Matthias Bauwens

BMP7 activates brown adipose tissue and reduces diet-induced obesity only at subthermoneutrality

Background/Aims Brown adipose tissue (BAT) dissipates energy stored in triglycerides as heat via the uncoupling protein UCP-1 and is a promising target to combat hyperlipidemia and obesity. BAT is densely innervated by the sympathetic nervous system, which increases BAT differentiation and activity upon cold exposure. Recently, Bone Morphogenetic Protein 7 (BMP7) was identified as an inducer of BAT differentiation. We aimed to elucidate the role of sympathetic activation in the effect of BMP7 on BAT by treating mice with BMP7 at varying ambient temperature, and assessed the therapeutic potential of BMP7 in combating obesity. Methods and Results High-fat diet fed lean C57Bl6/J mice were treated with BMP7 via subcutaneous osmotic minipumps for 4 weeks at 21°C or 28°C, the latter being a thermoneutral temperature in which sympathetic activation of BAT is largely diminished. At 21°C, BMP7 increased BAT weight, increased the expression of Ucp1, Cd36 and hormone-sensitive lipase in BAT, and increased total energy expenditure. BMP7 treatment markedly increased food intake without affecting physical activity. Despite that, BMP7 diminished white adipose tissue (WAT) mass, accompanied by increased expression of genes related to intracellular lipolysis in WAT. All these effects were blunted at 28°C. Additionally, BMP7 resulted in extensive ‘browning’ of WAT, as evidenced by increased expression of BAT markers and the appearance of whole clusters of brown adipocytes via immunohistochemistry, independent of environmental temperature. Treatment of diet-induced obese C57Bl6/J mice with BMP7 led to an improved metabolic phenotype, consisting of a decreased fat mass and liver lipids as well as attenuated dyslipidemia and hyperglycemia. Conclusion Together, these data show that BMP7-mediated recruitment and activation of BAT only occurs at subthermoneutral temperature, and is thus likely dependent on sympathetic activation of BAT, and that BMP7 may be a promising tool to combat obesity and associated disorders.

Molecular imaging of brown adipose tissue in health and disease

PurposeBrown adipose tissue (BAT) has transformed from an interfering tissue in oncological 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) to an independent imaging research field. This review takes the perspective from the imaging methodology on which human BAT research has come to rely on heavily.MethodsThis review analyses relevant PubMed-indexed publications that discuss molecular imaging methods of BAT. In addition, reported links between BAT and human diseases such as obesity are discussed, and the possibilities for imaging in these fields are highlighted. Radiopharmaceuticals aiming at several different biological mechanisms of BAT are discussed and evaluated.ResultsProspective, dedicated studies allow visualization of BAT function in a high percentage of human subjects. BAT dysfunction has been implicated in obesity, linked with diabetes and associated with cachexia and atherosclerosis. Presently, 18F-FDG PET/CT is the most useful tool for evaluating therapies aiming at BAT activity. In addition to 18F-FDG, other radiopharmaceuticals such as 99mTc-sestamibi, 123I-metaiodobenzylguanidine (MIBG), 18F-fluorodopa and 18F-14(R,S)-[18F]fluoro-6-thia-heptadecanoic acid (FTHA) may have a potential for visualizing other aspects of BAT activity. MRI methods are under continuous development and provide the prospect of functional imaging without ionizing radiation.ConclusionMolecular imaging of BAT can be used to quantitatively assess different aspects of BAT metabolic activity.

Optimal buffer choice of the radiosynthesis of 68ga–dotatoc for clinical application

Objectives68Ga–Dotatoc has become the PET radiopharmaceutical of choice for the diagnosis and treatment follow-up of neuroendocrine tumours. 68Ga–Dotatoc is prepared on-site through a so-called magisterial preparation. The use of an appropriate buffer during the radiolabelling step is essential to maximize the labelling yield and the specific activity. Such a buffer should be nontoxic, able to buffer in the pH range of 3.5–5.0, not compete with gallium ions and preferentially have a weak metal complexing capacity to avoid the formation of colloidal gallium. In addition, the buffer should be allowed for human use. In view of the high radiation dose to the operator when manually handling 68Ga, especially to the extremities, we also tested the buffers in a semi-automated system. MethodsHEPES, acetate, succinate, Tris, glutamate, lactate, oxalate and tartrate were tested as potential buffers in the manual radiosynthesis of 68Ga–Dotatoc. Temperature, heating time and substrate concentration were optimized. ResultsBuffers based on HEPES, acetate and succinate were found to be the most appropriate. Optimal labelling yields were achieved with a 5-min heating time for the manual synthesis and 8 min for a semi-automated system, whereas the optimal amount of Dotatoc was 30 and 40 μg, respectively. ConclusionAlthough the use of HEPES, acetate and succinate as buffering substances yielded comparable results, only acetate is currently recognized as a substance for pharmaceutical use and also for human use. Therefore, acetate buffer should be used for 68Ga–Dotatoc synthesis. The semi-automated system allowed for a shorter radiosynthesis time, thereby increasing the overall yield.

Pharmacological Treatment with Annexin A1 Reduces Atherosclerotic Plaque Burden in LDLR-/- Mice on Western Type Diet.

Objective To investigate therapeutic effects of annexin A1 (anxA1) on atherogenesis in LDLR-/- mice. Methods Human recombinant annexin A1 (hr-anxA1) was produced by a prokaryotic expression system, purified and analysed on phosphatidylserine (PS) binding and formyl peptide receptor (FPR) activation. Biodistribution of 99mTechnetium-hr-anxA1 was determined in C57Bl/6J mice. 12 Weeks old LDLR-/- mice were fed a Western Type Diet (WTD) during 6 weeks (Group I) or 12 weeks (Group P). Mice received hr-anxA1 (1 mg/kg) or vehicle by intraperitoneal injection 3 times per week for a period of 6 weeks starting at start of WTD (Group I) or 6 weeks after start of WTD (Group P). Total aortic plaque burden and phenotype were analyzed using immunohistochemistry. Results Hr-anxA1 bound PS in Ca2+-dependent manner and activated FPR2/ALX. It inhibited rolling and adherence of neutrophils but not monocytes on activated endothelial cells. Half lives of circulating 99mTc-hr-anxA1 were <10 minutes and approximately 6 hours for intravenously (IV) and intraperitoneally (IP) administered hr-anxA1, respectively. Pharmacological treatment with hr-anxA1 had no significant effect on initiation of plaque formation (-33%; P = 0.21)(Group I) but significantly attenuated progression of existing plaques of aortic arch and subclavian artery (plaque size -50%, P = 0.005; necrotic core size -76% P = 0.015, hr-anxA1 vs vehicle) (Group P). Conclusion Hr-anxA1 may offer pharmacological means to treat chronic atherogenesis by reducing FPR-2 dependent neutrophil rolling and adhesion to activated endothelial cells and by reducing total plaque inflammation.

I-123/125-labelled 2-iodo-L-phenylalanine and 2-iodo-D-phenylalanine : comparative uptake in various tumour types and biodistribution in mice

PurposeIn vitro in the R1M cell model and in vivo in the R1M tumour-bearing athymic model, both [123I]-2-iodo-L-phenylalanine and [123I]-2-iodo-D-phenylalanine have shown promising results as tumour diagnostic agents for SPECT. In order to compare these two amino acid analogues and to examine whether the observed characteristics could be generalised, both isomers were evaluated in various tumour models.MethodsTransport type characterisation in vitro in A549, A2058, C6, C32, Capan2, EF43fgf4, HT29 and R1M cells with [123I]-2-iodo-L-phenylalanine was performed using the method described by Shotwell et al. Subsequently, [123I]-2-iodo-L-phenylalanine and [123I]-2-iodo-D-phenylalanine tumour uptake and biodistribution were evaluated using dynamic planar imaging and/or dissection in A549, A2058, C6, C32, Capan2, EF43fgf4, HT29 and R1M inoculated athymic mice. Two-compartment blood modelling of the imaging results was performed.ResultsIn vitro testing demonstrated that [123I]-2-iodo-L-phenylalanine was transported in all tumour cell lines by LAT1. In all tumour models, the two amino acid analogues showed the same general biodistribution characteristics: high and specific tumour uptake and renal tracer clearance. Two-compartment modelling revealed that the D-isomer showed a faster blood clearance together with a faster distribution to the peripheral compartment in comparison with [123I]-2-iodo-L-phenylalanine.Conclusion[123I]-2-iodo-L-phenylalanine and its D-isomer are promising tumour diagnostic agents for dynamic planar imaging. They showed a high and similar uptake in all tested tumours. [123I]-2-iodo-D-phenylalanine showed better tracer characteristics concerning radiation dose to other organs.

99m) Tc radiolabeling and biological evaluation of nanoparticles functionalized with a versatile coating ligand

Radiolabeling allows noninvasive imaging by single photon emission computed tomography (SPECT) or positron emission tomography (PET) for assessing the biodistribution of nanostructures. Herein, the synthesis of a new coating ligand for gold nanoparticles (AuNPs) and quantum dots (QDs) is reported. This ligand is multifunctional; it combines the metal chelate with conjugating functions to biological vectors. The concept allows the coupling of any targeting function to the chelator; an example for the prostate specific membrane antigen is given. Derivatized NPs can directly be labeled in one step with [(99m) Tc(OH2 )3 (CO)3 ](+) . AuNPs in particular are highly stable, a prerequisite for in vivo studies excluding misinterpretation of the biodistribution data. AuNPs with differing sizes (7 and 14 nm core diameter) were administered intravenously into nude NMRI mice bearing LNCaP xenografts. MicroSPECT images show for both probes rapid clearance from the blood pool through the hepatobiliary pathway. The 7 nm AuNPs revealed a significantly higher bone uptake than the 14 nm AuNPs. The high affinity towards bone mineral is further confirmed in vitro with hydroxyapatite.

Nuclear Targeting with an Auger Electron Emitter Potentiates the Action of a Widely Used Antineoplastic Drug

We present the combination of the clinically well-proven chemotherapeutic agent, Doxorubicin, and (99m)Tc, an Auger and internal conversion electron emitter, into a dual-action agent for therapy. Chemical conjugation of Doxorubicin to (99m)Tc afforded a construct which autonomously ferries a radioactive payload into the cell nucleus. At this site, damage is exerted by dose deposition from Auger radiation. The (99m)Tc-conjugate exhibited a dose-dependent inhibition of survival in a selected panel of cancer cells and an in vivo study in healthy mice evidenced a biodistribution which is comparable to that of the parent drug. The homologous Rhenium conjugate was found to effectively bind to DNA, inhibited human Topoisomerase II, and exhibited cytotoxicity in vitro. The collective in vitro and in vivo data demonstrate that the presented metallo-conjugates closely mimic native Doxorubicin.

Synthesis and in Vivo Biological Evaluation of 68Ga-Labeled Carbonic Anhydrase IX Targeting Small Molecules for Positron Emission Tomography

Tumor hypoxia contributes resistance to chemo- and radiotherapy, while oxygenated tumors are sensitive to these treatments. The indirect detection of hypoxic tumors is possible by targeting carbonic anhydrase IX (CA IX), an enzyme overexpressed in hypoxic tumors, with sulfonamide-based imaging agents. In this study, we present the design and synthesis of novel gallium-radiolabeled small-molecule sulfonamides targeting CA IX. The compounds display favorable in vivo pharmacokinetics and stability. We demonstrate that our lead compound, [(68)Ga]-2, discriminates CA IX-expressing tumors in vivo in a mouse xenograft model using positron emission tomography (PET). This compound shows specific tumor accumulation and low uptake in blood and clears intact to the urine. These findings were reproduced in a second study using PET/computed tomography. Small molecules investigated to date utilizing (68)Ga for preclinical CA IX imaging are scarce, and this is one of the first effective (68)Ga compounds reported for PET imaging of CA IX.

Impact of bariatric surgery on carotid artery inflammation and the metabolic activity in different adipose tissues

AbstractIn this study, we unravel a molecular imaging marker correlated with the known reduction of cardiovascular events (most commonly related to vulnerable plaques) in morbidly obese patients after bariatric surgery (BaS).We prospectively imaged 10 morbidly obese subjects with 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography before and 1 year after BaS. 18F-FDG uptake—which is enhanced in inflamed, atherosclerotic vessels and in metabolically active adipose tissues—was quantified in the carotids, pericardial adipose tissue (PAT), visceral adipose tissue (VAT), as well as brown adipose tissue (BAT). The degree of carotid inflammation was compared to lean and overweight controls.Carotid inflammation significantly declined leading to an 18F-FDG uptake comparable to the 2 control groups. Metabolic activity significantly decreased in PAT and VAT and increased in BAT.BaS leads to a normalization of carotid artery inflammation and a beneficial impact on the metabolic activity in PAT, VAT, and BAT that is related to the metabolic syndrome observed in this patient group.

Method for stabilizing non carrier added 2-[18F]fluoromethyl-l-phenylalanine, a new tumour tracer, during radiosynthesis and radiopharmaceutical formulation

INTRODUCTION Non carrier added (NCA) 2-[(18)F]fluoromethyl-l-phenylalanine is currently used in a Phase I study. Improvement of the stability of the fluorobenzyl analogue, very sensitive to defluorination and hydrolysis, during the synthetic route and in the radiopharmaceutical formulation was devised. METHODS The protected brominated precursor was synthesised in three steps. The labelling with [(18)F(-)] occurred in acetonitrile using K(2)CO(3)/K(2.2.2) (120 degrees C, 5 min). NCA 3-(2-[(18)F(-)]Fluoromethyl-phenyl)-2-tert-butoxycarbonylamino-propionic acid tert-butyl ester recovered from HPLC was submitted to deprotection in TFA/CH(2)Cl(2) in the presence of CaCl(2). After evaporation and adsorption on a mini C18 column, the tracer was recovered in 4 ml of H(2)O. Appropriate amounts of CaCl(2) and NaCl solutions were added for isotonic formulation, and this solution was sterilised by a 0.2-microm Cathivex filter. Shelf-life stability in the presence of Ca(2+) and Mg(2+) ions was studied. Stereoisomeric purity was checked by chiral HPLC. RESULTS The labelling showed a reproducible labelling yield of at least 90%. The followed strategy and the presence of Ca(2+) ions during deprotection, minimizing the loss of [(18)F(-)] from the labile fluorobenzyl group, allowed to obtain a decay-corrected yield of 75%. No racemisation was observed. The radiopharmaceutical formulation containing 0.04 M CaCl(2) allows a shelf-life of about 6 h without significant radiodefluorination. CONCLUSION The described synthetic route yields 40% of radiochemical pure NCA 2-[(18)F]fluoromethyl-l-phenylalanine within 105 min. A solution was found to reduce considerably the radiodefluorination. Addition of CaCl(2) prior to deprotection limits the loss of radiofluoride to less than 10%. The calcium ions present in the final radiopharmaceutical formulation (0.04 M) assure a shelf-life of at least 6 h.