptake (also normalized for muscle) was equally evident under both RT and cold conditions (BAT DVR: RT 1.0±0.3 vs. cold 1.1±0.3, p=0.31; BAT/muscle DVR: RT 2.3±0.7 vs. cold 2.5±0.5, p=0.61). Importantly, BAT DVR and BAT/muscle DVR of (11)C-MRB at RT correlated positively with core body temperature (r=0.76, p=0.05 and r=0.92, p=0.004, respectively), a relationship not observed with (18)F-FDG (p=0.63). Furthermore, there were gender differences in (11)C-MRB uptake in response to cold (p=0.03), which reflected significant differences in the change in (11)C-MRB as a function of both body composition and body temperature.

CONCLUSIONS

Unlike (18)F-FDG, the uptake of (11)C-MRB in BAT offers a unique opportunity to investigate the role of BAT in humans under basal, room temperature conditions.

Review of overlap between thermoregulation and pain modulation in fibromyalgia

Fibromyalgia (FM) syndrome is characterized by widespread pain that is exacerbated by cold and stress but relieved by warmth. We review the points along thermal and pain pathways where temperature may influence pain. We also present evidence addressing the possibility that brown adipose tissue activity is linked to the pain of FM given that cold initiates thermogenesis in brown adipose tissue through adrenergic activity, whereas warmth suspends thermogenesis. Although females have a higher incidence of FM and more resting thermogenesis, they are less able to recruit brown adipose tissue in response to chronic stress than males. In addition, conditions that are frequently comorbid with FM compromise brown adipose activity making it less responsive to sympathetic stimulation. This results in lower body temperatures, lower metabolic rates, and lower circulating cortisol/corticosterone in response to stress--characteristics of FM. In the periphery, sympathetic nerves to brown adipose also project to surrounding tissues, including tender points characterizing FM. As a result, the musculoskeletal hyperalgesia associated with conditions such as FM may result from referred pain in the adjacent muscle and skin.

FDG-PET/CT pitfalls in oncological head and neck imaging

OBJECTIVES

Positron emission tomography-computed tomography (PET/CT) with fluorine-18-fluorodeoxy-D-glucose (FDG) has evolved from a research modality to an invaluable tool in head and neck cancer imaging. However, interpretation of FDG PET/CT studies may be difficult due to the inherently complex anatomical landmarks, certain physiological variants and unusual patterns of high FDG uptake in the head and neck. The purpose of this article is to provide a comprehensive approach to key imaging features and interpretation pitfalls of FDG-PET/CT of the head and neck and how to avoid them.

METHODS

We review the pathophysiological mechanisms leading to potentially false-positive and false-negative assessments, and we discuss the complementary use of high-resolution contrast-enhanced head and neck PET/CT (HR HN PET/CT) and additional cross-sectional imaging techniques, including ultrasound (US) and magnetic resonance imaging (MRI).

RESULTS

The commonly encountered false-positive PET/CT interpretation pitfalls are due to high FDG uptake by physiological causes, benign thyroid nodules, unilateral cranial nerve palsy and increased FDG uptake due to inflammation, recent chemoradiotherapy and surgery. False-negative findings are caused by lesion vicinity to structures with high glucose metabolism, obscuration of FDG uptake by dental hardware, inadequate PET scanner resolution and inherent low FDG-avidity of some tumours.

CONCLUSIONS

The interpreting physician must be aware of these unusual patterns of FDG uptake, as well as limitations of PET/CT as a modality, in order to avoid overdiagnosis of benign conditions as malignancy, as well as missing out on actual pathology.

TEACHING POINTS

• Knowledge of key imaging features of physiological and non-physiological FDG uptake is essential for the interpretation of head and neck PET/CT studies. • Precise anatomical evaluation and correlation with contrast-enhanced CT, US or MRI avoid PET/CT misinterpretation. • Awareness of unusual FDG uptake patterns avoids overdiagnosis of benign conditions as malignancy.

A pilot study of FDG PET/CT detects a link between brown adipose tissue and breast cancer

Background

Breast cancer is the second most lethal cancer in women. Understanding biological mechanisms that cause progression of this disease could yield new targets for prevention and treatment. Recent experimental studies suggest that brown adipose tissue (BAT) may play a key role in breast cancer progression. The primary objective for this pilot study was to determine if the prevalence of active BAT in patients with breast cancer is increased compared to cancer patients with other malignancies.

Methods

We retrospectively analyzed data from 96 breast cancer patients who had FDG PET/CT scan for routine staging at the University of Maryland and 96 age- and weight-matched control female patients with other malignancies (predominantly colon cancer) who had undergone FDG PET/CT imaging on the same day. Data on the distribution (bilateral upper neck, supraclavicular and paraspinal regions) and intensity (SUVmax) of active BAT were evaluated by 2 Nuclear Medicine physicians, blinded to the clinical history.

Results

We found sufficient evidence to conclude that based on our sample data the prevalence of active BAT in breast cancer patients’ group is significantly different from that in the control group. The estimated frequency of BAT activity was 3 fold higher in breast cancer patients as compared to controls with other cancers, (16.7% vs. 5.2%, respectively, p = 0.019). When patients were stratified by age in order to determine the possible impact of age related hormonal changes on active BAT among the younger women (≤ 55 years of age), 25.6% breast cancer patients exhibited BAT activity compared to only 2.8% in control women (p = 0.007). In contrast, among the older women (> 55 years of age), the prevalence of active BAT was similar among breast cancer and control women (10.7% vs 6.7%).

Conclusions

In breast cancer patients prevalence of BAT activity on FDGPET/CT is 3-fold greater than in age- and body weight-matched patients with other solid tumor malignancies; this difference is particularly striking among younger women aged < =55. In summary, our retrospective clinical data provide support to pursue prospective clinical and translational studies to further define the role of BAT in breast cancer development and progression.

Autonomic regulation of brown adipose tissue thermogenesis in health and disease: potential clinical applications for altering BAT thermogenesis

From mouse to man, brown adipose tissue (BAT) is a significant source of thermogenesis contributing to the maintenance of the body temperature homeostasis during the challenge of low environmental temperature. In rodents, BAT thermogenesis also contributes to the febrile increase in core temperature during the immune response. BAT sympathetic nerve activity controlling BAT thermogenesis is regulated by CNS neural networks which respond reflexively to thermal afferent signals from cutaneous and body core thermoreceptors, as well as to alterations in the discharge of central neurons with intrinsic thermosensitivity. Superimposed on the core thermoregulatory circuit for the activation of BAT thermogenesis, is the permissive, modulatory influence of central neural networks controlling metabolic aspects of energy homeostasis. The recent confirmation of the presence of BAT in human and its function as an energy consuming organ have stimulated interest in the potential for the pharmacological activation of BAT to reduce adiposity in the obese. In contrast, the inhibition of BAT thermogenesis could facilitate the induction of therapeutic hypothermia for fever reduction or to improve outcomes in stroke or cardiac ischemia by reducing infarct size through a lowering of metabolic oxygen demand. This review summarizes the central circuits for the autonomic control of BAT thermogenesis and highlights the potential clinical relevance of the pharmacological inhibition or activation of BAT thermogenesis.

Brown adipose tissue as an anti-obesity tissue in humans

During the 11th Stock Conference held in Montreal, Quebec, Canada, world-leading experts came together to present and discuss recent developments made in the field of brown adipose tissue biology. Owing to the vast capacity of brown adipose tissue for burning food energy in the process of thermogenesis, and due to demonstrations of its presence in adult humans, there is tremendous interest in targeting brown adipose tissue as an anti-obesity tissue in humans. However, the future of such therapeutic approaches relies on our understanding of the origin, development, recruitment, activation and regulation of brown adipose tissue in humans. As reviewed here, the 11th Stock Conference was organized around these themes to discuss the recent progress made in each aspect, to identify gaps in our current understanding and to further provide a common groundwork that could support collaborative efforts aimed at a future therapy for obesity, based on brown adipose tissue thermogenesis.

Brown adipose tissue in adult humans: a metabolic renaissance

Brown adipose tissue (BAT) plays a key role in energy homeostasis and thermogenesis in animals, conferring protection against diet-induced obesity and hypothermia through the action of uncoupling protein 1 (UCP1). Recent metabolic imaging studies using positron emission tomography computerized tomography (PET-CT) scanning have serendipitously revealed significant depots of BAT in the cervical-supraclavicular regions, demonstrating persistence of BAT beyond infancy. Subsequent cold-stimulated PET-CT studies and direct histological examination of adipose tissues have demonstrated that BAT is highly prevalent in adult humans. BAT activity correlates positively with increment of energy expenditure during cold exposure and negatively with age, body mass index, and fasting glycemia, suggesting regulatory links between BAT, cold-induced thermogenesis, and energy metabolism. Human BAT tissue biopsies express UCP1 and harbor inducible precursors that differentiate into UCP1-expressing adipocytes in vitro. These recent discoveries represent a metabolic renaissance for human adipose biology, overturning previous belief that BAT had no relevance in adult humans. They also have implications for the understanding of the pathogenesis and treatment of obesity and its metabolic sequelae.

Dual time point 2-deoxy-2-[18F]fluoro-D-glucose PET/CT: nodal staging in locally advanced breast cancer

AIM

To assess dual time point 2-deoxy-2-[(18)F]fluoro-D-glucose (18)(F)FDG PET-CT accuracy in nodal staging and in detection of extra-axillary involvement.

MATERIAL AND METHODS

Dual time point [(18)F] FDG PET/CT scan was performed in 75 patients. Visual and semiquantitative assessment of lymph nodes was performed. Semiquantitative measurement of SUV and ROC-analysis were carried out to calculate SUV(max) cut-off value with the best diagnostic performance. Axillary and extra-axillary lymph node chains were evaluated.

RESULTS

Sensitivity and specificity of visual assessment was 87.3% and 75%, respectively. SUV(max) values with the best sensitivity were 0.90 and 0.95 for early and delayed PET, respectively. SUV(max) values with the best specificity were 1.95 and 2.75, respectively. Extra-axillary lymph node involvement was detected in 26.7%.

CONCLUSION

FDG PET/CT detected extra-axillary lymph node involvement in one-fourth of the patients. Semiquantitative lymph node analysis did not show any advantage over the visual evaluation.

Cancer and heterogeneity of obesity: a potential contribution of brown fat

Obesity has lately been drawing additional attention as a potential cancer risk and, with some exceptions as a prognostic factor. As obesity is a complex issue characterized by different variants, mechanisms and manifestations, its role in cancer development is also a complex problem exceeding the basic fact of the fat content rising above certain limits. Therefore, in the present paper obesity is viewed as a heterogeneous entity, which has distinct connections with cancer pathogenesis. Among other issues, emphasis is made on the state of white and brown adipose tissue, in particular the association of specific brown fat features and the so-called white fat browning with the functions of normal and mutated tumor suppressor genes, such as PTEN and BRCA1. These connections are considered from the viewpoint implying the existence of two types of hormonal carcinogenesis and of hormonal mediation of the genetic predisposition to tumor development, and should be accounted for in prevention and treatment of both obesity and cancer.

Relevance of brown adipose tissue in infancy and adolescence

Brown adipose tissue (BAT) was thought to disappear after infancy. Recent findings of BAT in patients undergoing positron emission tomography/computed tomography (PET/CT) have renewed the interest in deciphering the relevance of this tissue in humans. Available data suggest that BAT is more prevalent in children than in adults and that its activation during adolescence is associated with significantly lower gains in weight and adiposity. Data also show that pediatric patients with metabolically active BAT on PET/CT examinations have significantly greater muscle volume than patients without identifiable BAT. Both the activity and the amount of BAT increase during puberty. The magnitude of the increase is higher in boys as compared with girls and is closely related to gains in muscle volume. Hence, concurrent with the gains in skeletal muscle during infancy and puberty, all infants and adolescents accumulate large amounts of BAT. These observations are consistent with in vitro investigations suggesting close interactions between brown adipocytes, white adipocytes, and myocytes. In this review, we discuss the potential role of this tissue in regulating weight and musculoskeletal development in children.

A role of active brown adipose tissue in cancer cachexia?

Until a few years ago, adult humans were not thought to have brown adipose tissue (BAT). Now, this is a rapidly evolving field of research with perspectives in metabolic syndromes such as obesity and new therapies targeting its bio-energetic pathways. White, brown and so-called brite adipose fat seem to be able to trans-differentiate into each other, emphasizing the dynamic nature of fat tissue for metabolism. Human and animal data in cancer cachexia to date provide some evidence for BAT activation, but its quantitative impact on energy expenditure and weight loss is controversial. Prospective clinical studies can address the potential role of BAT in cancer cachexia using ¹⁸F-fluoro- deoxyglucose positron emission tomography-computed tomography scanning, with careful consideration of co-factors such as diet, exposure to the cold, physical activity and body mass index, that all seem to act on BAT recruitment and activity.

Inverse association between brown adipose tissue activation and white adipose tissue accumulation in successfully treated pediatric malignancy

BACKGROUND

Although the accumulation of white adipose tissue (WAT) is a risk factor for disease, brown adipose tissue (BAT) has been suggested to have a protective role against obesity.

OBJECTIVE

We studied whether changes in BAT were related to changes in the amounts of subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) in children treated for malignancy.

DESIGN

We examined the effect of BAT activity on weight, SAT, and VAT in 32 pediatric patients with cancer whose positron emission tomography-computed tomography (PET-CT) scans at diagnosis showed no BAT activity. Changes in weight, SAT, and VAT from diagnosis to remission for children with metabolically active BAT at disease-free follow-up (BAT+) were compared with those in children without visualized BAT when free of disease (BAT-).

RESULTS

Follow-up PET-CT studies (4.7 ± 2.4 mo later) after successful treatment of the cancer showed BAT+ in 19 patients but no active BAT (BAT-) in 13 patients. BAT+ patients, in comparison with BAT- patients, gained significantly less weight (3.3 ± 6.6% compared with 11.0 ± 11.6%; P = 0.02) and had significantly less SAT (18.2 ± 26.5% compared with 67.4 ± 71.7%; P = 0.01) and VAT (22.6 ± 33.5% compared with 131.6 ± 171.8%; P = 0.01) during treatment. Multiple regression analysis indicated that the inverse relations between BAT activation and measures of weight, SAT, and VAT persisted even after age, glucocorticoid treatment, and the season when the PET-CT scans were obtained were accounted for.

CONCLUSION

The activation of BAT in pediatric patients undergoing treatment of malignancy is associated with significantly less adipose accumulation. This trial was registered at clinicaltrials.gov as NCT01517581.

Determinants of physiologic 18F-FDG uptake in brown adipose tissue in sequential PET/CT examinations

PURPOSE

The aim of this study was to assess independent predictors of 2-deoxy-2-[(18)F]fluoro-D-glucose ((18)F-FDG) uptake in brown adipose tissue (BAT) in patients undergoing repeated positron emission tomography (PET)/computed tomography (CT) scans.

PROCEDURES

Eight hundred forty-eight (mean age 50.9 ± 16 years) patients in whom PET/CT scan was repeated (mean interval 5 ± 1.5 months) constituted the study group. (18)F-FDG uptake in characteristic areas of BAT, with CT density of adipose tissue, greater than background soft-tissue activity was considered as evidence of BAT uptake. Both distribution and maximum standardized uptake values (SUVmax) were registered. Clinical and anamnestic data were collected for each patient.

RESULTS

(18)F-FDG uptake in BAT was present in 8.6% patients at first scan. Independent predictors of presence of uptake were age (younger), gender (female), body mass index (lower), and maximum outdoor temperature (lower). Age was the only independent predictor of BAT (18)F-FDG uptake distribution, while SUVmax was related to both age and outdoor temperature. Independent determinants of persistence of BAT (18)F-FDG uptake at second PET/CT were outdoor temperature at time of second scan and extension of metabolically active BAT at first scan.

CONCLUSIONS

Age, body mass index, and outdoor temperature are significant determinants of BAT evidence at (18)F-FDG PET/CT. Moreover, extension of BAT and outdoor temperature are the strongest determinants of persistence of BAT evidence on (18)F-FDG PET/CT in repeated scan.

Control and physiological determinants of sympathetically mediated brown adipose tissue thermogenesis

Brown adipose tissue (BAT) represents a remarkable heat-producing tissue. The thermogenic potential of BAT is conferred by uncoupling protein 1, a protein found uniquely in brown adipocytes. BAT activity and capacity is controlled by the sympathetic nervous system (SNS), which densely innervates brown fat depots. SNS-mediated BAT thermogenesis is essentially governed by hypothalamic and brainstem neurons. BAT activity is also modulated by brain energy balance pathways including the very significant brain melanocortin system, suggesting a genuine involvement of SNS-mediated BAT thermogenesis in energy homeostasis. The use of positron emission tomography/computed tomography scanning has revealed the presence of well-defined BAT depots in the cervical, clavicular, and paraspinal areas in adult humans. The prevalence of these depots is higher in subjects exposed to low temperature and is also higher in women compared to men. Moreover, the prevalence of BAT decreases with age and body fat mass, suggesting that BAT could be involved in energy balance regulation and obesity in humans. This short review summarizes recent progress made in our understanding of the control of SNS-mediated BAT thermogenesis and of the determinants of BAT prevalence or detection in humans.

The relationship between brown adipose tissue activity and neoplastic status: an (18)F-FDG PET/CT study in the tropics

Background

Brown adipose tissue (BAT) has thermogenic potential. For its activation, cold exposure is considered a critical factor though other determinants have also been reported. The purpose of this study was to assess the relationship between neoplastic status and BAT activity by 2-deoxy-2-[18F]fluoro-D-glucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) in people living in the tropics, where the influence of outdoor temperature was low.

Methods

¹⁸F-FDG PET/CT scans were reviewed and the total metabolic activity (TMA) of identified activated BAT quantified. The distribution and TMA of activated BAT were compared between patients with and without a cancer history. The neoplastic status of patients was scored according to their cancer history and ¹⁸F-FDG PET/CT findings. We evaluated the relationships between the TMA of BAT and neoplastic status along with other factors: age, body mass index, fasting blood sugar, gender, and outdoor temperature.

Results

Thirty of 1740 patients had activated BAT. Those with a cancer history had wider BAT distribution (p = 0.043) and a higher TMA (p = 0.028) than those without. A higher neoplastic status score was associated with a higher average TMA. Multivariate analyses showed that neoplastic status was the only factor significantly associated with the TMA of activated BAT (p = 0.016).

Conclusions

Neoplastic status is a critical determinant of BAT activity in patients living in the tropics. More active neoplastic status was associated with more vigorous TMA of BAT.

Functional brown adipose tissue is related to muscle volume in children and adolescents

OBJECTIVE

We examined whether the depiction of brown adipose tissue (BAT) with positron emission tomography/computed tomography (PET/CT) in pediatric patients is associated with anthropometric measures.

STUDY DESIGN

We determined measures of body mass, adiposity, and musculature in 71 children and adolescents who underwent PET/CT examinations and compared patients with and without BAT. We used regression analyses to assess the relation between BAT and anthropometric measures.

RESULTS

A total of 30 patients (42%) had BAT depicted on PET/CT, 10 of 26 girls (38%) and 20 of 45 boys (44%). Compared with patients without functional BAT, patients with BAT had significantly greater neck musculature (1880 ± 908 cm(3) versus 1299 ± 806 cm(3); P = .028 for boys and 1295 ± 586 cm(3) versus 854 ± 392 cm(3); P = .030 for girls) and gluteus musculature (1359 ± 373 cm(3) versus 1061 ± 500 cm(3); P = .032 for boys and 1138 ± 425 cm(3) versus 827 ± 297 cm(3); P = .038 for girls), but no differences in age, body mass index, or measures of subcutaneous fat. With logistic regression analyses, neck and pelvic musculature predicted the presence of BAT independently of age, sex, body size, and season of scan (P = .018 and .009, respectively).

CONCLUSION

Pediatric patients with visualized BAT on PET/CT examinations had significantly greater muscle volume than patients with no visualized BAT.

18F-fluorobenzyl triphenyl phosphonium: a noninvasive sensor of brown adipose tissue thermogenesis

Recent studies have proposed activation of brown adipose tissue (BAT) thermogenesis as a new strategy to combat obesity. Currently, there is no effective noninvasive imaging agent to directly detect unstimulated BAT and quantify the core mechanism of mitochondrial thermogenesis. We investigated an approach to detect BAT depots and monitor thermogenesis using the mitochondria-targeting voltage sensor radiolabeled fluorobenzyltriphenyl phosphonium (FBnTP).

METHODS

(18)F-FBnTP, (14)C-FBnTP, (18)F-FDG, and (99m)Tc-sestamibi uptake in BAT at room temperature (n = 8) and cold-treated (n = 8) Lewis rats was assayed. The effect of the cold condition on (18)F-FBnTP retention in BAT was assessed in 8 treated and 16 control rats. The effect of the noradrenergic inhibitor propranolol on (14)C-FBnTP response to cold stimulation was investigated in an additional 8 treated and 8 control mice.

RESULTS

At room temperature, (18)F-FBnTP accumulated in BAT to an extent similar to that in the heart, second only to the kidney and twice as much as (99m)Tc-sestamibi. Prior exposure to cold (4°C) for 4 h resulted in an 82% decrease of (14)C-FBnTP uptake and an 813% increase of (18)F-FDG uptake in BAT. (99m)Tc-sestamibi uptake was not affected by cold. Administration of (18)F-FBnTP at room temperature 60 min before 120 and 240 min of exposure to cold resulted in marked washout of the tracer from BAT. Propranolol significantly diminished the effect of cold on (14)C-FBnTP and (18)F-FDG uptake into BAT.

CONCLUSION

The intense uptake of (18)F-FBnTP into BAT at room temperature and the response to cold stimulation suggest the unique potential advantage of (18)F-FBnTP not only in detecting unstimulated BAT at high contrast but also in quantifying the mitochondrial thermogenic activity. (18)F-FBnTP PET may serve as a useful technique to assess BAT volume and function.

Implications of nonshivering thermogenesis for energy balance regulation in humans

The incidence of the metabolic syndrome has reached epidemic levels in the Western world. With respect to the energy balance, most attention has been given to reducing energy (food) intake. Increasing energy expenditure is an important alternative strategy. Facultative thermogenesis, which is the increase in energy expenditure in response to cold or diet, may be an effective way to affect the energy balance. The recent identification of functional brown adipose tissue (BAT) in adult humans promoted a renewed interest in nonshivering thermogenesis (NST). The purpose of this review is to highlight the recent insight in NST, general aspects of its regulation, the major tissues involved, and its metabolic consequences. Sustainable NST in adult humans amounts to 15% of the average daily energy expenditure. Calculations based on the limited available literature show that BAT thermogenesis can amount to 5% of the basal metabolic rate. It is likely that at least a substantial part of NST can be attributed to BAT, but it is possible that other tissues contribute to NST. Several studies on mitochondrial uncoupling indicate that skeletal muscle is another potential contributor to facultative thermogenesis in humans. The general and synergistic role of the sympathetic nervous system and the thyroid axis in relation to NST is discussed. Finally, perspectives on BAT and skeletal muscle NST are given.

Effective reduction of brown fat FDG uptake by controlling environmental temperature prior to PET scan: an expanded case series

INTRODUCTION

Brown fat uptake of 2-deoxy-2-[F-18]fluoro-D: -glucose (FDG) on a positron emission tomography (PET) scan may limit the ability to assess for cancer. Previously, Garcia et al. demonstrated in ten patients a significant decrease in brown fat uptake of 2-deoxy-2-[F-18]fluoro-D: -glucose (FDG) after controlling the patient's environmental temperature.

OBJECTIVE

The objective of the current study is to validate the effectiveness of controlled environmental temperature (CET) to reduce physiologic brown fat (BF) FDG uptake on a PET scan in a larger series.

METHOD

A retrospective review was performed from January 2002 to October 2007 of patients who had (1) a pattern of FDG uptake on PET scan consistent with BF, (2) no evidence of cancer by computed tomography in the regions of interest noted below, (3) repeat scan with CET within 4 months of the 1st PET scan, and (4) no use of drugs reported to reduce BF FDG uptake (e.g., benzodiazepine, beta-blockers, reserpine) unless they were used identically prior to and during both studies. The FDG-PET and controlled environmental temperature-positron emission tomography (CET-PET) scans were performed as per protocol. The non-CET and CET-PET images were blinded/randomized, and three physicians assessed three regions (right neck, left neck, and paraspinal area) semiquantitatively using the following scale: "0" (background [bkgd]), 1 + (> bkgd < liver), 2 + (equal to liver), 3 + (> liver). Standard uptake value (SUV) data was recorded. Results were analyzed using a two-tailed t test.

RESULTS

Of 8,640 FDG-PET scans performed, 30 patients (four male, 26 female) met the above criteria. The median age was 36 years (range, 12-60 years). The mean (± 1 standard deviation) of differences in the scores between the two studies for right neck, left neck, and paraspinal regions, respectively, were for reader 1:(2.1 ± 1.37), (1.95 ± 1.43), and (1.85 ± 1.26); reader 2 (2.3 ± 1.40), (1.70 ± 1.13), and (1.77 ± 1.13); reader 3 (2.17 ± 1.17), (2.20 ± 1.18), and (0.50 ± 1.30); for maximum SUV score (3.4 ± 2.9), (3.3 ± 2.9), and (1.77 ± 1.13). All p values were <0.001.

CONCLUSION

In this larger series, CET effectively reduced the false-positive (18)FDG uptake in BF on PET scans without the use of drugs.

Abnormal Mammary Adipose Tissue Environment of Brca1 Mutant Mice Show a Persistent Deposition of Highly Vascularized Multilocular Adipocytes

A major challenge to breast cancer research is the identification of alterations in the architecture and composition of the breast that are associated with breast cancer progression. The aim of the present investigation was to characterize the mammary adipose phenotype from Brca1 mutant mice in the expectation that this would shed light on the role of the mammary tissue environment in the early stages of breast tumorigenesis. We observed that histological sections of mammary tissue from adult Brca1 mutant mice abnormally display small, multilocular adipocytes that are reminiscent of brown adipose tissue (BAT) as compared to wildtype mice. Using a marker for BAT, the uncoupling protein 1 (UCP1), we demonstrated that these multilocular adipose regions in Brca1 mutant mice stain positive for UCP1. Transcriptionally, UCP1 mRNA levels in the Brca1 mutant mice were elevated greater than 50-fold compared to age-matched mammary glands from wildtype mice. Indeed, BAT has characteristics that are favorable for tumor growth, including high vascularity. Therefore, we also demonstrated that the multilocular brown adipose phenotype in the mammary fat pad of Brca1 mutant mice displayed regions of increased vascularity as evidenced by a significant increase in the protein expression of CD31, a marker for angiogenesis. This Brca1 mutant mouse model should provide a physiologically relevant context to determine whether brown adipose tissue can play a role in breast cancer development.