The effects of the ß1-adrenergic receptor antagonist bisoprolol administration on mirabegron-stimulated human brown adipose tissue thermogenesis.

AIM: Pharmacological stimulation of human brown adipose tissue (BAT) has been hindered by ineffective activation or undesirable off-target effects. Oral administration of the maximal allowable dose of mirabegron (200 mg), a ß3-adrenergic receptor (ß3-AR) agonist, has been effective in stimulating BAT thermogenesis and whole-body energy expenditure. However, this has been accompanied by undesirable cardiovascular effects. Therefore, we hypothesized that combining mirabegron with a ß1-AR antagonist could suppress these unwanted effects and increase the stimulation of the ß3-AR and ß2-AR in BAT. METHODS: We performed a randomized crossover trial (NCT04823442) in 8 lean men. Mirabegron (200 mg) was administered orally with or without the ß1-AR antagonist bisoprolol (10 mg). Dynamic [11C]-acetate and 2-deoxy-2-[18F]fluoro-d-glucose PET/CT scans were performed sequentially after oral administration of mirabegron ± bisoprolol. RESULTS: Compared to room temperature, mirabegron alone increased BAT oxidative metabolism (0.84 ± 0.46 vs. 1.79 ± 0.91 min-1, p = 0.0433), but not when combined with bisoprolol. The metabolic rate of glucose in BAT, measured using [18F]FDG PET, was significantly higher with mirabegron than mirabegron with bisoprolol (24 ± 10 vs. 16 ± 8 nmol/g/min, p = 0.0284). Bisoprolol inhibited the mirabegron-induced increase in systolic blood pressure and heart rate. CONCLUSION: The administration of bisoprolol decreases the adverse cardiovascular effects of mirabegron. However, the provided dose also blunted the mirabegron-stimulated increase in BAT lipolysis, thermogenesis, and glucose uptake. The attenuation in BAT blood flow induced by the large dose of bisoprolol may have limited BAT thermogenesis.

Chemical synthesis of fluorinated and iodinated 17ß-HSD3 inhibitors and evaluation for imaging prostate cancer tumors and tissue biodistribution.

Prostate cancer is the most common cancer among men and the development of new therapeutic agents is needed for its treatment and/or diagnosis. 17ß-hydroxysteroid dehydrogenase type 3 (17ß-HSD3) is involved in the production of androgens, which stimulates the proliferation of prostate cancer cells. Piperazinomethyl-androsterone sulfonamide derivatives were developed as 17ß-HSD3 inhibitors and the concentration of a representative sulfonamide derivative (compound 1) was found to accumulate in prostate tumor tissues relatively to plasma in a mouse xenograft experiment. This finding gives us the opportunity to specifically target the prostate cancer tumors through the development of a radiolabelled version of compound 1 toward targeted molecular radiotherapy or radioimaging diagnosis. The chemical synthesis of fluorinated and iodinated analogs of compound 1 was achieved, leading to a series of compounds with similar levels of inhibition as the initial candidate. From 17ß-HSD3 inhibition activity, molecular modeling and mouse plasma-concentration studies, the most promising compound of this series was selected, its 18F-radiolabelled version (18F-3) synthesized, and imaging/biodistribution studies engaged. When injected in mice, however, 18F-3 uptake in the target tissues (LNCaP[17ß-HSD3] tumors and testicles) was not sufficient to allow their visualization by positron emission tomography. Plasma concentration values of compounds 3-8 administered orally, however, showed that the para-iodo compound 7 is the most metabolically stable and could therefore be an interesting alternative for radiolabelling and radiotreatment.

High-fructose feeding suppresses cold-stimulated brown adipose tissue glucose uptake independently of changes in thermogenesis and the gut microbiome.

Diets rich in added sugars are associated with metabolic diseases, and studies have shown a link between these pathologies and changes in the microbiome. Given the reported associations in animal models between the microbiome and brown adipose tissue (BAT) function, and the alterations in the microbiome induced by high-glucose or high-fructose diets, we investigated the potential causal link between high-glucose or -fructose diets and BAT dysfunction in humans. Primary outcomes are changes in BAT cold-induced thermogenesis and the fecal microbiome (clinicaltrials.gov, NCT03188835). We show that BAT glucose uptake, but not thermogenesis, is impaired by a high-fructose but not high-glucose diet, in the absence of changes in the gastrointestinal microbiome. We conclude that decreased BAT glucose metabolism occurs earlier than other pathophysiological abnormalities during fructose overconsumption in humans. This is a potential confounding factor for studies relying on 18F-FDG to assess BAT thermogenesis.

Total Postprandial Hepatic Nonesterified and Dietary Fatty Acid Uptake Is Increased and Insufficiently Curbed by Adipose Tissue Fatty Acid Trapping in Prediabetes With Overweight.

Excessive lean tissue uptake of fatty acids (FAs) is important in the development of insulin resistance and may be caused by impaired dietary FA (DFA) storage and/or increased nonesterified FA (NEFA) flux from adipose tissue intracellular lipolysis. Cardiac and hepatic total postprandial FA uptake of NEFA+DFA has, however, never been reported in prediabetes with overweight. In this study, 20 individuals with impaired glucose tolerance (IGT) and 19 participants with normal glucose tolerance (NGT) and normal fasting glucose underwent postprandial studies with whole-body positron emission tomography/computed tomography (PET/CT) with oral [18F]fluoro-thia-heptadecanoic acid and dynamic PET/CT with intravenous [11C]palmitate. Hepatic (97 [range 36-215] mmol/6 h vs. 68 [23-132] mmol/6 h, P = 0.03) but not cardiac (11 [range 4-24] mmol/6 h vs. 8 [3-20] mmol/6 h, P = 0.09) uptake of most sources of postprandial FA (NEFA + DFA uptake) integrated over 6 h was higher in IGT versus NGT. DFA accounted for lower fractions of total cardiac (21% [5-47] vs. 25% [9-39], P = 0.08) and hepatic (19% [6-52] vs. 28% [14-50], P = 0.04) uptake in IGT versus NGT. Increased adipose tissue DFA trapping predicted lower hepatic DFA uptake and was associated with higher total cardiac FA uptake. Hence, enhanced adipose tissue DFA trapping in the face of increased postprandial NEFA flux is insufficient to fully curb increased postprandial lean organ FA uptake in prediabetes with overweight (ClinicalTrials.gov; NCT02808182).

18F-4FMFES and 18F-FDG PET/CT in Estrogen Receptor-Positive Endometrial Carcinomas: Preliminary Report.

This article reports the preliminary results of a phase II clinical trial investigating the use of the estrogen receptor (ER)-targeting PET tracer 4-fluoro-11ß-methoxy-16α-18F-fluoroestradiol (18F-4FMFES) and 18F-FDG PET in endometrial cancers. In parallel, noninvasive interventions were attempted to slow progression of 18F-4FMFES metabolites in the intestines to reduce abdominal background uptake. Methods: In an ongoing study, 25 patients who received prior pathologic confirmation of an ER-positive endometrial cancer or endometrial intraepithelial neoplasia agreed to participate in the ongoing clinical trial. Patients were scheduled for 18F-FDG and 18F-4FMFES PET/CT imaging in random order and within 2 wk. Patients were administered either 4 mg of loperamide orally before 18F-4FMFES tracer injection or repeated intravenous injection of 20 mg of hyoscine N-butylbromide during 18F-4FMFES PET/CT. Regions of interest covering the whole abdomen and excluding the liver, bladder, and uterus were drawn for the 18F-4FMFES PET images, and an SUV threshold of more than 4 was applied. The volume of the resulting region was compared between the different interventions to estimate the extent of the intestinal background uptake. Results: Repeated injection of hyoscine N-butylbromide substantially reduced the intestinal background volume, whereas loperamide had a significant but moderate effect. 18F-4FMFES tumor SUVmax ranged from 3.0 to 14.4 (9.4 ± 3.2), whereas 18F-FDG SUVmax ranged from 0 to 22.0 (7.5 ± 5.1). Tumor-to-background ratio was significantly higher for 18F-4FMFES (16.4 ± 5.4) than for 18F-FDG (7.4 ± 4.6). Significant differences were observed between grade 1 and higher-grade tumors concerning 18F-4FMFES uptake and contrast, 18F-FDG uptake, and the 18F-FDG/18F-4FMFES uptake ratio. Conclusion: It is possible to improve 18F-4FMFES abdominal background using hyoscine N-butylbromide. Both 18F-FDG and 18F-4FMFES PET are suitable for detection of ER-positive endometrial cancers, although 18F-4FMFES yielded a better tumor contrast than did 18F-FDG.

Increased postprandial nonesterified fatty acid efflux from adipose tissue in prediabetes is offset by enhanced dietary fatty acid adipose trapping.

The mechanism of increased postprandial nonesterified fatty acid (NEFA) appearance in the circulation in impaired glucose tolerance (IGT) is due to increased adipose tissue lipolysis but could also be contributed to by reduced adipose tissue (AT) dietary fatty acid (DFA) trapping and increased "spillover" into the circulation. Thirty-one subjects with IGT (14 women, 17 men) and 29 with normal glucose tolerance (NGT, 15 women, 14 men) underwent a meal test with oral and intravenous palmitate tracers and the oral [18F]-fluoro-thia-heptadecanoic acid positron emission tomography method. Postprandial palmitate appearance (Rapalmitate) was higher in IGT versus NGT (P < 0.001), driven exclusively by Rapalmitate from obesity-associated increase in intracellular lipolysis (P = 0.01), as Rapalmitate from DFA spillover was not different between the groups (P = 0.19) and visceral AT DFA trapping was even higher in IGT versus NGT (P = 0.02). Plasma glycerol appearance was lower in IGT (P = 0.01), driven down by insulin resistance and increased insulin secretion. Thus, we found higher AT DFA trapping, limiting spillover to lean organs and in part offsetting the increase in Rapalmitate from intracellular lipolysis. Whether similar findings occur in frank diabetes, a condition also characterized by insulin resistance but relative insulin deficiency, requires further investigation (Clinicaltrials.gov: NCT04088344, NCT02808182).NEW & NOTEWORTHY We found higher adipose tissue dietary fatty acid trapping, limiting spillover to lean organs, that in part offsets the increase in appearance rate of palmitate from intracellular lipolysis in prediabetes. These results point to the adaptive nature of adipose tissue trapping and dietary fatty acid spillover as a protective mechanism against excess obesity-related palmitate appearance rate from intracellular adipose tissue lipolysis.

Human Brown Adipocyte Thermogenesis Is Driven by ß2-AR Stimulation.

Stimulation of brown adipose tissue (BAT) thermogenesis in humans has emerged as an attractive target to improve metabolic health. Pharmacological stimulations targeting the ß3-adrenergic receptor (ß3-AR), the adrenergic receptor believed to mediate BAT thermogenesis, have historically performed poorly in human clinical trials. Here we report that, in contrast to rodents, human BAT thermogenesis is not mediated by the stimulation of ß3-AR. Oral administration of the ß3-AR agonist mirabegron only elicited increases in BAT thermogenesis when ingested at the maximal allowable dose. This led to off-target binding to ß1-AR and ß2-AR, thereby increasing cardiovascular responses and white adipose tissue lipolysis, respectively. ADRB2 was co-expressed with UCP1 in human brown adipocytes. Pharmacological stimulation and inhibition of the ß2-AR as well as knockdown of ADRB1, ADRB2, or ADRB3 in human brown adipocytes all confirmed that BAT lipolysis and thermogenesis occur through ß2-AR signaling in humans (ClinicalTrials.govNCT02811289).

Cross-Species Physiological Assessment of Brain Estrogen Receptor Expression Using 18F-FES and 18F-4FMFES PET Imaging.

PURPOSE: A retrospective analysis was performed of preclinical and clinical data acquired during the evaluation of the estrogen receptor (ER) PET tracer 4-fluoro-11ß-methoxy-16α-[18F]-fluoroestradiol (4FMFES) and its comparison with 16α-[18F]-fluoroestradiol (FES) in mice, rats, and humans with a focus on the brain uptake. PROCEDURES: Breast cancer tumor-bearing female BALB/c mice from a previous study and female Sprague-Dawley rats (control and ovariectomized) were imaged by 4FMFES or FES-PET imaging. Immediately after, low-dose CT was performed in the same bed position. Semi-quantitative analysis was conducted to extract %ID/g data. Small cohorts of mice and rats were imaged with 4FMFES in an ultra-high-resolution small animal PET scanner prototype (LabPET II). Rat brains were dissected and imaged separately with both PET and autoradiography. In parallel, 31 breast cancer patients were enrolled in a clinical phase II study to compare 4FMFES with FES for oncological assessment. Since the head was included in the field of view, brain uptake of discernable foci was measured and reported as SUVMax. RESULTS: Regardless of the species studied, 4FMFES and FES uptake were relatively uniform in most regions of the brain, except for bilateral foci at the base of the skull, at the midsection of the brain. Anatomical localization of the PET signal using CT image fusion indicates that the signal origins from the pituitary in all studied species. 4FMFES yielded lower pituitary uptake than FES in patients, but an inverse trend was observed in rodents. 4FMFES pituitary contrast was higher than FES in all assessed groups. High-resolution small animal imaging of the brain of rats and mice revealed a supplemental signal anterior to the pituitary, which is likely to be the medial preoptic area. Dissection data further confirmed those findings and revealed additional signals corresponding to the arcuate and ventromedial nuclei, along with the medial and cortical amygdala. CONCLUSION: 4FMFES allowed visualization of ER expression in the pituitary in humans and two different rodent species with better contrast than FES. Improvement in clinical spatial resolution might allow visualization and analysis of other ER-rich brain areas in humans. Further work is now possible to link 4FMFES pituitary uptake to cognitive functions.

A preclinical PET dual-tracer imaging protocol for ER and HER2 phenotyping in breast cancer xenografts.

BACKGROUND: Nuclear medicine is on the constant search of precision radiopharmaceutical approaches to improve patient management. Although discordant expression of the estrogen receptor (ER) and the human epidermal growth factor receptor 2 (HER2) in breast cancer is a known dilemma for appropriate patient management, traditional tumor sampling is often difficult or impractical. While 2-deoxy-2[18F]fluoro-D-glucose (18F-FDG)-positron emission tomography (PET) is an option to detect subclinical metastases, it does not provide phenotype information. Radiolabeled antibodies are able to specifically target expressed cell surface receptors. However, their long circulating half-lives (days) require labeling with long-lived isotopes, such as 89Zr, in order to allow sufficient time for tracer clearance from the blood compartment and to accumulate adequately in target tumors and, thus, generate high-quality PET images. The aim of this study was to develop a dual-tracer PET imaging approach consisting of a fast-clearing small molecule and a slow-clearing antibody. This approach was evaluated in a model consisting of mice harboring separate breast cancer xenografts with either an ER+/HER2- or ER-/HER2+ phenotype, comparable to human metastatic disease with intertumor heterogeneity. Lastly, the aim of our study was to determine the feasibility of specifically identifying these two important phenotypes in an acceptable time window. METHODS: Female nude mice were subcutaneously implanted on opposite shoulders with the ER+/HER2- and ER-/HER2+ MCF-7 and JIMT-1 tumor cell lines, respectively. A second model was developed consisting of mice implanted orthotopically with either MCF-7 or JIMT-1 cells. Pharmacokinetic analysis, serial PET imaging, and biodistribution were first performed for [89Zr]Zr-DFO-trastuzumab (89Zr-T) up to 8 days post-injection (p.i.) in JIMT-1 bearing mice. Region-of-interest (ROI) and biodistribution-derived uptake (% injected-activity/gram of tissue [%IA/g]) values and tumor-to-background ratios were obtained. Results were compared in order to validate ROI and identify early time points that provided high contrast tumor images. For the dual-tracer approach, cohorts of tumor-bearing mice were then subjected to sequential tracer PET imaging. On day 1, mice were administered 4-fluoro-11ß-methoxy-16α-[18F]-fluoroestradiol (4FMFES) which targets ER and imaged 45 min p.i. This was immediately followed by the injection of 89Zr-T. Mice were then imaged on day 3 or day 7. ROI analysis was performed, and uptake was calculated in tumors and selected healthy organs for all radiotracers. Quality of tumor targeting for all tracers was evaluated by tumor contrast visualization, tumor and normal tissue uptake, and tumor-to-background ratios. RESULTS: 89Zr-T provided sufficiently high tumor and low background uptake values that furnished high contrast tumor images by 48 h p.i. For the dual-tracer approach, 4FMFES provided tumor uptake values that were significantly increased in MCF-7 tumors. When 89Zr-T-PET was combined with 18F-4FMFES-PET, the entire dual-tracer sequential-imaging procedure provided specific high-quality contrast images of ER+/HER2- MCF-7 and ER-/HER2+ JIMT-1 tumors for 4FMFES and 89Zr-T, respectively, as short as 72 h from start to finish. CONCLUSIONS: This protocol can provide high contrast images of tumors expressing ER or HER2 within 3 days from injection of 4FMFES to final scan of 89Zr-T and, hence, provides a basis for future dual-tracer combinations that include antibodies.

Seven-day overfeeding enhances adipose tissue dietary fatty acid storage and decreases myocardial and skeletal muscle dietary fatty acid partitioning in healthy subjects.

Increased myocardial partitioning of dietary fatty acids (DFA) and decreased left ventricular (LV) function is associated with insulin resistance in prediabetes. We hypothesized that enhanced myocardial DFA partitioning and reduced LV function might be induced concomitantly with reduced insulin sensitivity upon a 7-day hypercaloric (+50% in caloric intake), high-saturated fat (~11%energy), and simple carbohydrates (~54%energy) diet (HIGHCAL) versus an isocaloric diet (ISOCAL) with a moderate amount of saturated fat (~8%energy) and carbohydrates (~50%energy). Thirteen healthy subjects (7 men/6 women) underwent HIGHCAL versus ISOCAL in a randomized crossover design, with organ-specific DFA partitioning and LV function measured using the oral 14(R,S)-[18F]fluoro-6-thia-heptadecanoic acid and [11C]acetate positron emission tomography methods at the end of both interventions. HIGHCAL induced a decrease in insulin sensitivity indexes with no significant change in body composition. HIGHCAL led to increased subcutaneous abdominal (+4.2 ± 1.6%, P < 0.04) and thigh (+2.4 ± 1.2%, P < 0.08) adipose tissue storage and reduced cardiac (-0.31 ± 0.11 mean standard uptake value [(SUV), P < 0.03] and skeletal muscle (-0.17 ± 0.08 SUV, P < 0.05) DFA partitioning without change in LV function. We conclude that early increase in adipose tissue DFA storage protects the heart and skeletal muscles from potential deleterious effects of DFA.

Bariatric Surgery Rapidly Decreases Cardiac Dietary Fatty Acid Partitioning and Hepatic Insulin Resistance Through Increased Intra-abdominal Adipose Tissue Storage and Reduced Spillover in Type 2 Diabetes.

Reduced storage of dietary fatty acids (DFAs) in abdominal adipose tissues with enhanced cardiac partitioning has been shown in subjects with type 2 diabetes (T2D) and prediabetes. We measured DFA metabolism and organ partitioning using positron emission tomography with oral and intravenous long-chain fatty acid and glucose tracers during a standard liquid meal in 12 obese subjects with T2D before and 8-12 days after bariatric surgery (sleeve gastrectomy or sleeve gastrectomy and biliopancreatic diversion with duodenal switch). Bariatric surgery reduced cardiac DFA uptake from a median (standard uptake value [SUV]) 1.75 (interquartile range 1.39-2.57) before to 1.09 (1.04-1.53) after surgery (P = 0.01) and systemic DFA spillover from 56.7 mmol before to 24.7 mmol over 6 h after meal intake after surgery (P = 0.01), with a significant increase in intra-abdominal adipose tissue DFA uptake from 0.15 (0.04-0.31] before to 0.49 (0.20-0.59) SUV after surgery (P = 0.008). Hepatic insulin resistance was significantly reduced in close association with increased DFA storage in intra-abdominal adipose tissues (r = -0.79, P = 0.05) and reduced DFA spillover (r = 0.76, P = 0.01). We conclude that bariatric surgery in subjects with T2D rapidly reduces cardiac DFA partitioning and hepatic insulin resistance at least in part through increased intra-abdominal DFA storage and reduced spillover.

Improved Estrogen Receptor Assessment by PET Using the Novel Radiotracer 18F-4FMFES in Estrogen Receptor-Positive Breast Cancer Patients: An Ongoing Phase II Clinical Trial.

After encouraging preclinical and human dosimetry results for the novel estrogen receptor (ER) PET radiotracer 4-fluoro-11ß-methoxy-16α-18F-fluoroestradiol (18F-4FMFES), a phase II clinical trial was initiated to compare the PET imaging diagnostic potential of 18F-4FMFES with that of 16α-18F-fluoroestradiol (18F-FES) in ER-positive (ER+) breast cancer patients. Methods: Patients diagnosed with ER+ breast cancer (n = 31) were recruited for this study, including 6 who underwent mastectomy or axillary node dissection. For each patient, 18F-FES and 18F-4FMFES PET/CT scans were done sequentially (within a week) and in random order. One hour after injection of either radiotracer, a head-to-thigh static scan with a 2-min acquisition per bed position was obtained. Blood samples were taken at different times after injection to assess each tracer metabolism by reverse-phase thin-layer chromatography. The SUVmean of nonspecific tissues and the SUVmax of the tumor were evaluated for each detected lesion, and tumor-to-nonspecific organ ratios were calculated. Results: Blood metabolite analysis 60 min after injection of the tracer showed a 2.5-fold increase in metabolic stability of 18F-4FMFES over 18F-FES. Although for most foci 18F-4FMFES PET had an SUVmax similar to that of 18F-FES PET, tumor contrast improved substantially in all cases. Lower uptake was consistently observed in nonspecific tissues for 18F-4FMFES, notably a 4-fold decrease in blood-pool activity as compared with 18F-FES. Consequently, image quality was considerably improved using 18F-4FMFES, with lower overall background activity. As a result, 18F-4FMFES successfully identified 9 more lesions than 18F-FES. Conclusion: This phase II study with ER+ breast cancer patients showed that 18F-4FMFES PET achieves a lower nonspecific signal and better tumor contrast than 18F-FES PET, resulting in improved diagnostic confidence and lower false-negative diagnoses.

Dietary fatty acid metabolism of brown adipose tissue in cold-acclimated men.

In rodents, brown adipose tissue (BAT) plays an important role in producing heat to defend against the cold and can metabolize large amounts of dietary fatty acids (DFA). The role of BAT in DFA metabolism in humans is unknown. Here we show that mild cold stimulation (18 °C) results in a significantly greater fractional DFA extraction by BAT relative to skeletal muscle and white adipose tissue in non-cold-acclimated men given a standard liquid meal containing the long-chain fatty acid PET tracer, 14(R,S)-[18F]-fluoro-6-thia-heptadecanoic acid (18FTHA). However, the net contribution of BAT to systemic DFA clearance is comparatively small. Despite a 4-week cold acclimation increasing BAT oxidative metabolism 2.6-fold, BAT DFA uptake does not increase further. These findings show that cold-stimulated BAT can contribute to the clearance of DFA from circulation but its contribution is not as significant as the heart, liver, skeletal muscles or white adipose tissues.

Inhibition of Intracellular Triglyceride Lipolysis Suppresses Cold-Induced Brown Adipose Tissue Metabolism and Increases Shivering in Humans.

Indirect evidence from human studies suggests that brown adipose tissue (BAT) thermogenesis is fueled predominantly by fatty acids hydrolyzed from intracellular triglycerides (TGs). However, no direct experimental evidence to support this assumption currently exists in humans. The aim of this study was to determine the role of intracellular TG in BAT thermogenesis, in cold-exposed men. Using positron emission tomography with 11C-acetate and 18F-fluorodeoxyglucose, we showed that oral nicotinic acid (NiAc) administration, an inhibitor of intracellular TG lipolysis, suppressed the cold-induced increase in BAT oxidative metabolism and glucose uptake, despite no difference in BAT blood flow. There was a commensurate increase in shivering intensity and shift toward a greater reliance on glycolytic muscle fibers without modifying total heat production. Together, these findings show that intracellular TG lipolysis is critical for BAT thermogenesis and provides experimental evidence for a reciprocal role of BAT thermogenesis and shivering in cold-induced thermogenesis in humans.

Postprandial fatty acid uptake and adipocyte remodeling in angiotensin type 2 receptor-deficient mice fed a high-fat/high-fructose diet.

The role of the angiotensin type-2 receptor in adipose physiology remains controversial. The aim of the present study was to demonstrate whether genetic angiotensin type-2 receptor-deficiency prevents or worsens metabolic and adipose tissue morphometric changes observed following a 6-week high-fat/high-fructose diet with injection of a small dose of streptozotocin. We compared tissue uptake of nonesterified fatty acid and dietary fatty acid in wild-type and angiotensin type-2 receptor-deficient mice by using the radiotracer 14(R,S)-[(1) (8)F]-fluoro-6-thia-heptadecanoic acid in mice fed a standard or high-fat diet. Postprandial fatty acid uptake in the heart, liver, skeletal muscle, kidney and adipose tissue was increased in wild-type mice after a high-fat diet and in angiotensin type-2 receptor-deficient mice on both standard and high-fat diets. Compared to the wild-type mice, angiotensin type-2 receptor-deficient mice had a lower body weight, an increase in fasting blood glucose and a decrease in plasma insulin and leptin levels. Mice fed a high-fat diet exhibited increased adipocyte size that was prevented by angiotensin type-2 receptor-deficiency. Angiotensin type-2 receptor-deficiency abolished the early hypertrophic adipocyte remodeling induced by a high-fat diet. The small size of adipocytes in the angiotensin type-2 receptor-deficient mice reflects their inability to store lipids and explains the increase in fatty acid uptake in non-adipose tissues. In conclusion, a genetic deletion of the angiotensin type-2 receptor is associated with metabolic dysfunction of white adipose depots, and indicates that adipocyte remodeling occurs before the onset of insulin resistance in the high-fat fed mouse model.

Seven-Day Caloric and Saturated Fat Restriction Increases Myocardial Dietary Fatty Acid Partitioning in Impaired Glucose-Tolerant Subjects.

Subjects with impaired glucose tolerance (IGT) have increased myocardial partitioning of dietary fatty acids (DFAs) with left ventricular dysfunction, both of which are improved by modest weight loss over 1 year induced by lifestyle changes. Here, we determined the effects of a 7-day hypocaloric diet (-500 kcal/day) low in saturated fat (<7% of energy) (LOWCAL study) versus isocaloric with the usual amount saturated fat (∼10% of energy) diet (ISOCAL) on DFA metabolism in subjects with IGT. Organ-specific DFA partitioning and cardiac and hepatic DFA fractional uptake rates were measured in 15 IGT subjects (7 males/8 females) using the oral 14(R,S)-[18F]-fluoro-6-thia-heptadecanoic acid positron emission tomography method after 7 days of an ISOCAL diet versus a LOWCAL diet using a randomized crossover design. The LOWCAL diet led to reductions in weight and postprandial insulin area under the curve. Myocardial DFA partitioning over 6 h was increased after the LOWCAL diet (2.3 ± 0.1 vs. 1.9 ± 0.2 mean standard uptake value, P < 0.04). However, the early (90-120 min) myocardial DFA fractional uptake was unchanged after the LOWCAL diet (0.055 ± 0.025 vs. 0.046 ± 0.009 min(-1), P = 0.7). Liver DFA partitioning was unchanged, but liver fractional uptake of DFA tended to be increased. Very short-term caloric and saturated fat dietary restrictions do not lead to the same changes in organ-specific DFA metabolism as those associated with weight loss in subjects with IGT.

Selective Impairment of Glucose but Not Fatty Acid or Oxidative Metabolism in Brown Adipose Tissue of Subjects With Type 2 Diabetes.

Spontaneous glucose uptake by brown adipose tissue (BAT) is lower in overweight or obese individuals and in diabetes. However, BAT metabolism has not been previously investigated in patients with type 2 diabetes during controlled cold exposure. Using positron emission tomography with (11)C-acetate, (18)F-fluoro-deoxyglucose ((18)FDG), and (18)F-fluoro-thiaheptadecanoic acid ((18)FTHA), a fatty acid tracer, BAT oxidative metabolism and perfusion and glucose and nonesterified fatty acid (NEFA) turnover were determined in men with well-controlled type 2 diabetes and age-matched control subjects under experimental cold exposure designed to minimize shivering. Despite smaller volumes of (18)FDG-positive BAT and lower glucose uptake per volume of BAT compared with young healthy control subjects, cold-induced oxidative metabolism and NEFA uptake per BAT volume and an increase in total body energy expenditure did not differ in patients with type 2 diabetes or their age-matched control subjects. The reduction in (18)FDG-positive BAT volume and BAT glucose clearance were associated with a reduction in BAT radiodensity and perfusion. (18)FDG-positive BAT volume and the cold-induced increase in BAT radiodensity were associated with an increase in systemic NEFA turnover. These results show that cold-induced NEFA uptake and oxidative metabolism are not defective in type 2 diabetes despite reduced glucose uptake per BAT volume and BAT "whitening."

Contributions of white and brown adipose tissues and skeletal muscles to acute cold-induced metabolic responses in healthy men.

KEY POINTS: Both brown adipose tissue (BAT) and skeletal muscle activation contribute to the metabolic response of acute cold exposure in healthy men even under minimal shivering. Activation of adipose tissue intracellular lipolysis is associated with BAT metabolic response upon acute cold exposure in healthy men. Although BAT glucose uptake per volume of tissue is important, the bulk of glucose turnover during cold exposure is mediated by skeletal muscle metabolic activation even when shivering is minimized. ABSTRACT: Cold exposure stimulates the sympathetic nervous system (SNS), triggering the activation of cold-defence responses and mobilizing substrates to fuel the thermogenic processes. Although these processes have been investigated independently, the physiological interaction and coordinated contribution of the tissues involved in producing heat or mobilizing substrates has never been investigated in humans. Using [U-(13)C]-palmitate and [3-(3)H]-glucose tracer methodologies coupled with positron emission tomography using (11)C-acetate and (18)F-fluorodeoxyglucose, we examined the relationship between whole body sympathetically induced white adipose tissue (WAT) lipolysis and brown adipose tissue (BAT) metabolism and mapped the skeletal muscle shivering and metabolic activation pattern during a mild, acute cold exposure designed to minimize shivering response in 12 lean healthy men. Cold-induced increase in whole-body oxygen consumption was not independently associated with BAT volume of activity, BAT oxidative metabolism, or muscle metabolism or shivering intensity, but depended on the sum of responses of these two metabolic tissues. Cold-induced increase in non-esterified fatty acid (NEFA) appearance rate was strongly associated with the volume of metabolically active BAT (r = 0.80, P = 0.005), total BAT oxidative metabolism (r = 0.70, P = 0.004) and BAT glucose uptake (r = 0.80, P = 0.005), but not muscle glucose metabolism. The total glucose uptake was more than one order of magnitude greater in skeletal muscles compared to BAT during cold exposure (674 ± 124 vs. 12 ± 8 µmol min(-1), respectively, P < 0.001). Glucose uptake demonstrated that deeper, centrally located muscles of the neck, back and inner thigh were the greatest contributors of muscle glucose uptake during cold exposure due to their more important shivering response. In summary, these results demonstrate for the first time that the increase in plasma NEFA appearance from WAT lipolysis is closely associated with BAT metabolic activation upon acute cold exposure in healthy men. In humans, muscle glucose utilization during shivering contributes to a much greater extent than BAT to systemic glucose utilization during acute cold exposure.

Effect of Sex and Impaired Glucose Tolerance on Organ-Specific Dietary Fatty Acid Metabolism in Humans.

Oral 14(R,S)-[(18)F]-fluoro-6-thia-heptadecanoic acid was used to determine whether an increase in cardiac dietary fatty acid (DFA) metabolism in impaired glucose tolerance (IGT) is different in men and women. Myocardial DFA partitioning after 6 h was higher in IGT versus control subjects (P = 0.006) in both men (2.14 [95% CI 1.70-2.18] vs. 1.28 standard uptake value [SUV] units [0.80-1.76]) and women (1.95 [1.57-2.33] vs. 1.64 SUV units [1.32-1.96]) without difference between sexes. Myocardial DFA fractional uptake (Ki) between time 90 and 120 min postprandially was also higher in IGT versus control subjects (P < 0.001) in men (0.063 [0.032-0.095] vs. 0.016 min(-1) [0.007-0.025]) and women (0.050 [0.024-0.077] vs. 0.030 min(-1) [0.013-0.047]) without significant sex difference. Men had higher net myocardial DFA uptake between time 90 and 120 min driven by higher chylomicron-triglyceride (TG) levels. IGT-associated increased cardiac DFA partitioning was directly related to obesity in women, whereas it was associated with IGT per se in men. We conclude that early cardiac DFA uptake is higher in men driven by change in postprandial chylomicron-TG level but that increase in 6-h postprandial cardiac DFA partitioning nevertheless occurs with IGT both in men and women.

Improved cardiac function and dietary fatty acid metabolism after modest weight loss in subjects with impaired glucose tolerance.

Using a novel positron emission tomography (PET) method with oral administration of 14(R,S)-[¹8F]-fluoro-6-thia-heptadecanoic acid (¹8FTHA), we recently demonstrated that subjects with impaired glucose tolerance (IGT) display an impairment in cardiac function associated with increased myocardial uptake of dietary fatty acids. Here, we determined whether modest weight loss induced by lifestyle changes might improve these cardiac metabolic and functional abnormalities. Nine participants with IGT, enrolled in a one-year lifestyle intervention trial, were invited to undergo determination of organ-specific postprandial dietary fatty acids partition using the oral ¹8FTHA method, and cardiac function and oxidative metabolic index using PET [¹¹C]acetate kinetics with ECG-gated PET ventriculography before and after the intervention. The intervention resulted in significant weight loss and reduction of waist circumference, with reduced postprandial plasma glucose, insulin, and triglycerides excursion. We observed a significant increase in stroke volume, cardiac output, and left ventricular ejection fraction associated with reduced myocardial oxidative metabolic index and fractional dietary fatty acid uptake. Modest weight loss corrects the exaggerated myocardial channeling of dietary fatty acids and improves myocardial energy substrate metabolism and function in IGT subjects.