Otto Muzik

15O PET Measurement of Blood Flow and Oxygen Consumption in Cold-Activated Human Brown Fat

Although it has been believed that brown adipose tissue (BAT) depots disappear shortly after the perinatal period in humans, PET imaging using the glucose analog 18F-FDG has shown unequivocally the existence of functional BAT in adult humans, suggesting that many humans retain some functional BAT past infancy. The objective of this study was to determine to what extent BAT thermogenesis is activated in adults during cold stress and to establish the relationship between BAT oxidative metabolism and 18F-FDG tracer uptake. Methods: Twenty-five healthy adults (15 women and 10 men; mean age ± SD, 30 ± 7 y) underwent triple-oxygen scans (H215O, C15O, and 15O2) as well as measurements of daily energy expenditure (DEE; kcal/d) both at rest and after exposure to mild cold (15.5°C [60°F]) using indirect calorimetry. The subjects were divided into 2 groups (high BAT and low BAT) based on the presence or absence of 18F-FDG tracer uptake (standardized uptake value [SUV] > 2) in cervical–supraclavicular BAT. Blood flow and oxygen extraction fraction (OEF) were calculated from dynamic PET scans at the location of BAT, muscle, and white adipose tissue. Regional blood oxygen saturation was determined by near-infrared spectroscopy. The total energy expenditure during rest and mild cold stress was measured by indirect calorimetry. Tissue-level metabolic rate of oxygen (MRO2) in BAT was determined and used to calculate the contribution of activated BAT to DEE. Results: The mass of activated BAT was 59.1 ± 17.5 g (range, 32–85 g) in the high-BAT group (8 women and 1 man; mean age, 29.6 ± 5.5 y) and 2.2 ± 3.6 g (range, 0–9.3 g) in the low-BAT group (9 men and 7 women; mean age, 31.4 ± 10 y). Corresponding maximal SUVs were significantly higher in the high-BAT group than in the low-BAT group (10.7 ± 3.9 vs. 2.1 ± 0.7, P = 0.01). Blood flow values were significantly higher in the high-BAT group than in the low-BAT group for BAT (12.9 ± 4.1 vs. 5.9 ± 2.2 mL/100 g/min, P = 0.03) and white adipose tissue (7.2 ± 3.4 vs. 5.7 ± 2.3 mL/100 g/min, P = 0.03) but were similar for muscle (4.4 ± 1.9 vs. 3.9 ± 1.7 mL/100 g/min). Moreover, OEF in BAT was similar in the 2 groups (0.51 ± 0.17 in high-BAT group vs. 0.47 ± 0.18 in low-BAT group, P = 0.39). During mild cold stress, calculated MRO2 values in BAT increased from 0.97 ± 0.53 to 1.42 ± 0.68 mL/100 g/min (P = 0.04) in the high-BAT group and were significantly higher than those determined in the low-BAT group (0.40 ± 0.28 vs. 0.51 ± 0.23, P = 0.67). The increase in DEE associated with BAT oxidative metabolism was highly variable in the high-BAT group, with an average of 3.2 ± 2.4 kcal/d (range, 1.9–4.6 kcal/d) at rest, and increased to 6.3 ± 3.5 kcal/d (range, 4.0–9.9 kcal/d) during exposure to mild cold. Although BAT accounted for only a small fraction of the cold-induced increase in DEE, such increases were not observed in subjects lacking BAT. Conclusion: Mild cold-induced thermogenesis in BAT accounts for 15–25 kcal/d in subjects with relatively large BAT depots. Thus, although the presence of active BAT is correlated with cold-induced energy expenditure, direct measurement of MRO2 indicates that BAT is a minor source of thermogenesis in humans.

Assessment of oxidative metabolism in brown fat using PET imaging.

Objective: Although it has been believed that brown adipose tissue (BAT) depots disappear shortly after the perinatal period in humans, positron emission tomography (PET) imaging using the glucose analog 18F-deoxy-d-glucose (FDG) has shown unequivocally the existence of functional BAT in humans, suggesting that most humans have some functional BAT. The objective of this study was to determine, using dynamic oxygen-15 (15O) PET imaging, to what extent BAT thermogenesis is activated in adults during cold stress and to establish the relationship between BAT oxidative metabolism and FDG tracer uptake. Methods: Fourteen adult normal subjects (9F/5M, 30u2009±u20097u2009years) underwent triple oxygen scans (H215O, C15O, 15O2) as well as indirect calorimetric measurements at both rest and following exposure to mild cold (16°C). Subjects were divided into two groups (BAT+ and BAT−) based on the presence or absence of FDG tracer uptake (SUVu2009>u20092) in cervical–supraclavicular BAT. Blood flow and oxygen extraction fraction (OEF) was calculated from dynamic PET scans at the location of BAT, muscle, and white adipose tissue (WAT). The metabolic rate of oxygen (MRO2) in BAT was determined and used to calculate the contribution of activated BAT to daily energy expenditure (DEE). Results: The median mass of activated BAT in the BAT+ group (5F, age 31u2009±u20098) was 52.4u2009g (range 14–68u2009g) and was 1.7u2009g (range 0–6.3u2009g) in the BAT − group (5M/4F, age 29u2009±u20096). Corresponding SUV values were significantly higher in the BAT+ as compared to the BAT− group (7.4u2009±u20093.7 vs. 1.9u2009±u20090.9; pu2009=u20090.03). Blood flow values in BAT were significantly higher in the BAT+ group as compared to the BAT− group (13.1u2009±u20094.4 vs. 5.7u2009±u20091.1u2009ml/100u2009g/min, pu2009=u20090.03), but were similar in WAT (4.1u2009±u20091.6 vs. 4.2u2009±u20091.8u2009ml/100u2009g/min) and muscle (3.7u2009±u20090.8 vs. 3.3u2009±u20091.2u2009ml/100u2009g/min). Moreover, OEF in BAT was similar in the two groups (0.56u2009±u20090.18 in BAT+ vs. 0.46u2009±u20090.19 in BAT−, pu2009=u20090.39). Calculated MRO2 values in BAT increased from 0.95u2009±u20090.74 to 1.62u2009±u20090.82u2009ml/100u2009g/min in the BAT+ group and were significantly higher than those determined in the BAT− group (0.43u2009±u20090.27 vs. 0.56u2009±u20090.24, pu2009=u20090.67). The DEE associated with BAT oxidative metabolism was highly variable in the BAT+ group, with an average of 5.5u2009±u20096.4u2009kcal/day (range 0.57–15.3u2009kcal/day). Conclusion: BAT thermogenesis in humans accounts for less than 20u2009kcal/day during moderate cold stress, even in subjects with relatively large BAT depots. Furthermore, due to the large differences in blood flow and glucose metabolic rates in BAT between humans and rodents, the application of rodent data to humans is problematic and needs careful evaluation.

Evaluation of age-related changes in translocator protein (TSPO) in human brain using 11C-[R]-PK11195 PET

BackgroundWe studied the distribution and expression of translocator protein in the human brain using 11C-[R]-PK-11195 positron emission tomography (PK11195 PET) and evaluated age-related changes.MethodsA dynamic PK11195 PET scan was performed in 15 normal healthy adults (mean age: 29u2009±8.5 years (range: 20 to 49); 7 males) and 10 children (mean age: 8.8u2009±5.2 years (range: 1.2 to 17); 5 males), who were studied for potential neuroinflammation but showed no focally increased PK11195 binding. The PET images were evaluated by calculating standard uptake values and regional binding potential, based on a simplified reference region model, as well as with a voxel-wise analysis using statistical parametric mapping.ResultsPK11195 uptake in the brain is relatively low, compared with the subcortical structures, and symmetrical. The overall pattern of PK11195 distribution in the brain does not change with age. PK11195 uptake was lowest in the frontal-parietal-temporal cortex and highest in the pituitary gland, midbrain, thalamus, basal ganglia, occipital cortex, hippocampus and cerebellum, in descending order. White matter showed negligible PK11195 uptake. Overall, brain PK11195 uptake increased with age, with midbrain and thalamus showing relatively higher increases with age compared with other brain regions.ConclusionsThe brain shows low PK11195 uptake, which is lower in the cortex and cerebellum compared with subcortical structures, suggesting a low level of translocator protein expression. There is no hemispheric asymmetry in PK11195 uptake and the overall pattern of PK11195 distribution in the brain does not change with age. However, brain PK11195 uptake increases with age, with the thalamus and midbrain showing relatively higher increases compared with other brain regions. This increase in uptake suggests an age-related increase in translocator protein expression or the number of cells expressing these receptors or both.

Positron Emission Tomography of Copper Metabolism in the Atp7b−/− Knock-out Mouse Model of Wilson’s Disease

PurposeThis study aims to determine feasibility and utility of copper-64(II) chloride (64CuCl2) as a tracer for positron emission tomography (PET) of copper metabolism imbalance in human Wilson’s disease (WD).ProceduresAtp7b−/− mice, a mouse model of human WD, were injected with 64CuCl2 intravenously and subjected to PET scanning using a hybrid PET-CT (computerized tomography) scanner, with the wild-type C57BL mice as a normal control. Quantitative PET analysis was performed to determine biodistribution of 64Cu radioactivity and radiation dosimetry estimates of 64Cu were calculated for PET of copper metabolism in humans.ResultsDynamic PET analysis revealed increased accumulation and markedly reduced clearance of 64Cu from the liver of the Atp7b−/− mice, compared to hepatic uptake and clearance of 64Cu in the wild-type C57BL mice. Kinetics of copper clearance and retention was also altered for kidneys, heart, and lungs in the Atp7b−/− mice. Based on biodistribution of 64Cu in wild-type C57BL mice, radiation dosimetry estimates of 64Cu in normal human subjects were obtained, showing an effective dose (ED) of 32.2xa0μ (micro)Sv/MBq (weighted dose over 22 organs) and the small intestine as the critical organ for radiation dose (61xa0μGy/MBq for males and 69xa0μGy/MBq for females). Radiation dosimetry estimates for the patients with WD, based on biodistribution of 64Cu in the Atp7b−/− mice, showed a similar ED of 32.8xa0μ (micro)Sv/MBq (pu2009=u20090.53), with the liver as the critical organ for radiation dose (120xa0μSv/MBq for male and 161xa0μSv/MBq for female).ConclusionsQuantitative PET analysis demonstrates abnormal copper metabolism in the mouse model of WD with improved time–resolution. Human radiation dosimetry estimates obtained in this preclinical study encourage direct radiation dosimetry of 64CuCl2 in human subjects. The results suggest feasibility of utilizing 64CuCl2 as a tracer for noninvasive assessment of copper metabolism in WD with PET.

Urinary Copper Elevation in a Mouse Model of Wilson's Disease Is a Regulated Process to Specifically Decrease the Hepatic Copper Load

Body copper homeostasis is regulated by the liver, which removes excess copper via bile. In Wilsons disease (WD), this function is disrupted due to inactivation of the copper transporter ATP7B resulting in hepatic copper overload. High urinary copper is a diagnostic feature of WD linked to liver malfunction; the mechanism behind urinary copper elevation is not fully understood. Using Positron Emission Tomography-Computed Tomography (PET-CT) imaging of live Atp7b−/− mice at different stages of disease, a longitudinal metal analysis, and characterization of copper-binding molecules, we show that urinary copper elevation is a specific regulatory process mediated by distinct molecules. PET-CT and atomic absorption spectroscopy directly demonstrate an age-dependent decrease in the capacity of Atp7b−/− livers to accumulate copper, concomitant with an increase in urinary copper. This reciprocal relationship is specific for copper, indicating that cell necrosis is not the primary cause for the initial phase of metal elevation in the urine. Instead, the urinary copper increase is associated with the down-regulation of the copper-transporter Ctr1 in the liver and appearance of a 2 kDa Small Copper Carrier, SCC, in the urine. SCC is also elevated in the urine of the liver-specific Ctr1 −/− knockouts, which have normal ATP7B function, suggesting that SCC is a normal metabolite carrying copper in the serum. In agreement with this hypothesis, partially purified SCC-Cu competes with free copper for uptake by Ctr1. Thus, hepatic down-regulation of Ctr1 allows switching to an SCC-mediated removal of copper via kidney when liver function is impaired. These results demonstrate that the body regulates copper export through more than one mechanism; better understanding of urinary copper excretion may contribute to an improved diagnosis and monitoring of WD.

Tryptophan metabolism in breast cancers: molecular imaging and immunohistochemistry studies

INTRODUCTIONnTryptophan oxidation via the kynurenine pathway is an important mechanism of tumoral immunoresistance. Increased tryptophan metabolism via the serotonin pathway has been linked to malignant progression in breast cancer. In this study, we combined quantitative positron emission tomography (PET) with tumor immunohistochemistry to analyze tryptophan transport and metabolism in breast cancer.nnnMETHODSnDynamic α-[(11)C]methyl-l-tryptophan (AMT) PET was performed in nine women with stage II-IV breast cancer. PET tracer kinetic modeling was performed in all tumors. Expression of L-type amino acid transporter 1 (LAT1), indoleamine 2,3-dioxygenase (IDO; the initial and rate-limiting enzyme of the kynurenine pathway) and tryptophan hydroxylase 1 (TPH1; the initial enzyme of the serotonin pathway) was assessed by immunostaining of resected tumor specimens.nnnRESULTSnTumor AMT uptake peaked at 5-20 min postinjection in seven tumors; the other two cases showed protracted tracer accumulation. Tumor standardized uptake values (SUVs) varied widely (2.6-9.8) and showed a strong positive correlation with volume of distribution values derived from kinetic analysis (P<.01). Invasive ductal carcinomas (n=6) showed particularly high AMT SUVs (range, 4.7-9.8). Moderate to strong immunostaining for LAT1, IDO and TPH1 was detected in most tumor cells.nnnCONCLUSIONSnBreast cancers show differential tryptophan kinetics on dynamic PET. SUVs measured 5-20 min postinjection reflect reasonably the tracers volume of distribution. Further studies are warranted to determine if in vivo AMT accumulation in these tumors is related to tryptophan metabolism via the kynurenine and serotonin pathways.

Evaluating the arcuate fasciculus with combined diffusion-weighted MRI tractography and electrocorticography

The conventional model of language‐related brain structure describing the arcuate fasciculus as a key white matter tract providing a direct connection between Wernickes region and Brocas area has been called into question. Specifically, the inferior precentral gyrus, possessing both primary motor (Brodmann Area [BA] 4) and premotor cortex (BA 6), has been identified as a potential alternative termination. The authors initially localized cortical sites involved in language using measurement of event‐related gamma‐activity on electrocorticography (ECoG). The authors then determined whether language‐related sites of the temporal lobe were connected, via white matter structures, to the inferior frontal gyrus more tightly than to the precentral gyrus. The authors found that language‐related sites of the temporal lobe were far more likely to be directly connected to the inferior precentral gyrus through the arcuate fasciculus. Furthermore, tractography was a significant predictor of frontal language‐related ECoG findings. Analysis of an interaction between anatomy and tractography in this model revealed tractrography to have the highest predictive value for language‐related ECoG findings of the precentral gyrus. This study failed to support the conventional model of language‐related brain structure. More feasible models should include the inferior precentral gyrus as a termination of the arcuate fasciculus. The exact functional significance of direct connectivity between temporal language‐related sites and the precentral gyrus requires further study. Hum Brain Mapp 35:2333–2347, 2014.

Evaluating reverse speech as a control task with language-related gamma activity on electrocorticography

Reverse speech has often been used as a control task in brain-mapping studies of language utilizing various non-invasive modalities. The rationale is that reverse speech is comparable to forward speech in terms of auditory characteristics, while omitting the linguistic components. Thus, it may control for non-language auditory functions. This finds some support in fMRI studies indicating that reverse speech resulted in less blood-oxygen-level-dependent (BOLD) signal intensity in perisylvian regions than forward speech. We attempted to externally validate a reverse speech control task using intracranial electrocorticography (ECoG) in eight patients with intractable focal epilepsy. We studied adolescent and adult patients who underwent extraoperative ECoG prior to resective epilepsy surgery. All patients received an auditory language task during ECoG recording. Patients were presented 115 audible question stimuli, including 30 reverse speech trials. Reverse speech trials more strongly engaged bilateral superior temporal sites than did the corresponding forward speech trials. Forward speech trials elicited larger gamma-augmentation at frontal lobe sites not attributable to sensorimotor function. Other temporal and frontal sites of significant augmentation showed no significant difference between reverse and forward speech. Thus, we failed to validate reported evidence of weaker activation of temporal neocortices during reverse compared to forward speech. Superior temporal lobe engagement may indicate increased attention to reverse speech. Reverse speech does not appear to be a suitable task for the control of non-language auditory functions on ECoG.

Differentiation of Glioblastomas from Metastatic Brain Tumors by Tryptophan Uptake and Kinetic Analysis: A Positron Emission Tomographic Study with Magnetic Resonance Imaging Comparison

Differentiating high-grade gliomas from solitary brain metastases is often difficult by conventional magnetic resonance imaging (MRI); molecular imaging may facilitate such discrimination. We tested the accuracy of α[11C]methyl-L-tryptophan (AMT)–positron emission tomography (PET) to differentiate newly diagnosed glioblastomas from brain metastases. AMT-PET was performed in 36 adults with suspected brain malignancy. Tumoral AMT accumulation was measured by standardized uptake values (SUVs). Tracer kinetic analysis was also performed to separate tumoral net tryptophan transport (by AMT volume of distribution [VD]) from unidirectional uptake rates using dynamic PET and blood input function. Differentiating the accuracy of these PET variables was evaluated and compared to conventional MRI. For glioblastoma/metastasis differentiation, tumoral AMT SUV showed the highest accuracy (74%) and the tumor/cortex VD ratio had the highest positive predictive value (82%). The combined accuracy of MRI (size of contrast-enhancing lesion) and AMT-PET reached up to 93%. For ring-enhancing lesions, tumor/cortex SUV ratios were higher in glioblastomas than in metastatic tumors and could differentiate these two tumor types with > 90% accuracy. These results demonstrate that evaluation of tryptophan accumulation by PET can enhance pretreatment differentiation of glioblastomas and metastatic brain tumors. This approach may be particularly useful in patients with a newly diagnosed solitary ring-enhancing mass.

Imaging Copper Metabolism Imbalance in Atp7b−/− Knockout Mouse Model of Wilson’s Disease with PET-CT and Orally Administered 64CuCl2

ObjectivesThis study aims to determine the feasibility and utility of functional imaging of copper metabolism imbalance in Atp7b−/− knockout mouse model of Wilson’s disease (WD) with positron emission tomography-computed tomography (PET-CT) using orally administered copper-64 chloride (64CuCl2) as a tracer.ProceduresAtp7b−/− KO mice (Nu2009=u20095) were subjected to PET scanning using a hybrid PET-CT scanner, after oral administration of 64CuCl2 as a tracer. Time-dependent PET quantitative analysis was performed to assess gastrointestinal absorption and biodistribution of 64Cu radioactivity in the Atp7b−/− KO mice, using C57BL wild-type (WT) mice (Nu2009=u20095) as a normal control. Estimates of human radiation dosimetry were calculated based on biodistribution of 64Cu radioactivity in live animals.ResultsPET-CT analysis demonstrated higher 64Cu radioactivity in the liver of Atp7b−/− knockout mice compared with that in the control C57BL WT mice (pu2009<u20090.001), following oral administration of 64CuCl2 as a tracer. In addition, 64Cu radioactivity in the lungs of the Atp7b−/− knockout mice was slightly higher than those in the control C57BL WT mice (pu2009=u20090.01). Despite initially higher renal clearance of 64Cu, there was no significant difference of 64Cu radioactivity in the kidneys of the Atp7b−/− KO mice and the control C57BL WT mice at 24xa0h post-oral administration of 64CuCl2 (pu2009=u20090.16). There was no significant difference in low 64Cu radioactivity in the blood, brain, heart, and muscles between the Atp7b−/− knockout mice and control C57BL WT mice (pu2009>u20090.05). Based on the biodistribution of 64Cu radioactivity in C57BL WT mice, radiation dosimetry estimates of 64Cu in normal human subjects were obtained. An effective dose (ED) of 42.4xa0μSv/MBq (weighted dose over 22 organs) was calculated and the lower large intestines were identified as the critical organ for radiation exposure (120xa0μGy/MBq for males and 135xa0μGy/MBq for females). Radiation dosimetry estimates for patients with WD, derived from the biodistribution of 64Cu in Atp7b−/− KO mice, showed a slightly lower ED of 37.5xa0μSv/MBq, with the lower large intestines as the critical organ for radiation exposure (83xa0μSv/MBq for male and 95xa0μSv/MBq for female).ConclusionsPET-CT quantitative analysis demonstrated an increased level of 64Cu radioactivity in the liver of Atp7b−/− KO mice compared with that in the control C57BL WT mice, following oral administration of 64CuCl2 as a tracer. The results of this study suggest the feasibility and utility of PET-CT using orally administered 64CuCl2 as a tracer (64CuCl2-PET/CT) for functional imaging of copper metabolism imbalance in WD.