Biomedical subjects

Helmut Viernstein

Publications and source records attributed to Helmut Viernstein.

17 recordsLinked to original sources

PubMed2006

[18F]FETO: metabolic considerations.

PURPOSE: 11beta-Hydroxylase is a key enzyme in the biosynthesis of adrenocortical steroid hormones and is a suitable target for the imaging of the adrenal cortex. [(11)C]Metomidate (MTO), [(11)C]etomidate (ETO) and desethyl-[(18)F]fluoroethyl-etomidate (FETO) are potent inhibitors of this enzyme and are used for PET imaging of adrenocortical pathologies. The aims of this study were (1) to evaluate and compare the metabolic stability of MTO, ETO and FETO against esterases and (2) to investigate the metabolic pattern of FETO in vivo. METHODS: In vitro assays were performed using different concentrations of MTO, ETO and FETO with constant concentrations of carboxylesterase. Human in vivo studies were performed with human blood samples drawn from the cubital vein. After sample clean-up, the serum was analysed by HPLC methods. RESULTS: In vitro assays showed Michaelis-Menten constants of 115.1 mumol for FETO, 162.0 mumol for MTO and 168.6 mumol for ETO. Limiting velocities were 1.54 mumol/min (FETO), 1.47 mumol/min (MTO) and 1.35 mumol/min (ETO). This implies insignificantly decreased esterase stability of FETO compared with MTO and ETO. In vivo investigations showed a rapid metabolisation of FETO within the first 10 min (2 min: 91.41%+/-6.44%, n=6; 10 min: 23.78%+/-5.54%, n=4) followed by a smooth decrease in FETO from 20 to 90 min (20 min: 11.23%+/-3.79% n=4; 90 min: 3.68%+/-3.65%, n=4). Recovery rate was 61.43%+/-3.19% (n=12). CONCLUSION: In vitro experiments demonstrated that FETO stability against esterases is comparable to that of ETO and MTO. The metabolic profile showed that FETO kinetics in humans are fast.

Humans↗

PubMed2006

Uptake of bone-seekers is solely associated with mineralisation! A study with 99mTc-MDP, 153Sm-EDTMP and 18F-fluoride on osteoblasts.

PURPOSE: Although polyphosphonates (PPs) were introduced as bone imaging agents in nuclear medicine in the early 1970s, the mechanisms involved in their uptake still remain unclear. Suggested mechanisms range from mineral adsorption with disputed binding to the organic phase, over incorporation into the mineralisation process to a combination of both mechanisms. Thus, our investigations aimed to: (1) evaluate adsorption parameters of (99m)Tc-MDP, (153)Sm-EDTMP and (18)F-fluoride on mineralising osteoblast cultures, (2) correlate the radiotracer binding measured in the cell cultures with binding values from our previously presented mineral model and (3) compare binding with cell number. METHODS: Primary osteoblasts were obtained by sequential digestion of foetal mice calvariae. The cells were incubated with 0.3 mumol of radiolabelled PPs or 25 MBq (18)F-fluoride for 120 min. Gamma signals from labelled samples were detected with a Millennium Hawkeye SPECT camera or with a dedicated Advance full-ring PET scanner and the binding percentages were calculated. RESULTS: From days 8 to 15 of culture, the percent binding of all evaluated tracers increased significantly, whereas the protein concentration showed insignificant changes. Additional comparisons of the binding values with our recently published pre-vivo model revealed remarkable agreement, suggesting solely bone-forming minerals to be responsible for radiotracer binding. CONCLUSION: This study provides evidence that binding of the evaluated radiotracers is not associated with osteoblast numbers but only with the concentration of bone-forming minerals. The presented correlations substantiate our recently presented pre-vivo model for the evaluation of bone-seekers: mechanisms associated with the uptake of bone-seekers are irreversible and mineral-associated processes.

Adsorption↗

PubMed2006

In vitro evaluation of no carrier added, carrier added and cross-complexed [90Y]-EDTMP provides evidence for a novel "foreign carrier theory".

The present study focused on the preparation of novel bone tracers containing yttrium as radionuclide or carrier. Moreover, these preparations were comparatively evaluated in vitro on the basis of a recently presented pre vivo model comprising binding studies on synthetic and human bone powder. It was shown that among the therapeutic radionuclides, no carrier added [(90)Y]-EDTMP exceeded [(188)Re]-EDTMP while yielding lower binding values than [(153)Sm]-EDTMP. Furthermore, the authors investigated the influence of "foreign" carriers added to [(90)Y]-EDTMP, [(99m)Tc]-EDTMP and [(111)In]-EDTMP by the method of cross-complexation. The findings reveal a new paradigm: a carrier more foreign to the complexed radionuclide causes a higher binding increase on human bone matrices in vitro than a more "related" carrier.

Bone and Bones↗

PubMed2005

Validation of fluid bed granulation utilizing artificial neural network.

Three innovative components (an annular gap spray system, a booster bottom and an outlet filter) have been developed by Innojet Technologies to improve fluid bed technology and to reduce the common interference factors (clogging of nozzles and outlet filters, spray loss, spray drying and fluidized bed heterogeneity). In a fluid bed granulator, three conventional components have been replaced with these innovative components. Validation of the modified fluid bed granulator has been conducted using a generalized regression neural network (GRNN). Under different operating conditions (by variation of inlet air temperature, liquid-binder spray rate, atomizing air pressure, air velocity, amount and concentration of binder solution and batch size), sucrose was granulated and the properties of size, size distribution, flow rate, repose angle and bulk and tapped volumes of granules were measured. To confirm the method's validity, the trained network has been used to predict new granulation parameters as well as granule properties. These forecasts were then compared with the corresponding experimental results. Good correlation has been obtained between the predicted and the experimental data. From these findings, we conclude that the GRNN may serve as a reliable method to validate the modified fluid bed apparatus.

Chemistry, Pharmaceutical↗

PubMed2005

Synthesis and biodistribution of [18F]FE@CIT, a new potential tracer for the dopamine transporter.

In the last decade radiolabeled tropane analogs based on beta-CIT have proven indispensable for the imaging of the dopamine transporter. However, further improvements in their pharmacodynamic and pharmacokinetic features are desirable. An important improvement, yielding in higher affinity to the dopamine transporter (DAT) vs. serotonin transporter (SERT), can be achieved by a simple replacement of the carboxylic methyl ester group in beta-CIT by a fluoroethyl ester. The preparation and ex vivo evaluation of this new beta-CIT-analog ([18F]FE@CIT) is presented here. Precursor and standard were prepared from beta-CIT and analyzed by spectroscopic methods. Yields of precursor and standard preparation were 61% and 42%, respectively. [18F]FE@CIT was prepared by distillation of [18F]bromofluoroethane ([18F]BFE) and reaction with (1R-2-exo-3-exo)8-methyl-3-(4-iodo-phenyl)-8-azabicyclo[3.2.1] octane-2-carboxylic acid. After 10 min at 150 degrees C the product was purified using a C-18 SepPak. The radiosynthesis evinced radiochemical yields of >90% (based on [18F]BFE), the specific radioactivity was >416 GBq/micromol. An average 30 microAh cyclotron irradiation yielded more than 2.5 GBq [18F]FE@CIT. For the ex vivo bioevaluation, 20 male Sprague-Dawley rats were sacrificed at 5, 15, 30, 60, and 120 min after injection. Organs were removed, weighed, and counted. For autoradiographic experiments, transverse brain slices of about 100 microm were prepared. The ex vivo evaluation showed highest brain uptake in striatal regions, followed by thalamus and cerebellum. The highest striatum to cerebellum ratio was 3.73 and the highest thalamus to cerebellum ratio was 1.65. Autoradiographic images showed a good and differentiated uptake in striatal regions with a good target-to-background ratio.

Animals↗

PubMed2005

New aspects on the preparation of [11C]Methionine--a simple and fast online approach without preparative HPLC.

At present, most data available on PET imaging of brain tumors using amino acids are based on l-[S-methyl-11C]methionine (MET). This radiopharmaceutical accurately delineates tumor extent, sometimes even better than CT. Since MET is playing such an important role for PET, a potent preparation method for this radiotracer allowing frequent syntheses for PET routine is desirable. Therefore, a simple disposable synthesis module was conceived without HPLC purification. Using a solid supported [11C]methylation on Al2O3 leads to the simplification of the preparation requiring only filtration for separation of precursor and MET. The presented method is able to produce high purity MET in excellent yields enough to serve several consecutive patients.

Brain Neoplasms↗

PubMed2005

Binding studies of [18F]-fluoride and polyphosphonates radiolabelled with [99mTc], [111In], [153Sm] and [188Re] on bone compartments: verification of the pre vivo model?

INTRODUCTION: Although the first polyphosphonates (PP) were introduced to nuclear medicine as bone imagers in the early 70s, mechanisms involved in uptake still remain speculative. Controversies range from adsorption onto the mineral phase with disputed binding to the organic phase, over incorporation into the mineralisation process to a combination of both mechanisms. Other factors such as solubility of the complex, concentration of ligand or effects of the radionuclide have also been discussed as possible parameters influencing bone uptake. Therefore, the present work aimed to verify the recently presented pre vivo model which was developed to rate the influence of various factors on the binding of differently radiolabelled PP and [18F]-fluoride on synthetic bone matrix. METHODS: Radiolabelled polyphosphonates and [18F]-fluoride were added to a vial containing lyophilised and milled spongiosa (Sp) or cortical bone (Co) in Hank's Balanced Salt Solution. After incubation, the radioactivity was measured in the gamma-counter before and after filtration. The percentage of irreversibly bound radioactivity was calculated. Same experiments were performed after decalcification of Sp and Co with hydrochloric acid. RESULTS: Descriptively, [111In] increases the uptake of EDTMP in each case compared to similarly prepared [(99m)Tc]-analogues: [111In]-EDTMP > [(99m)Tc]-EDTMP, [111In]-/In-EDTMP > [(99m)Tc]-/In-EDTMP and [111In]-/Re-EDTMP > [(99m)Tc]-/Re-EDTMP. [188Re]-EDTMP shows higher binding than the carrier-added analogue, contradicting recent in vivo findings of [(188)Re]-PP. However, our findings on human matrix are consistent with those of a previous study using artificial bone material. Binding on decalcified tissue was very low (PP) to moderate ([18F]-fluoride) and reversible. Remarkable is also the unrivalled high uptake of [18F]-fluoride, showing no reduced uptake on Co and Sp as compared to hydroxyapatite (HA) and amorphous calcium phosphate (ACP). CONCLUSION: The binding of the evaluated bone seekers on these human bone matrices follows a comparable pattern as on artificial bone. The present study substantiates the fact that binding predominantly occurs on the inorganic compartment of bone. The best correlation was found between HA and Co. Therefore, HA can serve as a matrix for representative binding studies.

Bone and Bones↗

PubMed2004

Labelling of EDTMP (Multibone) with [111In], [99mTc] and [188Re] using different carriers for "cross complexation".

Detection and follow up of bone metastases are important in diagnostic nuclear medicine. However, although the methods are well established, the mechanisms involved in the bone uptake of radiotracers still remain speculative. The aim of the present study was the evaluation and comparison of the labelling of EDTMP with different radionuclides (n.c.a. = no carrier added) and different carriers (c.a. = carrier added). Since different nuclides have an impact on the radiochemical and biological properties of the tracer, our experiments were designed to further elucidate the mechanisms and structural prerequisites for bone uptake. We labelled the commercially available Multibone kit with [111In] and [99mTc] using different carriers, e.g. indium and rhenium, to form "cross complexes". In the case of [188Re] we compiled minor modifications to this kit for the first time allowing the simple preparation of [188Re]-EDTMP in the departments without on-site radiopharmacy.

Indium Radioisotopes↗

PubMed2004

New aspects on the preparation of [11C]acetate--a simple and fast approach via distillation.

[11C]Acetate, initially developed for nuclear cardiology has gained increased interest also for oncological problems. A conjoint problem of all preparation methods is the high sensitivity of the Grignard-precursor to moisture, demanding long cleaning and drying procedures of apparatus and reaction vials. Our rationale was to simplify and accelerate the preparation of [11C]acetate by the development of an inert, sterile and disposable system. The present publication deals with the remote-controlled preparation of [11C]acetate via distillation into a buffer ready to use.

Acetates↗

PubMed2004

Binding studies of [(18)F]-fluoride and polyphosphonates radiolabelled with [(111)In], [(99m)Tc], [(153)Sm], and [(188)Re] on bone compartments: a new model for the pre vivo evaluation of bone seekers?

INTRODUCTION: Although the first polyphosphonates were already introduced in the early 1970s, mechanisms involved in uptake still remain speculative. The present work aimed to establish a new method to rate the influence of various factors on the uptake and to evaluate new bone-seekers on these bone compartments. METHODS: Radioactive-labelled diphosphonates and [(18)F]-fluoride were added to a vial containing hydroxyapatite (HA), collagen, or amorphous calcium phosphate (ACP) in 3 ml of Hanks' Balanced Salt Solution (HBSS). After incubation, these suspensions were filtered, the radioactivity was measured in the gamma-counter, and the percentage of irreversibly bound radioactivity was calculated. RESULTS: Kinetic experiments revealed uptake increase over time for [(99m)Tc]-MDP and [(18)F]-fluoride on various amounts of matrix. After 120 min, static studies on HA yielded: [(99m)Tc]-EDTMP < [(188)Re]-/Re-EDTMP < [(99m)Tc]-/11 microl Re-EDTMP < [(99m)Tc]-/In-EDTMP < [(99m)Tc]-/15 microl Re-EDTMP < nca [(188)Re]-EDTMP < [(111)In]-/Re-EDTMP < [(111)In]-EDTMP < [(111)In]-/In-EDTMP < [(99m)Tc]-DPD < [(99m)Tc]-/80 microl Re-EDTMP < [(99m)Tc]-EDTMP "boiled" < [(99m)Tc]-/150 microl Re-EDTMP < [(153)Sm]-EDTMP < [(99m)Tc]-/11 microl Re-EDTMP "boiled" < [(18)F]-ions < [(99m)Tc]-MDP. Collagen showed very low uptake. Reincubation experiments suggest that bone tracers are irreversibly bound. CONCLUSION: The presented method is rapid and feasible to examine the adsorption of radioactive-labelled substances on bone components. Correlations between our findings and published in vivo data support the application as a simple model.

Bone Neoplasms↗

PubMed2004

Biological evaluation of 2'-[18F]fluoroflumazenil ([18F]FFMZ), a potential GABA receptor ligand for PET.

[(11)C]Flumazenil, a highly selective benzodiazepine antagonist is the most extensively used GABA(A) ligand for PET so far. To overcome half life disadvantages of (11)C a [(18)F]-labeled flumazenil derivative, 2'-[(18)F]fluoroflumazenil (FFMZ) was developed and biologically evaluated with respect to the GABA(A) receptor. Organ with the highest uptake was the pituitary gland. Brain uptake was high and followed the order cortex>thalamus>cerebellum>rest brain. Fluoroflumazenil displaced [(3)H]flumazenil binding from membrane GABA(A) receptors with an IC(50)value (3.5 nM) comparable to that of Flumazenil (2.8 nM). The presented data confirm the potential of [(18)F]FFMZ for PET imaging of the GABA-ergic system.

Animals↗

PubMed2003

In vivo and in vitro evaluation of [18F]FETO with respect to the adrenocortical and GABAergic system in rats.

11beta-Hydroxylase (CYP11B1, P45011beta) plays an important role in the biosynthesis of cortisol and aldosterone and has been shown to be a good target for the in vivo imaging of adrenocortical incidentalomas in nuclear medicine. [11C]Metomidate (MTO), a potent inhibitor of this enzyme, is used for positron emission tomography (PET) imaging of adrenocortical pathology. The synthesis of (R)-1-(1-phenylethyl)-1H-imidazole-5-carboxylic acid 2-[18F]fluoroethylester (FETO), a close analogue to MTO and etomidate (ETO), has been presented recently, and the present investigation aimed to characterise the in vivo distribution of FETO. Since ETO is a well-known anaesthetic drug acting via the GABAergic system, the interaction of FETO with GABAA receptors was also evaluated. Eighteen male Sprague-Dawley rats were injected with 1.73-3.06 MBq of FETO into a tail vein after venodilatation in a 40 degrees C water bath. Rats were sacrificed by exsanguination from the abdominal aorta under deep ether anaesthesia after 10 (n=6), 30 (n=6) or 60 min (n=6); organs were removed, weighed and counted. For binding experiments, rat cerebellar membranes were incubated for 90 min at 4 degrees C in TC-50 buffer, 150 mM NaCl and 2 nM of [3H]flunitrazepam in the absence or presence of 10 microM diazepam or various concentrations of ETO, MTO and FETO. In vivo evaluation evinced very high uptake in the adrenal glands (7.52%+/-1.19% ID/g at 30 min), followed by lung (1.18%+/-0.19% ID/g, 10 min), liver (0.59%+/-0.13% ID/g, 10 min) and duodenum (0.7%+/-0.29% ID/g, 60 min). No defluorination nor fluoroethyl-ester cleavage was observed. When brain regions were compared with the thalamus (the reference region), highest relative uptake was seen in the cortex (2.34), followed by "rest brain" (2.13) and cerebellum (1.96). FETO and ETO were able to increase the binding of [3H]flunitrazepam with similar potencies and to a comparable extent. It is concluded that FETO shows characteristics suitable for the imaging of adrenocortical pathology with PET. Binding experiments on GABA receptors demonstrate a comparable effect of FETO and ETO. Hence, FETO possibly could also be used to elucidate the function, dynamics and kinetics of narcotic drugs with PET.

Adrenal Cortex↗

PubMed2003

Molecular dynamics simulations of beta-cyclodextrin in aqueous solution.

Molecular dynamics (MD) simulations of beta-cyclodextrin (beta-CD) have been carried out in aqueous solution at 300 K over a period of about 200 ps using Tripos force field. The atomic trajectories obtained by these simulations have been analysed by means of the occurrence of hydrogen bonds. The MD simulations lead to an association of seven water molecules into the beta-CD cavity which is in a good agreement with X-ray crystallography experiments. This demonstrates that the force field used in the simulations is able to reproduce the experimentally observed hydrophilic-hydrophobic characteristics of beta-CD molecule.

Crystallography, X-Ray↗

PubMed2003

Solubility enhancement of low soluble biologically active compounds--temperature and cosolvent dependent inclusion complexation.

The solubility enhancement of biologically active compounds was analysed in dependence on temperature, amount of cosolvents and on beta-cyclodextrin as complexing agent. The analysis was performed for the systemic fungicide triflumizole (TF), a poorly water soluble compound. All parameters lead to an improvement of the solubility, the largest effect was obtained for host-guest complexation with beta-cyclodextrin. Generally, the combination of cosolvents and beta-cyclodextrin does not increase the solubility of the compound, because cosolvents destabilize the inclusion complex. At higher cosolvent concentrations the solubility of TF is mainly determined by the solubility of the free non-complexed compound in the solvent mixtures. Raising temperature enhances the solubility in any cases. It could be shown that the temperature dependence of the solubility of TF is controlled by the solubility in the solvent mixtures and not by the inclusion reaction.

Cyclodextrins↗

PubMed2002

Protein fingerprinting of Saccharomyces isolates with therapeutic relevance using one- and two-dimensional electrophoresis.

In therapeutic products and preparations Saccharomyces cerevisiae is used because of its nutritive properties. Moreover, so called Saccharomyces boulardii yeasts are used in the prevention and treatment of several types of diarrhea. Taxonomically however, S. boulardii is not accepted as a distinct species. The protein fingerprint obtained after sodium dodecyl sulfate-polyacrylamide gel electrophoresis was identical for all isolates and therefore confirmed the designation of S. boulardii to the species S. cerevisiae. In contrast, using native polyacrylamide gel electrophoresis, 12 different protein fingerprints were detected, and allowed grouping of the product isolates. The spot patterns obtained by two-dimensional electrophoresis revealed a large degree of resemblance, however, small qualitative expression differences could be detected as well. Firstly, a spot having an isoelectric point of approximately 6 and 30 kDa could not be detected in S. boulardii yeasts. Secondly, nine different formations of spots occurred in the region around 16 kDa and pH 6. Therefore, on the one hand, it could be demonstrated that all of the product isolates belong to the same species, and on the other hand, it was possible to extensively subdivide the strains. In particular, two-dimensional electrophoresis allowed clustering of so called S. boulardii strains within the species S. cerevisiae.

Electrophoresis, Gel, Two-Dimensional↗

PubMedDate not supplied

The labelling of Nanocoll with [111In] for dual-isotope scanning.

UNLABELLED: Visualization and biopsy of sentinel lymph nodes play an important role in planning and controlling the therapy of breast cancer. Hitherto two methods-scintigraphy or gamma probe detection after injection of [99mTc]-nanocolloids and visual detection after injection of patent blue dye-are used routinely. There are no conclusive publications elucidating such important parameters as injection site, injection method and colloidal parameters. The present work aims to label Nanocoll with [111In] to provide an alternative method, a simultanous one-compound dual-isotope application. METHODS: [111In]-Indiumchloride was buffered with acetate and transferred to the nanocolloid. The colloid labelling reaction was complete after 30 min and filtrated through 100 nm Nuclepore filters. RESULTS: Incorporation yield of [111In]-Indium into the nanocolloid was nearly quantitative, the step associated with the major loss of activity was the particle sizing with a mean yield of 55%. CONCLUSION: The presented method allows for the routine supply of [111In]-nanocolloids. Size-filtered [111In]-Nanocoll shows the same particle size range as [99mTc]-Nanocoll.

Indium Radioisotopes↗

PubMedDate not supplied

Comparison of three different purification methods for the routine preparation of [11C] Metomidate.

PET with (R)-[O-methyl-11C] metomidate ([11C] MTO) is an attractive method for the characterisation of adrenal masses discriminating lesions of adrenal cortical origin from noncortical lesions. [11C] MTO was prepared by the reaction of [11C] methyliodide with the corresponding free acid. Three purification methods have been compared. The method of choice uses preparative HPLC with a ready-to-use weak acidic solvent.

Adrenal Gland Neoplasms↗