18F-labelled CCR1-receptor antagonist is not suitable for imaging of Alzheimer's disease.

Diagnosis of Alzheimer's disease (AD) with positron emission tomography (PET) using 18F-fluorodeoxyglucose (FDG) relies on typical alterations of brain glucose metabolism which are, however, not disease specific. Amyloid-ß imaging has not entered clinical routine yet. Post mortem histological specimen of brain tissue from AD patients revealed enhanced expression of the chemotactic cytocine receptor 1 (CCR1). PARTICIPANTS, METHODS: CCR1-antagonist ZK811460 was labeled with fluorine-18 to explore its possible use as specific diagnostic tool in AD. Tracer characterization comprising PET imaging of brain and metabolite analysis was performed in AD patients and controls. RESULTS: Neither qualitative evaluation nor quantitative compartment analysis of PET data did show any enhanced binding of the 18F-labeled CCR1-antagonist in the brain of AD patients or controls. CONCLUSION: 18F-ZK811460 did not fulfill the expectation as diagnostic tracer in PET imaging of AD.

Synthesis and biodistribution of an 18F-labelled resveratrol derivative for small animal positron emission tomography.

Resveratrol (3,4',5-trihydroxy-trans-stilbene) is a naturally occurring phytoalexin and polyphenol existing in grapes and various other plants, and one of the best known 'nutriceuticals'. It shows a multiplicity of beneficial biological effects, particularly, by attenuating atherogenic, inflammatory, and carcinogenic processes. However, despite convincing evidence from experimental and clinical studies, data concerning the role of resveratrol and other members of the large polyphenols family for human health is still a matter of debate. One reason for this is the lack of suitable sensitive and specific methods, which would allow direct assessment of biodistribution, biokinetics, and the metabolic fate of these compounds in vivo. The unique features of positron emission tomography (PET) as a non-invasive in vivo imaging methodology in combination with suitable PET radiotracers have great promise to assess quantitative information on physiological effects of polyphenols in vivo. Herein we describe the radiosynthesis of an (18)F-labelled resveratrol derivative, 3,5-dihydroxy-4'-[(18)F]fluoro-trans-stilbene ([(18)F]-1), using the Horner-Wadsworth-Emmons reaction as a novel radiolabelling technique in PET radiochemistry for subsequent functional imaging of polyphenol metabolism in vivo. In a typical "three-step/one-pot" reaction, (18)F-labelled resveratrol derivative [(18)F]-1 could be synthesized within 120-130 min including HPLC separation at a specific radioactivity of about 90 GBq/mumol. The radiochemical yield was about 9% (decay-corrected) related to [(18)F]fluoride and the radiochemical purity exceeded 97%. First radiopharmacological evaluation included measurement of biodistribution ex vivo and positron emission tomography (PET) studies in vivo after intravenous application of [(18)F]-1 in male Wistar rats using a dedicated small animal PET camera with very high spatial resolution. Concordantly with data on bioavailability and metabolism of native resveratrol from the literature, these investigations revealed an extensive uptake and metabolism in the liver and kidney, respectively, of [(18)F]-1. This study represents the first investigation of polyphenols in vivo by means of PET.

Catabolism of native and oxidized low density lipoproteins: in vivo insights from small animal positron emission tomography studies.

The human organism is exposed to numerous processes that generate reactive oxygen species (ROS). ROS may directly or indirectly cause oxidative modification and damage of proteins. Protein oxidation is regarded as a crucial event in the pathogenesis of various diseases ranging from rheumatoid arthritis to Alzheimer's disease and atherosclerosis. As a representative example, oxidation of low density lipoprotein (LDL) is regarded as a crucial event in atherogenesis. Data concerning the role of circulating oxidized LDL (oxLDL) in the development and outcome of diseases are scarce. One reason for this is the shortage of methods for direct assessment of the metabolic fate of circulating oxLDL in vivo. We present an improved methodology based on the radiolabelling of apoB-100 of native LDL (nLDL) and oxLDL, respectively, with the positron emitter fluorine-18 ((18)F) by conjugation with N-succinimidyl-4-[(18)F]fluorobenzoate ([(18)F]SFB). Radiolabelling of both nLDL and oxLDL using [(18)F]SFB causes neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality, respectively, in vitro. The method was further evaluated with respect to the radiopharmacological properties of both [(18)F]fluorobenzoylated nLDL and oxLDL by biodistribution studies in male Wistar rats. The metabolic fate of [(18)F]fluorobenzoylated nLDL and oxLDL in rats in vivo was further delineated by dynamic positron emission tomography (PET) using a dedicated small animal tomograph (spatial resolution of 2 mm). From this study we conclude that the use of [(18)F]FB-labelled LDL particles is an attractive alternative to, e.g., LDL iodination methods, and is of value to characterize and to discriminate the kinetics and the metabolic fate of nLDL and oxLDL in small animals in vivo.

Biodistribution and catabolism of 18F-labelled isopeptide N(epsilon)-(gamma-glutamyl)-L-lysine.

Isopeptide bonds between the epsilon-amino group of lysine and the gamma-carboxamide group of glutamine are formed during strong heating of pure proteins or, more important, by enzymatic reaction mediated by transglutaminases. Despite the wide use of a microbial transglutaminase in food biotechnology, up to now little is known about the metabolic fate of the isopeptide N(epsilon)-(gamma-glutamyl)-L-lysine. In the present study, N-succinimidyl-4-[(18)F]fluorobenzoate was used to modify N(epsilon)-(gamma-glutamyl)-L-lysine at each of its two alpha-amino groups, resulting in the 4-[(18)F]fluorobenzoylated derivatives, for which biodistribution, catabolism, and elimination were investigated in male Wistar rats. A significant different biochemical behavior of the two labelled isopeptides was observed in terms of in vitro stability, in vivo metabolism as well as biodistribution. The results suggest that the metabolic fate of isopeptides is likely to be dependent on how they are reabsorbed - free or peptide bound.

Metabolite analysis in positron emission tomography studies: examples from food sciences.

Substances of various chemical structures can be labelled with appropriate positron emitting isotopes and applied as tracer compounds in PET examinations. Using dynamic data acquisition protocols, time-activity curves of radioactivity uptake in organs can be derived and the measurements of tissue tracer concentrations can be translated into quantitative values of tissue function. However, analysis of metabolites of these tracers regarding their nature and distribution in the living organism is an essential need for the quantitative analysis of PET measurements. In addition, metabolite analysis contributes to the interpretation of the images obtained as well as to the identification of pathological changes in metabolic pathways. This paper reports on representative examples of radiolabelled compounds which might be of importance in food science (e.g., amino acids, polyphenols, and model compounds for advanced glycation end products (AGEs)). Typical procedures of analysis (radio-HPLC, radio-TLC) including pre-analytical sample preparation are described. Specific challenges of the method, e.g., trace amounts of radiolabelled compounds and the influence of the often very short half-lives of positron-emitting nuclides used are highlighted. Representative results of analyses of plasma, urine, and tissue samples are presented and discussed in terms of the metabolic fate of the tracers.

Novel procedures for preparing 99mTc(III) complexes with tetradentate/monodentate coordination of varying lipophilicity and adaptation to 188Re analogues.

Improved methods are presented for the preparation of 99mTc and 188Re mixed-ligand complexes with tetradentate and monodentate ligands of the general formula [MIII(Lm)(Ln)] (M = Tc, Re; Lm = NS3 or NS3COOH; Ln = isocyanide or phosphine). To avoid the undesired formation of reduced-hydrolyzed species of both metals, the preparation of complexes is performed in a two-step procedure. At first the Tc(III)- or Re(III)-EDTA complex is formed which reacts in a second step with the tripodal ligand 2,2',2' '-nitrilotris(ethanethiol) (NS3) or its carboxyl derivative NS3COOH (a) and the monodentate phosphine ligands (triphenylphosphine L1, dimethylphenylphosphine L2) or isocyanides (tert-butyl isonitrile L3, methoxyisobutyl isonitrile L4, 4-isocyanomethylbenzoic acid-L-arginine L5, 4-isocyanomethylbenzoic acid-L-arginyl-L-arginine L6, 4-isocyanomethylbenzoic acid-neurotensin(8-13) L7) to the so-called '4+1' complex. Copper(I) isocyanide complexes are used for preparing the '4+1' complexes. That facilitates storage stability and allows kit formulations, and, moreover, enables the formation of 188Re complexes in acidic solution. Only micromolar amounts of the monodentate ligand are needed, and that results in high specific activity labeling of interesting molecules. The lipophilicity of complexes can be controlled by introducing a carboxyl group into the tetradentate ligand and/or derivatization of the monodentate ligands. Furthermore, the carboxyl group enables the conjugation of biomolecules. As an example, the neurotensin derivative CN-NT(8-13) was prepared and labeled with 99mTc according to the '4+1' approach, and its behavior in vivo was studied.

In vivo measurement of the serotonin transporter with (S)-([18F]fluoromethyl)-(+)-McN5652.

The radiolabeled serotonin transporter (SERT) ligand [(11)C](+)-McN5652 has recently been used in clinical positron emission tomography (PET) studies for SERT imaging. However, this radioligand offers disadvantages in routine clinical settings because of its short radioisotope half-life (eg PET facilities within hospitals without a cyclotron need to acquire such radioligands from distant cyclotron units for clinical use). S-([(18)F]fluoromethyl)-(+)-McN5652 ([(18)F](+)-FMe-McN5652) is an analogue which has been synthesized newly, and has a significantly longer radioisotope half-life. In the porcine brain, it demonstrates the same characteristic distribution pattern of serotonin-uptake sites like the (11)C-labeled congener with the highest binding in the midbrain and thalamus and the lowest in the cerebellum and occipital cortex. It shows a 30% higher blood-brain transfer and a slower peripheral metabolism than [(11)C](+)-McN5652. Rather uniform brain binding was observed after injection of the pharmacologically inactive radiolabeled enantiomer, or after pretreatment with the highly selective SERT inhibitor citalopram. The norepinephrine uptake inhibitor maprotiline did not show any inhibitory effect. Using a one-tissue compartment model (K(1), k"(2)) or a two-tissue compartment model (K(1) to k(4)) with or without constraints for calculation, the regional binding parameters of [(11)C](+)-McN5652 and [(18)F](+)-FMe-McN5652 are highly correlated among each other and with the SERT density, as determined by in vitro binding of [(3)H]citalopram. Using constraints to correct for the free fraction and nonspecific binding of the radiotracers, a considerable increase of the midbrain-occipital cortex ratios with higher values for [(18)F](+)-FMe-McN5652 compared to [(11)C](+)McN5652 was revealed. It is concluded that [(18)F](+)-FMe-McN5652 has better features than [(11)C](+)McN5652 for SERT imaging with PET.