Hypermetabolic mesenteric brown adipose tissue on dual-time point FDG PET/CT in a patient with benign retroperitoneal pheochromocytoma

Impact of estrogens on resting energy expenditure: A systematic review

The fear of weight gain is one of the main reasons for women not to initiate or to early discontinue hormonal contraception or menopausal hormone therapy. Resting energy expenditure is by far the largest component and the most important determinant of total energy expenditure. Given that low resting energy expenditure is a confirmed predictive factor for weight gain and consecutively for the development of obesity, research into the influence of sex steroids on resting energy expenditure is a particularly exciting area. The objective of this systematic review was to evaluate the effects of medication with natural and synthetic estrogens on resting energy expenditure in healthy normal weight and overweight women. Through complex systematic literature searches, a total of 10 studies were identified that investigated the effects of medication with estrogens on resting energy expenditure. Our results demonstrate that estrogen administration increases resting energy expenditure by up to +208 kcal per day in the context of contraception and by up to +222 kcal per day in the context of menopausal hormone therapy, suggesting a preventive effect of circulating estrogen levels and estrogen administration on weight gain and obesity development.

Browning of Mesenteric White Adipose Tissue in Crohn's Disease: A New Pathological Change and Therapeutic Target

BACKROUND

Hypertrophic mesenteric adipose tissue [htMAT] is a distinctive hallmark of Crohn's disease [CD], and it affects enteritis via inflammatory adipokine secretion by dysfunctional white adipocytes. White adipocytes can become beige adipocytes, which are characterized by active lipid consumption and favourable endocrine function, via white adipocyte browning. Our study aimed to determine whether white adipocyte browning occurs in htMAT and its role in CD.

METHODS

White adipocyte browning was examined in MAT samples from CD patients and controls. Human MAT explants and primary mesenteric adipocytes were cultured for in vitro experiments. Mice with 2,4,6-trinitrobenzenesulphonic acid solution [TNBS]-induced colitis were used for in vivo studies. A β3-adrenergic receptor agonist [CL316,243] was used to induce white adipocyte browning, and IL-4/STAT6 signalling was analysed to explore the mechanism underlying the anti-inflammatory activity of beige adipocytes.

RESULTS

White adipocyte browning was observed in htMAT from CD patients, as shown by the appearance of uncoupling protein 1 [UCP1]-positive multilocular [beige] adipocytes with lipid-depleting activity and anti-inflammatory endocrine profiles. Both human MAT and primary mesenteric adipocytes from CD patients and controls could be induced to undergo browning, which increased their lipid-depleting and anti-inflammatory activities in vitro. Inducing MAT browning ameliorated mesenteric hypertrophy and inflammation as well as colitis in TNBS-treated mice in vivo. The anti-inflammatory activity of beige adipocytes was at least partially related to STAT6 signalling activation via the autocrine and paracrine effects of IL-4.

CONCLUSION

White adipocyte browning is a newly identified pathological change in htMAT of CD patients and a possible therapeutic target.

Intracardiac paraganglioma with a cough as the first symptom

BACKGROUND

Cardiac paragangliomas (PGLs) are clinically rare, with hypertension and metabolic changes as the main symptoms. The tumor is highly related to gene mutation, and surgery is presently the effective treatment. Medical history and clinical manifestations of the patient, routine laboratory examinations and imaging examinations, and pathological examination can help the final diagnosis.

CASE PRESENTATION

The present study presents a 31-year-old male patient with a left atrial mass. The initial symptom was cough. Cardiac enlargement was found during the chest X-ray. The follow-up imaging examination revealed a left atrial occupying lesion, and the possibility of malignant occupying lesions was not ruled out. The patient underwent surgical resection of the mass. The final pathological result revealed paraganglioma. The thoracic computed tomography review two months after the operation revealed that the original occupying lesion disappeared, and no new lesion was found.

CONCLUSIONS

Pheochromocytomas and paragangliomas (PPGLs) are a kind of neuroendocrine tumors. PPGLs can cause secondary hypertension, and lead to a series of clinical syndromes, including myocardial injury, metabolic changes, and so on. The occurrence of PPGIs is related to gene mutation. Biochemical detection, imaging examination, and genetic testing can help diagnose. The tumor should be surgically removed as soon as possible after the diagnosis. As a functional tumor, PPGLs should be fully prepared before surgery to avoid anesthesia and huge fluctuations in blood pressure during and after surgery, or the occurrence of fatal hypertensive crisis and intractable hypotension after tumor resection. Adequate preoperative preparation directly affects the prognosis of patients after surgery. Therefore, multidisciplinary cooperation before, during, and after the operation is extremely important.

A neurogenic signature involving monoamine Oxidase-A controls human thermogenic adipose tissue development

Mechanisms that control 'beige/brite' thermogenic adipose tissue development may be harnessed to improve human metabolic health. To define these mechanisms, we developed a species-hybrid model in which human mesenchymal progenitor cells were used to develop white or thermogenic/beige adipose tissue in mice. The hybrid adipose tissue developed distinctive features of human adipose tissue, such as larger adipocyte size, despite its neurovascular architecture being entirely of murine origin. Thermogenic adipose tissue recruited a denser, qualitatively distinct vascular network, differing in genes mapping to circadian rhythm pathways, and denser sympathetic innervation. The enhanced thermogenic neurovascular network was associated with human adipocyte expression of THBS4, TNC, NTRK3, and SPARCL1, which enhance neurogenesis, and decreased expression of MAOA and ACHE, which control neurotransmitter tone. Systemic inhibition of MAOA, which is present in human but absent in mouse adipocytes, induced browning of human but not mouse adipose tissue, revealing the physiological relevance of this pathway. Our results reveal species-specific cell type dependencies controlling the development of thermogenic adipose tissue and point to human adipocyte MAOA as a potential target for metabolic disease therapy.

Pheochromocytoma and Paraganglioma Patients With Poor Survival Often Show Brown Adipose Tissue Activation

CONTEXT

Pheochromocytomas/paragangliomas (PPGLs) are neuroendocrine tumors that can secrete norepinephrine (NE). Brown adipose tissue (BAT) activation is mediated through the action of NE on β-adrenoceptors (β-ARs). In some malignancies, BAT activation is associated with higher cancer activity.

OBJECTIVE

To study the relationship between BAT activation and PPGL clinical outcomes.

DESIGN

A retrospective case-control study that included 342 patients with PPGLs who underwent 18F-fluoro-2-deoxy-D-glucose positron emission tomography-computed tomography (18F-FDG PET/CT) imaging at the National Institutes of Health (NIH). We excluded all patients with parasympathetic tumors and those who underwent 18F-FDG PET/CT after PPGL resection. Scans of 205 patients were reviewed by 2 blinded nuclear medicine physicians; 16 patients had BAT activation on 18F-FDG PET/CT [7.80%; age 27.50 (15.00-45.50) years; 10 female/6 male; body mass index [BMI] 24.90 [19.60-25.35] kg/m2). From the remaining 189 patients, we selected 36 matched controls (age 34.4 [25.4-45.5] years; 21 female/15 male; BMI 25.0 [22.0-26.0] kg/m2).

PRIMARY OUTCOME MEASURE

Overall survival.

RESULTS

The presence of active BAT on 18F-FDG PET/CT was associated with decreased overall survival when compared with the control group (HRz 5.80; 95% CI, 1.05-32.05; P = 0.02). This association remained significant after adjusting for the SDHB mutation. Median plasma NE in the BAT group was higher than the control group [4.65 vs 0.55 times above the upper limit of normal; P < 0.01]. There was a significant association between higher plasma NE levels and mortality in PPGLs in both groups.

CONCLUSIONS

Our findings suggest that the detection of BAT activity in PPGL patients is associated with higher mortality. We suggest that BAT activation could either be reflecting or contributing to a state of increased host stress that may predict poor outcome in metastatic PPGL.

HYPOTHesizing about central comBAT against obesity

The hypothalamus is a brain region in charge of many vital functions. Among them, BAT thermogenesis represents an essential physiological function to maintain body temperature. In the metabolic context, it has now been established that energy expenditure attributed to BAT function can contribute to the energy balance in a substantial extent. Thus, therapeutic interest in this regard has increased in the last years and some studies have shown that BAT function in humans can make a real contribution to improve diabetes and obesity-associated diseases. Nevertheless, how the hypothalamus controls BAT activity is still not fully understood. Despite the fact that much has been known about the mechanisms that regulate BAT activity in recent years, and that the central regulation of thermogenesis offers a very promising target, many questions remain still unsolved. Among them, the possible human application of knowledge obtained from rodent studies, and drug administration strategies able to specifically target the hypothalamus. Here, we review the current knowledge of homeostatic regulation of BAT, including the molecular insights of brown adipocytes, its central control, and its implication in the development of obesity.

Obesity phenotypes: depot-differences in adipose tissue and their clinical implications

Obesity, defined as excess fat mass, increases risks for multiple chronic diseases, such as type 2 diabetes, cardiovascular disease, and several types of cancer. Beyond adiposity per se, the pattern of fat distribution, android or truncal as compared to gynoid or peripheral, has a profound influence on systemic metabolism and hence risk for obesity complications. Not only factors as genetics, environment, gender, and age account for the apparent compartmentalization of white adipose tissue (WAT) in the body. Indeed, the heterogeneity among different anatomical depots also appears to stem from their intrinsic diversity, including cellular developmental origin, proliferative capacity, glucose and lipid metabolism, insulin sensitivity, cytokine pattern, thermogenic ability, and vascularization. Under the obese condition, these depot-specific differences translate into specific WAT distribution patterns, giving rise to different cardiometabolic consequences. This review summarizes the clinical and mechanistic evidence for the depot-specific differences and the phenotypic characteristics of different WAT depots that link their depot-specific biology to obesity-specific complications.

18F-FDG PET/CT of Brown Adipose Tissue Hyperactivation Associated With Pregnancy and Paraganglioma

This 32-year-old woman presented with pregnancy-related arterial hypertension unresponsive to antihypertensive therapy. During cesarean delivery, a lobulated retroperitoneal mass was discovered. F-FDG PET/CT performed 18 days postpartum demonstrated the hyperactive retroperitoneal mass and extensive hyperactivated brown adipose tissue. The mass was surgically removed, revealing a para-aortic multicentric paraganglioma. After surgery, blood pressure normalized, and serum chromogranin A and urinary metanephrines normalized. Brown adipose tissue hypermetabolism disappeared on follow-up FDG PET. Her initial FDG PET demonstrated brown adipose tissue hyperactivation, which may have been caused by the combination of hormonal changes in pregnancy and the paraganglioma.

Convertible visceral fat as a therapeutic target to curb obesity

New therapeutic and preventative strategies are needed to address the growing obesity epidemic. In animal models, brown adipose tissue activation and the associated heat produced contribute to countering obesity and the accompanying metabolic abnormalities. Adult humans also have functional brown fat. Here, we present and discuss the concepts of murine and human white adipose tissue plasticity and the transdifferentiation of white adipocytes into brown adipocytes. Human visceral adipocytes - which are crucial contributors to the burden of obesity and its complications - are particularly susceptible to such transdifferentiation. Therefore, we propose that this process should be a focus of anti-obesity research. Approved drugs that have browning properties as well as future drugs that target molecular pathways involved in white-to-brown visceral adipocyte transdifferentiation may provide new avenues for obesity therapy.

Thermogenic brown and beige/brite adipogenesis in humans

Evidence from rodents established an important role of brown adipose tissue (BAT) in energy expenditure. Moreover, to sustain thermogenesis, BAT has been shown to be a powerful sink for draining and oxidation of glucose and triglycerides from blood. The potential of BAT activity in protection against obesity and metabolic syndrome is recognized. Recently, an unexpected presence and activity of BAT has been found in adult humans. Here we review the most recent research in this field and, specifically, how new findings apply to humans. Moreover, we seek to clarify the underlying biological processes occurring beyond the burst of new nomenclature in the field. The cell type responsible for thermogenesis, the brown adipocyte, arises from complex developmental processes. In addition to 'classical' brown adipocytes, present in developmentally programmed BAT depots, there are brown adipocytes, named 'brite' (from 'brown-in-white') or 'beige', which appear in response to thermogenic stimuli in white fat due to the so-called 'browning' process. Beige/brite cells appear to be important components of BAT depots in adult humans. In addition to the known control of BAT activity by the sympathetic nervous system, metabolic and hormonal signals originating in muscle or liver (e.g. irisin, FGF21) are recognized as activators of BAT and beige/brite adipocytes.

Insights into Brown Adipose Tissue Physiology as Revealed by Imaging Studies

There has been resurgence in interest in brown adipose tissue (BAT) following radiological and histological identification of metabolically active BAT in adult humans. Imaging enables BAT to be studied non-invasively and therefore imaging studies have contributed a significant amount to what is known about BAT function in humans. In this review the current knowledge (derived from imaging studies) about the prevalence, function, activity and regulation of BAT in humans (as well as relevant rodent studies), will be summarized.

18F-FDG PET/CT monitoring of β3 agonist-stimulated brown adipocyte recruitment in white adipose tissue

There is rising interest in recruitment of brown adipocytes into white adipose tissue (WAT) as a means to augment energy expenditure for weight reduction. We thus investigated the potential of (18)F-FDG uptake as an imaging biomarker that can monitor the process of WAT browning.

METHODS

C57BL/6 mice were treated daily with the β3 agonist CL316,243 (5-[(2R)-2-[[(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]-1,3-benzodioxole-2,2-dicarboxylic acid disodium salt), whereas controls received saline. (18)F-FDG small-animal PET/CT was serially performed at 1 h after CL316,243 injection. After sacrifice, interscapular brown adipose tissue (BAT) and WAT depots were extracted, weighed, and measured for (18)F-FDG uptake. Tissues underwent immunostaining, and UCP1 content was quantified by Western blotting.

RESULTS

PET/CT showed low (18)F-FDG uptake in both BAT and inguinal WAT at baseline. BAT uptake was substantially increased by a single stimulation with CL316,243. Uptake in inguinal WAT was only modestly elevated by the first stimulation uptake but gradually increased to BAT level by prolonged stimulation. Ex vivo measurements recapitulated the PET findings, and measured (18)F-FDG uptake in other WAT depots was similar to inguinal WAT. WAT browning by prolonged stimulation was confirmed by a substantial increase in uncoupling protein 1 (UCP1), cytochrome-c oxidase 4 (COX4), and PR domain containing 16 (PRDM16) staining as markers of brown adipocytes. UCP1 content, which served as a measure for extent of browning, was low in baseline inguinal WAT but linearly increased over 10 d of CL316,243 injection. Finally, image-based and ex vivo-measured (18)F-FDG uptake in inguinal WAT correlated well with UCP1 content.

CONCLUSION

(18)F-FDG PET/CT has the capacity to monitor brown adipocyte recruitment into WAT depots in vivo and may thus be useful for screening the efficacy of strategies to promote WAT browning.