The effects of repeated brain MRI on chromosomal damage.

BACKGROUND: Magnetic resonance imaging (MRI) is currently considered a safe imaging technique because, unlike computed tomography, MRI does not expose patients to ionising radiation. However, conflicting literature reports possible genotoxic effects of MRI. We herein examine the chromosomal effects of repeated MRI scans by performing a longitudinal follow-up of chromosomal integrity in volunteers. METHODS: This ethically approved study was performed on 13 healthy volunteers (mean age 33 years) exposed to up to 26 3-T MRI sessions. The characterisation of chromosome damage in peripheral blood lymphocytes was performed using the gold-standard biodosimetry technique augmented with telomere and centromere staining. RESULTS: Cytogenetic analysis showed no detectable effect after a single MRI scan. However, repeated MRI sessions (from 10 to 20 scans) were associated with a small but significant increase in chromosomal breaks with the accumulation of cells with chromosomal terminal deletions with a coefficient of 9.5% (95% confidence interval 6.5-12.5%) per MRI (p < 0.001). Additional exposure did not result in any further increase. This plateauing of damage suggests lymphocyte turnover. Additionally, there was no significant induction of dicentric chromosomes, in contrast to what is observed following exposure to ionising radiation. CONCLUSIONS: Our study showed that MRI can affect chromosomal integrity. However, the amount of damage per cell might be so low that no chromosomal rearrangement by fusion of two deoxyribonucleic breaks is induced, unlike that seen after exposure to computed tomography. This study confirms that MRI is a safe imaging technique.

Imaging the aging brain: study design and baseline findings of the SENIOR cohort.

BACKGROUND: Current demographic trends point towards an aging society entailing increasing occurrence and burden of neurodegenerative diseases. In this context, understanding physiological aging and its turning point into neurodegeneration is essential for the development of possible biomarkers and future therapeutics of brain disease. METHODS: The SENIOR study represents a longitudinal, observational study including cognitively healthy elderlies aged between 50 and 70 years old at the time of inclusion, being followed annually over 10 years. Our multimodal protocol includes structural, diffusion, functional, and sodium magnetic resonance imaging (MRI) at 3 T and 7 T, positron emission tomography (PET), blood samples, genetics, audiometry, and neuropsychological and neurological examinations as well as assessment of neuronal risk factors. RESULTS: One hundred forty-two participants (50% females) were enrolled in the SENIOR cohort with a mean age of 60 (SD 6.3) years at baseline. Baseline results with multiple regression analyses reveal that cerebral white matter lesions can be predicted by cardiovascular and cognitive risk factors and age. Cardiovascular risk factors were strongly associated with juxtacortical and periventricular lesions. Intra-subject across-test variability as a measure of neuropsychological test performance and possible cognitive marker predicts white matter volume and is significantly associated with risk profile. Division of the cohort into subjects with a higher and lower risk profile shows significant differences in intra-subject across-test variability and volumes as well as cortical thickness of brain regions of the temporal lobe. There is no difference between the lower- and higher-risk groups in amyloid load using PET data from a subset of 81 subjects. CONCLUSIONS: We here describe the study protocol and baseline findings of the SENIOR observational study which aim is the establishment of integrated, multiparametric maps of normal aging and the identification of early biomarkers for neurodegeneration. We show that intra-subject across-test variability as a marker of neuropsychological test performance as well as age, gender, and combined risk factors influence neuronal decline as represented by decrease in brain volume, cortical thickness, and increase in white matter lesions. Baseline findings will be used as underlying basis for the further implications of aging and neuronal degeneration as well as examination of brain aging under different aspects of brain pathology versus physiological aging.

Validation of in vitro cell-based human blood-brain barrier model using clinical positron emission tomography radioligands to predict in vivo human brain penetration.

We have evaluated a novel in vitro cell-based human blood-brain barrier (BBB) model that could predict in vivo human brain penetration for compounds with different BBB permeabilities using the clinical positron emission tomography (PET) data. Comparison studies were also performed to demonstrate that the in vitro cell-based human BBB model resulted in better predictivity over the traditional permeability model in discovery organizations, Caco-2 cells. We evaluated the in vivo BBB permeability of [(18)F] and [(11)C]-compounds in humans by PET imaging. The in vivo plasma-brain exchange parameters used for comparison were determined in humans by PET using a kinetic analysis of the radiotracer binding. For each radiotracer, the parameters were determined by fitting the brain kinetics of the radiotracer using a two-tissue compartment model of the ligand-receptor interaction. Bidirectional transport studies with the same compounds as in in vivo studies were carried out using the in vitro cell-based human BBB model as well as Caco-2 cells. The in vitro cell-based human BBB model has important features of the BBB in vivo and is suitable for discriminating between CNS and non-CNS marketed drugs. A very good correlation (r(2) = 0.90; P < 0.001) was demonstrated between in vitro BBB permeability and in vivo permeability coefficient. In contrast, a poor correlation (r(2) = 0.17) was obtained between Caco-2 data and in vivo human brain penetration. This study highlights the potential of this in vitro cell-based human BBB model in drug discovery and shows that it can be an extremely effective screening tool for CNS programs.

Spatiotemporal decomposition in object-space along reconstruction in emission tomography.

Emission tomography has provided a new insight in brain mechanisms past years. Although reconstructions are nowadays mostly static, trend is going toward dynamic acquisitions and reconstructions. This opens a new range of investigations, for instance for drugs discovery. Indeed new drugs are studied through the dynamic ability of tissues to catch them. However, it is required to know radiotracer concentration of blood that irrigates tissues in order to draw conclusions on potentials of these drugs. This concentration is called 'input function' and this paper presents a new method for measuring it in a non-invasive way. Our new method relies on simultaneous estimations of vessels kinetics and vessels spatial distribution. These estimations are performed during the reconstruction process and take into account the statistical nature of measured signals. Indeed, this method is based on the maximisation of the likelihood of counts in detectors. It takes advantages of a non-negative matrix factorisation which separate spatial and temporal components. Results are very promising, since it estimates arterial input function accurately although object emits just a limited amount of photons, especially within the first minutes.

Guideline to regulations for radiopharmaceuticals in early phase clinical trials in the EU.

The purpose of this guideline is to help investigators by giving an overview of relevant current EU requirements concerning the quality of starting materials and final drug products (the radiopharmaceuticals), the non-clinical safety studies and dosimetry considerations whilst designing a human clinical trial which includes the use of radiopharmaceutical compounds.

Predicting plutonium decorporation efficacy after intravenous administration of DTPA formulations: Study of pharmacokinetic-pharmacodynamic relationships in rats.

PURPOSE: The objectives of this study were: 1) to assess the relationship between plutonium decorporation (increased excretion and reduced retention in main organs of deposition) induced by intravenous liposome formulations of the chelating agent diethylene triamine pentaacetic acid (DTPA) and its pharmacokinetics, and 2) to model the renal excretion of plutonium after treatment with liposome-encapsulated DTPA in order to predict its efficacy and to optimise treatment schedules. MATERIALS AND METHODS: Pharmacokinetic parameters from plasma or urinary data (days 0-16 sample collections) were modelled versus decorporation efficacy, and best correlations were selected for their goodness of fit. RESULTS: The plutonium decorporation enhancement by DTPA liposomal formulations was well described by logistic models and the best correlation was observed with the area under the DTPA concentration curve of each formulation. The plutonium urinary excretion rates decreased mono-exponentially as a function of time after a single dose and the proposed model allowed a simple determination of the elimination half-life of the Pu-DTPA complex, a reasonably good approximation of the long-term efficacy of the treatments from truncated urinary data. CONCLUSIONS: Both liposomal formulations of chelating agents and pharmacokinetic approaches to plutonium decorporation should be helpful in optimising treatment protocols.

Pharmacokinetics of DTPA entrapped in conventional and long-circulating liposomes of different size for plutonium decorporation.

The aim of the present study was to develop an efficient DTPA liposome formulation designed for plutonium decorporation. DTPA was encapsulated in conventional (CL) and polyethylene glycol-coated stealth liposomes (SL) prepared by extrusion followed by the freeze-thawing method and sizing from around 100 to 800 nm. DTPA encapsulation percentages were approximately 30% in CL of any size but dropped from 48% to 7% as the diameter of SL was reduced. The pharmacokinetics of [(14)C]-DTPA encapsulated in large and small vesicles was evaluated in rats after a single intravenous administration. Both liposomal composition and size reduction had a significant impact on pharmacokinetic parameters, inducing a marked increased in exposure of the body to DTPA and its delayed excretion. DTPA distribution was moderate in liver but enhanced in spleen and bone and was dose-dependent, especially when SL of 100 nm were given. In conclusion, small and stealth(R) vesicles have interesting properties in delivering DTPA to contaminated tissues.

In vivo imaging of human cerebral nicotinic acetylcholine receptors with 2-18F-fluoro-A-85380 and PET.

UNLABELLED: 2-(18)F-fluoro-3-[2(S)-2-azetidinylmethoxy]pyridine (2-(18)F-fluoro-A-85380) is a PET radioligand that is specific for nicotinic acetylcholine receptors (nAChRs) and has a high affinity for the alpha(4)beta(2) subtype. The purpose of this study was to evaluate different strategies to quantify 2-(18)F-fluoro-A-85380 binding in healthy nonsmoking human volunteers. METHODS: After intravenous injection of 189 +/- 30 MBq (0.8-5.7 nmol) of 2-(18)F-fluoro-A-85380, the first dynamic PET scan was acquired over 150 min. The second 30-min PET scan was performed 60 min later. Time-activity curves were generated from volumes of interest. 2-(18)F-Fluoro-A-85380 volume of distribution (DV) was quantified using compartmental kinetic analysis and Logan graphical analysis. In the kinetic analysis, the 1-tissue compartment model (1TCM) and the 2-tissue (2TCM) compartment model were applied. The most appropriate kinetic model was determined using the Akaike Information Criterion. The effect of reducing the PET study duration on the reliability of the DV values computed by the kinetic and the graphical analyses was evaluated. RESULTS: Time-activity curves were better described by the 2TCM. The DV values ranged from 5.2 +/- 0.5 in the occipital cortex, 6.2 +/- 0.2 in the frontal cortex, and 7.3 +/- 0.4 in the putamen to 15.4 +/- 2.1 in the thalamus. These regional DV values were consistent with the distribution of nAChRs in the human brain. Logan graphical analysis provided slightly lower DV values than those of the 2TCM (from -3.5% in the occipital cortex to -6.6% in the thalamus). The minimal study duration required to obtain stable DV estimates in all regions was similar for the 2 methods: 140 min for the 2TCM and 150 min for the Logan analysis. DV estimates obtained with the 2TCM were more stable than those calculated by the Logan approach for the same scan duration. CONCLUSION: These results show that 2-(18)F-fluoro-A-85380 can be used to assess nAChRs binding in the human brain with PET.

Characterization of a synthetic anionic vector for oligonucleotide delivery using in vivo whole body dynamic imaging.

PURPOSE: To compare the pharmacokinetics and bioavailability of an oligonucleotide delivered in a free form or using cationic or anionic synthetic carrier systems. METHODS: Whole body dynamic quantitative imaging and metabolism of a HIV antisense oligonucleotide intravenously administered either free or incorporated into synthetic carriers were compared in baboons. using non invasive positron emission tomography and an enzyme-based competitive hybridization assay, respectively. RESULTS: In its free form, the oligonucleotide showed high liver and kidney concentration, rapid plasmatic degradation and elimination from the body. Use of a cationic vector slightly protected the oligonucleotide against degradation and enhanced uptake by the reticulo-endothelial system. In contrast, the anionic vector dramatically enhanced the uptake in several organs, including the lungs, spleen and brain, with a prolonged accumulation of radioactivity in the brain. Using this vector, intact oligonucleotide was detected in plasma for up to two hours after injection. and the T 1/2beta and distribution volume increased by 4- and 7-fold, respectively. No evidence of toxicity was found after a single dose administration. CONCLUSIONS: The anionic vector improves significantly the bioavailability and the pharmacokinetics of the oligonucleotide, and is a promising delivery system for in vivo administration of therapeutic nucleic acids.

Anti-cancer drug diffusion within living rat brain tissue: an experimental study using [3H](6)-5-fluorouracil-loaded PLGA microspheres.

This study was performed (i) to monitor the diffusion of the anti-cancer drug 5-fluorouracil (5-FU) and (ii) to elucidate the fate of poly(lactide-co-glycolide) (PLGA) based microspheres within living rat brain tissue upon intracranial implantation. Drug-loaded microparticles were prepared using a solvent emulsion/extraction process and administered into healthy and C6 glioma-bearing Sprague-Dawley rats. The same surgical procedure was carried out with magnetite-loaded microspheres. To monitor 5-FU diffusion from the implantation site, tissue combustion was performed on animals implanted with tritiated drug microspheres. T2-weighted nuclear magnetic resonance imaging was undertaken on animals implanted with magnetite-loaded microspheres to determine microsphere localization after deposit. Results show that an important microparticle backflow occurs in healthy rats, whereas the microspheres remain at the site of administration in C6 glioma-bearing rats. Drug diffusion is limited to the vicinity of the implantation site.

Intravitreal delivery of oligonucleotides by sterically stabilized liposomes.

PURPOSE: The efficacy of sterically stabilized liposomes for delivering a model phosphodiester oligonucleotide intravitreally was investigated in the rabbit. METHODS: Ocular distribution and clearance from the vitreous humor of a model 16-mer oligothymidylate (pdT16) were evaluated in the rabbit by radioactivity measurements after intravitreal injection of either a solution or liposomes containing the [33P]pdT16 oligonucleotide. The integrity of pdT16 was investigated using a competitive hybridization assay. RESULTS: The residual concentration of the [33P]pdT16 oligonucleotide within the ocular tissues was significantly increased after intravitreal administration of the liposomal suspension compared with a simple solution. Administration of liposome-encapsulated pdT16 oligonucleotide resulted in sustained release into the vitreous and the retina-choroid compared with release from the solution and in a reduced distribution to nontarget tissues (sclera, lens). In addition, liposomes protected the phosphodiester oligonucleotide against degradation. This was not observed after administration of the free oligonucleotide. CONCLUSIONS: The intravitreal injection of a phosphodiester oligonucleotide encapsulated within liposomes is a new way of delivering intact oligonucleotide to the eye in a controlled manner. This offers interesting prospects for the treatment of retinal diseases.

Early detection of chemoresistance in vivo through the use of a radiolabeled antisense oligonucleotide.

AIMS: Radiolabeled antisense oligonucleotide to target the mRNA of the hmdr1 gene for diagnostic purposes is a new concept for evaluating the chemoresistance of tumors in vivo. METHODS AND RESULTS: An 18 mer complementary to the zone which contains the translation initiation codon of the hmdr1 gene was modified using one phosphoramidate group and one dimethoxytrityle group at the 5' and 3'ends. It permitted probe radiolabeling by 125I. Chemical modifications made to the antisense probe ensured the stability in biological media tested by incubation with human serum at 37 degrees C from 5 minutes to 24 hours. These modifications did not interfere with recognition of the target. Retention of the antisense probe followed the expression level of the target transcript in in vitro and in vivo studies. In vitro, after a 2-hour incubation in the presence of K562--sensitive (S) and- resistant (R) cell lines, uptake was respectively 4.27 +/- 0.96% ID/mg protein and 7.78 +/- 0.46% ID/mg protein (p < 0.001). In vivo, the ratios between radioactivity found in the tumor and that found in the striated muscle and in the blood were, respectively, 20 and 3 for IGR OV1 resistant tumor and 1 and 0.3 for the sensitive one. CONCLUSION: In our study, resistant cell lines and tumor showed greater retention of the specific probe than the sensitive ones. This constitutes a further advance towards non invasive imaging of resistant genes involved in chemoresistance. These results are encouraging: the current trend in innovative cancer therapy is moving towards targeting the genes of interest.