M. Reza Mirbolooki

Quantitative assessment of brown adipose tissue metabolic activity and volume using 18F-FDG PET/CT and β3-adrenergic receptor activation

BackgroundBrown adipose tissue [BAT] metabolism in vivo is vital for the development of novel strategies in combating obesity and diabetes. Currently, BAT is activated at low temperatures and measured using 2-deoxy-2-18F-fluoro-D-glucose [18F-FDG] positron-emission tomography [PET]. We report the use of β3-adrenergic receptor-mediated activation of BAT at ambient temperatures using (R, R)-5-[2-[2,3-(3-chlorphenyl)-2-hydroxyethyl-amino]propyl]-1,3-benzodioxole-2,2-dicarboxylate, disodium salt [CL316,243] (a selective β3-adrenoceptor agonist) and measured by 18F-FDG PET/computed tomography [CT].MethodsControl and CL316,243-treated (2 mg/kg) male Sprague-Dawley rats were administered with 18F-FDG for PET/CT studies and were compared to animals at cold temperatures. Receptor-blocking experiments were carried out using propranolol (5 mg/kg). Dose effects of CL316,243 were studied by injecting 0.1 to 1 mg/kg 30 min prior to 18F-FDG administration. Imaging results were confirmed by autoradiography, and histology was done to confirm BAT activation.ResultsCL316,243-activated interscapular BAT [IBAT], cervical, periaortic, and intercostal BATs were clearly visualized by PET. 18F-FDG uptake of IBAT was increased 12-fold by CL316,243 vs. 1.1-fold by cold exposure when compared to controls. 18F-FDG uptake of the CL-activated IBAT was reduced by 96.0% using intraperitoneal administration of propranolol. Average 18F-FDG uptake of IBAT increased 3.6-, 3.5-, and 7.6-fold by doses of 0.1, 0.5, and 1 mg/kg CL, respectively. Ex vivo18F-FDG autoradiography and histology of transverse sections of IBAT confirmed intense uptake in the CL-activated group and activated IBAT visualized by PET.ConclusionOur study indicated that BAT metabolic activity could be evaluated by 18F-FDG PET using CL316,243 at ambient temperature in the rodent model. This provides a feasible and reliable method to study BAT metabolism.

Adrenergic pathway activation enhances brown adipose tissue metabolism: A [18 F]FDG PET/CT study in mice

OBJECTIVE Pharmacologic approaches to study brown adipocyte activation in vivo with a potential of being translational to humans are desired. The aim of this study was to examine pre- and postsynaptic targeting of adrenergic system for enhancing brown adipose tissue (BAT) metabolism quantifiable by [(18)F]fluoro-2-deoxyglucose ([(18)F]FDG) positron emission tomography (PET)/computed tomography (CT) in mice. METHODS A β₃-adrenoreceptor selective agonist (CL 316243), an adenylyl cyclase enzyme activator (forskolin) and a potent blocker of presynaptic norepinephrine transporter (atomoxetine), were injected through the tail vein of Swiss Webster mice 30 minutes before intravenous (iv) administration of [(18)F]FDG. The mice were placed on the PET/CT bed for 30 min PET acquisition followed by 10 min CT acquisition for attenuation correction and anatomical delineation of PET images. RESULTS Activated interscapular (IBAT), cervical, periaortic and intercostal BAT were observed in 3-dimentional analysis of [(18)F]FDG PET images. CL 316243 increased the total [(18)F]FDG standard uptake value (SUV) of IBAT 5-fold greater compared to that in placebo-treated mice. It also increased the [(18)F]FDG SUV of white adipose tissue (2.4-fold), and muscle (2.7-fold), as compared to the control. There was no significant difference in heart, brain, spleen and liver uptakes between groups. Forskolin increased [(18)F]FDG SUV of IBAT 1.9-fold greater than that in placebo-treated mice. It also increased the [(18)F]FDG SUV of white adipose tissue (2.2-fold) and heart (5.4-fold) compared to control. There was no significant difference in muscle, brain, spleen, and liver uptakes between groups. Atomoxetine increased [(18)F]FDG SUV of IBAT 1.7-fold greater than that in placebo-treated mice. There were no significant differences in all other organs compared to placebo-treated mice except liver (1.6 fold increase). A positive correlation between SUV levels of IBAT and CT Hounsfield unit (HU) (R(2)=0.55, p<0.001) and between CT HU levels of IBAT and liver (R(2)=0.69, p<0.006) was observed. CONCLUSIONS The three pharmacologic approaches reported here enhanced BAT metabolism by targeting different sites in adrenergic system as measured by [(18)F]FDG PET/CT.

Targeting presynaptic norepinephrine transporter in brown adipose tissue: a novel imaging approach and potential treatment for diabetes and obesity.

Brown adipose tissue (BAT) plays a significant role in metabolism. In this study, we report the use of atomoxetine (a clinically applicable norepinephrine reuptake inhibitor) for 18F‐FDG PET imaging of BAT and its effects on heat production and blood glucose concentration. Fasted‐male Sprague‐Dawley rats were administered with intravenous 18F‐FDG. The same rats were treated with atomoxetine (0.1 mg/kg, i.v.) 30 min before 18F‐FDG administration. To confirm the β‐adrenergic effects, propranolol (β‐adrenergic inhibitor) 5 mg/kg was given intraperitoneally 30 min prior to atomoxetine administration. The effect of atomoxetine on BAT metabolism was assessed in fasted and non‐fasted rats and on BAT temperature and blood glucose in fasted rats. In 18F‐FDG PET/CT images, interscapular BAT (IBAT) and other areas of BAT were clearly visualized. When rats were fasted, atomoxetine (0.1 mg/kg) increased the 18F‐FDG uptake of IBAT by factor of 24 within 30 min. Propranolol reduced the average 18F‐FDG uptake of IBAT significantly. Autoradiography of IBAT and white adipose tissue confirmed the data obtained by PET. When rats were not fasted, atomoxetine‐induced increase of 18F‐FDG uptake in IBAT was delayed and occurred in 120 min. For comparison, direct stimulation of β3‐adrenreceptors in non‐fasted rats with CL‐316, 243 occurred within 30 min. Atomoxetine‐induced IBAT activation was associated with higher IBAT temperature and lower blood glucose. This was mediated by inhibition of norepinephrine reuptake transporters in IBAT leading to increased norepinephrine concentration in the synapse. Increased synaptic norepinephrine activates β3‐adrenreceptors resulting in BAT hypermetabolism that is visible and quantifiable by 18F‐FDG PET/CT. Synapse, 2013.

Evaluation of [18F]Nifene biodistribution and dosimetry based on whole-body PET imaging of mice.

INTRODUCTION [(18)F]Nifene is a novel radiotracer specific to the nicotinic acetylcholine α4β2 receptor class. In preparation for using this tracer in humans we have performed whole-body PET studies in mice to evaluate the in vivo biodistribution and dosimetry of [(18)F]Nifene. METHODS Seven BALB/c mice (3 males, 4 females) received IV tail injections of [(18)F]Nifene and were scanned for 2 h in an Inveon dedicated PET scanner. Each animal also received a high resolution CT scan using an Inveon CT. The CT images were used to draw volume of interest (VOI) on the following organs: brain, large intestine, small intestine, stomach, heart, kidneys, liver, lungs, pancreas, bone, spleen, testes, thymus, uterus and urinary bladder. All organ time activity curves had the decay correction reversed and were normalized to the injected activity. The area under the normalized curves was then used to compute the residence times in each organ. The absorbed doses in mouse organs were computed using the RAdiation Dose Assessment Resource (RADAR) animal models for dose assessment. The residence times in mouse organs were converted to human values using scale factors based on differences between organ and body weights. OLINDA 1.1 software was used to compute the absorbed human doses in multiple organs for both female and male phantoms. RESULTS The highest mouse residence times were found in urinary bladder, liver, bone, small intestine and kidneys. The largest doses in mice were found in urinary bladder and kidneys for both females and males. The elimination of radiotracer was primarily via kidney and urinary bladder with the urinary bladder being the limiting organ. The projected human effective doses were 1.51E-02 mSv/MBq for the adult male phantom and 1.65E-02 mSv/MBq for the adult female model phantom. CONCLUSION This study indicates that the whole-body mouse imaging can be used as a preclinical tool for initial estimation of the absorbed doses of [(18)F]Nifene in humans.

Extracellular CADM1 interactions influence insulin secretion by rat and human islet β-cells and promote clustering of syntaxin-1

Contact between β-cells is necessary for their normal function. Identification of the proteins mediating the effects of β-cell-to-β-cell contact is a necessary step toward gaining a full understanding of the determinants of β-cell function and insulin secretion. The secretory machinery of the β-cells is nearly identical to that of central nervous system (CNS) synapses, and we hypothesize that the transcellular protein interactions that drive maturation of the two secretory machineries upon contact of one cell (or neural process) with another are also highly similar. Two such transcellular interactions, important for both synaptic and β-cell function, have been identified: EphA/ephrin-A and neuroligin/neurexin. Here, we tested the role of another synaptic cleft protein, CADM1, in insulinoma cells and in rat and human islet β-cells. We found that CADM1 is a predominant CADM isoform in β-cells. In INS-1 cells and primary β-cells, CADM1 constrains insulin secretion, and its expression decreases after prolonged glucose stimulation. Using a coculture model, we found that CADM1 also influences insulin secretion in a transcellular manner. We asked whether extracellular CADM1 interactions exert their influence via the same mechanisms by which they influence neurotransmitter exocytosis. Our results suggest that, as in the CNS, CADM1 interactions drive exocytic site assembly and promote actin network formation. These results support the broader hypothesis that the effects of cell-cell contact on β-cell maturation and function are mediated by the same extracellular protein interactions that drive the formation of the presynaptic exocytic machinery. These interactions may be therapeutic targets for reversing β-cell dysfunction in diabetes.

Enhancement of 18F-fluorodeoxyglucose metabolism in rat brain frontal cortex using a β3 adrenoceptor agonist.

We report the use of β3 adrenergic receptor mediated activation of rat brain frontal cortex using mirabegron (a selective β3 adrenoceptor agonist), measured by 18F‐FDG PET/CT. Another β3 agonist, CL 316,243, did not have this effect due to impermeability through the blood brain barrier (BBB), while atomoxetine, a norepinephrine transporter blocker, did increase 18F‐FDG uptake in the frontal cortex. Mirabegron exhibited a dose‐dependent increase in frontal cortex 18F‐FDG uptake. These findings suggest a possible use of selective β3 adrenoceptor agonists in reversing regional glucose hypometabolism in the brain. Synapse 69:96–98, 2015.

Pulsatile intravenous insulin therapy: The best practice to reverse diabetes complications?

In the basal state and after oral ingestion of carbohydrate, the normal pancreas secretes insulin into the portal vein in a pulsatile manner. The end organ of the portal vein is the liver, where approximately 80% of pancreatic insulin is extracted during first pass. In Type 1 diabetes, pancreatic insulin secretion is nearly or completely absent whilst in Type 2 diabetes the normal pattern is absent, abnormal, or blunted. Exogenous subcutaneous insulin treatment results in plasma insulin concentrations that are not pulsatile and a fraction of normal portal vein levels. Oral hypoglycemic agents also do not result in normal pulsatile response to a glucose load. Due to hypoglycemia risk, intensive treatment is not recommended after serious complications develop. Consequently, no conventional therapy has proved effective in treating advanced diabetes complications. Beta-cell replacement using whole pancreas or islet transplantation has been utilized to treat certain problems in Type 1 diabetic patients, but still unavailable for all diabetics. Pulsatile intravenous insulin therapy (PIVIT) is an insulin therapy, which mimics the periodicity and amplitude of normal pancreatic function. Numerous studies show PIVIT effective in preventing, reversing, and reducing the severity and progression of diabetes complications, however, the mechanisms involved with the improvement are not clearly understood. Here, we review the cellular basis of normal and abnormal insulin secretion, current treatments available to treat diabetes, the physiologic basis of PIVIT and possible mechanisms of action.

Preliminary evaluation of β3-adrenoceptor agonist-induced 18F-FDG metabolic activity of brown adipose tissue in obese Zucker rat.

BACKGROUND We have investigated β3-adrenoceptor agonist mediated brown adipose tissue (BAT) activation using (18)F-FDG PET/CT in Zucker lean (ZL) and obese (ZF) rats. METHODS (18)F-FDG was injected into ZL and ZF rats pretreated with saline or agonist CL316,243 for scans. (18)F-FDG metabolic activity was computed as standard uptake values. RESULTS CL316,243 in ZL activated BAT up to 4-fold compared to saline, while ZF BAT was only up by 2 fold. The decreased activation was consistent with lower β3-adrenoceptor levels in ZF rats. CONCLUSIONS The genetically modified ZL and ZF rats may provide a useful rat model to evaluate the significance of β3-adrenoceptor agonist-induced BAT activation in obesity.

Evaluation of [11C]TAZA for amyloid β plaque imaging in postmortem human Alzheimer's disease brain region and whole body distribution in rodent PET/CT.

Objective: Alzheimers disease (AD) is a neurodegenerative disease characterized by Aβ plaques in the brain. The aim of this study was to evaluate the effectiveness of a novel radiotracer, 4‐[11C]methylamino‐4′‐N,N‐dimethylaminoazobenzene ([11C]TAZA), for binding to Aβ plaques in postmortem human brain (AD and normal control (NC)). Methods: Radiosyntheses of [11C]TAZA, related [11C]Dalene (11C‐methylamino‐4′‐dimethylaminostyrylbenzene), and reference [11C]PIB were carried out using [11C]methyltriflate prepared from [11C]CO2 and purified using HPLC. In vitro binding affinities were carried out in human AD brain homogenate with Aβ plaques labeled with [3H]PIB. In vitro autoradiography studies with the three radiotracers were performed on hippocampus of AD and NC brains. PET/CT studies were carried out in normal rats to study brain and whole body distribution. Results: The three radiotracers were produced in high radiochemical yields (>40%) and had specific activities >37 GBq/μmol. TAZA had an affinity, Ki = 0.84 nM and was five times more potent than PIB. [11C]TAZA bound specifically to Aβ plaques present in AD brains with gray matter to white matter ratios >20. [11C]TAZA was displaced by PIB (>90%), suggesting similar binding site for [11C]TAZA and [11C]PIB. [11C]TAZA exhibited slow kinetics of uptake in the rat brain and whole body images showed uptake in interscapular brown adipose tissue (IBAT). Binding in brain and IBAT were affected by preinjection of atomoxetine, a norepinephrine transporter blocker. Conclusion: [11C]TAZA exhibited high binding to Aβ plaques in human AD hippocampus. Rat brain kinetics was slow and peripheral binding to IBAT needs to be further evaluated. Synapse, 2016.

Initial Assessment of β3-Adrenoceptor-Activated Brown Adipose Tissue in Streptozotocin-Induced Type 1 Diabetes Rodent Model Using [18F]Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography

Metabolic activity of brown adipose tissue (BAT) is activated by β3-adrenoceptor agonists and norepinephrine transporter (NET) blockers and is measurable using [18F]fluorodeoxyglucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) in rats. Using the streptozotocin (STZ)-treated rat model of type 1 diabetes mellitus (T1DM), we investigated BAT activity in this rat model under fasting and nonfasting conditions using [18F]FDG PET/CT. Drugs that enhance BAT activity may have a potential for therapeutic development in lowering blood sugar in insulin-resistant diabetes. Rats were rendered diabetic by administration of STZand confirmed by glucose measures. [18F]FDG was injected in the rats (fasted or nonfasted) pretreated with either saline or β3-adrenoceptor agonist CL316,243 or the NET blocker atomoxetine for PET/CT scans. [18F]FDG metabolic activity was computed as standard uptake values (SUVs) in interscapular brown adipose tissue (IBAT) and compared across the different drug treatment conditions. Blood glucose levels > 500 mg/dL were established for the STZ-treated diabetic rats. Under fasting conditions, average uptake of [18F]FDG in the IBAT of STZ-treated diabetic rats was approximately 70% lower compared to that of normal rats. Both CL316,243 and atomoxetine activated IBAT in normal rats had an SUV > 5, whereas activation in STZ-treated rats was significantly lower. The agonist CL316,243 activated IBAT up to threefold compared to saline in the fasted STZ-treated rat. In the nonfasted rat, the IBAT activation was up by twofold by CL316243. Atomoxetine had a greater effect on lowering blood sugar levels compared to CL316,243 in the nonfasted rats. A significant reduction in metabolic activity was observed in the STZ-treated diabetic rodent model. Increased IBAT activity in the STZ-treated diabetic rat under nonfasted conditions using the β3-adrenoceptor agonist CL316,243 suggests a potential role of BAT in modulating blood sugar levels. Further studies are needed to evaluate the therapeutic role of β3-adrenoceptor agonists in insulin-resistant T1DM.