Microvasculature alters the dispersion properties of shear waves--a multi-frequency MR elastography study.

Magnetic Resonance Elastography (MRE) uses macroscopic shear wave propagation to quantify mechanical properties of soft tissues. Micro-obstacles are capable of affecting the macroscopic dispersion properties of shear waves. Since disease or therapy can change the mechanical integrity and organization of vascular structures, MRE should be able to sense these changes if blood vessels represent a source for wave scattering. To verify this, MRE was performed to quantify alteration of the shear wave speed cs due to the presence of vascular outgrowths using an aortic ring model. Eighteen fragments of rat aorta included in a Matrigel matrix (n=6 without outgrowths, n=6 with a radial outgrowth extent of ~600 µm and n=6 with ~850 µm) were imaged using a 7 Tesla MR scanner (Bruker, PharmaScan). High resolution anatomical images were acquired in addition to multi-frequency MRE (ν = 100, 115, 125, 135 and 150 Hz). Average cs was measured within a ring of ~900 µm thickness encompassing the aorta and were normalized to cs0 of the corresponding Matrigel. The frequency dependence was fit to the power law model cs ~ν(y). After scanning, optical microscopy was performed to visualize outgrowths. Results demonstrated that in presence of vascular outgrowths (1) normalized cs significantly increased for the three highest frequencies (Kruskal-Wallis test, P = 0.0002 at 125 Hz and P = 0.002 at 135 Hz and P = 0.003 at 150 Hz) but not for the two lowest (Kruskal-Wallis test, P = 0.63 at 100 Hz and P = 0.87 at 115 Hz), and (2) normalized cs followed a power law behavior not seen in absence of vascular outgrowths (ANOVA test, P < 0.0001). These results showed that vascular outgrowths acted as micro-obstacles altering the dispersion relationships of propagating shear waves and that MRE could provide valuable information about microvascular changes.

Evaluation of Functionalized Polysaccharide Microparticles Dosimetry for SPECT Imaging Based on Biodistribution Data of Rats.

PURPOSE: Technetium-99 m (Tc-99 m)-labelled microparticles, functionalized with fucoidan to present a high affinity for P-Selectin, or [(99m)Tc] MP-fucoidan, were developed as a novel SPECT radiotracer for abdominal aortic aneurysm (AAA). As a prerequisite step forwards a clinical trial, the biodistribution and dosimetry of these [(99m)Tc] MP-fucoidan microparticles were performed in rats in order to estimate the absorbed and effective dose in humans. PROCEDURES: Microparticles with a maximum hydrodynamic diameter of 4 µm were obtained by crosslinking polysaccharides dextran and pullulan. They were functionalized with fucoidan then radiolabelled with Tc-99 m. A mean labelling efficiency of 92 ± 1% was measured. [(99m)Tc] MP-fucoidan (43 ± 2 MBq) was injected to 24 rats via the penis vein. Rats were euthanized at 30, 60, 120 and 240 min after injection (4 rats at each time point). Samples of each organ, as well as the injected microparticle suspensions, were aliquoted for counting. Four animals were sacrificed for blood clearance studies and four were sacrificed for image analysis and quantification of the cortical, medullary, papillary kidney, and pelvis uptake. A compartmental model was realised using SAAM II and organ data were fitted. The area under the curve was then used to compute the residence times in each rat organs and converted to human residence time values. Absorbed and effective human doses in organs were estimated using (1) the OLINDA/EXM 1.1 software with the hermaphroditic mathematical phantoms and (2) the OEDIPE software associated to the MCNPX Monte Carlo code and the ICRP reference computational male and female phantoms, using the updated tissue weighting factors in the ICRP Publication 103. RESULTS: The highest human residence times were found in the liver, kidneys, and urinary bladder wall. The largest doses were found in the kidneys and then in the urinary bladder wall and liver. The human effective doses were 6.06 µSv/MBq for the hermaphroditic mathematical phantom and 5.95 µSv/MBq for the ICRP adult reference computational phantom. CONCLUSIONS: Animal-based human dose estimates support a future first-in-human testing of [(99m)Tc] MP-fucoidan following IV injection.

Preclinical validation of 99mTc-annexin A5-128 in experimental autoimmune myocarditis and infective endocarditis: comparison with 99mTc-HYNIC-annexin A5.

Hydrazinonicotinamide-annexin A5 (HYNIC-Anx), a 99m technetium (99mTc)-labeled agent targeting phosphatidylserine, proved to be sensitive for the detection of apoptosis and thrombosis but is no longer available for clinical use. A mutant of human annexin designed for direct 99mTc labeling (referred to as Anx A5-128) showed improved binding affinity to phosphatidylserine and is expected to be used in humans. We compared both radiotracers with regard to pharmacokinetics and diagnostic ability in animal models. Biodistribution studies were performed in normal rats. Radiolabeled Anx A5-128 and HYNIC-Anx were compared in cardiovascular settings involving phosphatidylserine expression: experimental autoimmune myocarditis and infective endocarditis. Initial blood clearance was faster for Anx A5-128 than for HYNIC-Anx, and tissue biodistribution was similar overall for both tracers. The diagnostic sensitivity of Anx A5-128 was excellent and comparable to that of HYNIC-Anx. Anx A5-128 showed biodistribution and diagnostic ability similar to those of the HYNIC-Anx derivative, supporting its translation to clinical use.

Abdominal aortic aneurysms targeted by functionalized polysaccharide microparticles: a new tool for SPECT imaging.

Aneurysm diagnostic is nowadays limited by the lack of technology that enables early detection and rupture risk prediction. New non invasive tools for molecular imaging are still required. In the present study, we present an innovative SPECT diagnostic tool for abdominal aortic aneurysm (AAA) produced from injectable polysaccharide microparticles radiolabeled with technetium 99m ((99m)Tc) and functionalized with fucoidan, a sulfated polysaccharide with the ability to target P-Selectin. P-Selectin is a cell adhesion molecule expressed on activated endothelial cells and platelets which can be found in the thrombus of aneurysms, as well as in other vascular pathologies. Microparticles with a maximum hydrodynamic diameter of 4 µm were obtained by crosslinking the polysaccharides dextran and pullulan. They were functionalized with fucoidan. In vitro interactions with human activated platelets were assessed by flow cytometry that demonstrated a specific affinity of fucoidan functionalized microparticles for P-Selectin expressed by activated platelets. For in vivo AAA imaging, microparticles were radiolabeled with (99m)Tc and intravenously injected into healthy and AAA rats obtained by elastase perfusion through the aorta wall. Animals were scanned by SPECT imaging. A strong contrast enhancement located in the abdominal aorta of AAA rats was obtained, while no signal was obtained in healthy rats or in AAA rats after injection of non-functionalized control microparticles. Histological studies revealed that functionalized radiolabeled polysaccharide microparticles were localized in the AAA wall, in the same location where P-Selectin was expressed. These microparticles therefore constitute a promising SPECT imaging tool for AAA and potentially for other vascular diseases characterized by P-Selectin expression. Future work will focus on validating the efficiency of the microparticles to diagnose these other pathologies and the different stages of AAA. Incorporation of a therapeutic molecule is also considered.

Pulp cell tracking by radionuclide imaging for dental tissue engineering.

Pulp engineering with dental mesenchymal stem cells is a promising therapy for injured teeth. An important point is to determine the fate of implanted cells in the pulp over time and particularly during the early phase following implantation. Indeed, the potential engraftment of the implanted cells in other organs has to be assessed, in particular, to evaluate the risk of inducing ectopic mineralization. In this study, our aim was to follow by nuclear imaging the radiolabeled pulp cells after implantation in the rat emptied pulp chamber. For that purpose, indium-111-oxine (¹¹¹In-oxine)-labeled rat pulp cells were added to polymerizing type I collagen hydrogel to obtain a pulp equivalent. This scaffold was implanted in the emptied pulp chamber space in the upper first rat molar. Labeled cells were then tracked during 3 weeks by helical single-photon emission computed tomography (SPECT)/computed tomography performed on a dual modality dedicated small animal camera. Negative controls were performed using lysed radiolabeled cells obtained in a hypotonic solution. In vitro data indicated that ¹¹¹In-oxine labeling did not affect cell viability and proliferation. In vivo experiments allowed a noninvasive longitudinal follow-up of implanted living cells for at least 3 weeks and indicated that SPECT signal intensity was related to implanted cell integrity. Notably, there was no detectable systemic release of implanted cells from the tooth. In addition, histological analysis of the samples showed mitotically active fibroblastic cells as well as neoangiogenesis and nervous fibers in pulp equivalents seeded with entire cells, whereas pulp equivalents prepared from lysed cells were devoid of cell colonization. In conclusion, our study demonstrates that efficient labeling of pulp cells can be achieved and, for the first time, that these cells can be followed up after implantation in the tooth by nuclear imaging. Furthermore, it appears that grafted cells retained the label and are viable to follow the repair process. This technique is expected to be of major interest for monitoring implanted cells in innovative therapies for injured teeth.

Radiolabeled fucoidan as a p-selectin targeting agent for in vivo imaging of platelet-rich thrombus and endothelial activation.

UNLABELLED: P-selectin expression is involved in the pathophysiology of biologically active arterial thrombus and endothelial activation after a transient ischemic event. Fucoidan is a polysaccharidic ligand of P-selectin, with a nanomolar affinity. In the present study, we propose a new approach of P-selectin molecular imaging based on radiolabeled fucoidan. METHODS: Two kinds of experimental models were selected to evaluate the ability of radiolabeled fucoidan to detect P-selectin expression: platelet-rich arterial thrombi (vegetations of infective endocarditis and arterial mural thrombus) and myocardial ischemia-reperfusion. These 2 settings were chosen because they were clinically relevant, and both were associated with an important overexpression of platelet and endothelial P-selectin, respectively. RESULTS: (99m)Tc-fucoidan SPECT was able to detect the presence of platelet-rich arterial thrombi in all animals, with a median target-to-background ratio of 5.2 in vegetations of endocarditis and 3.6 in mural aneurysmal thrombus, and to detect a persistent endothelial activation at 2 h after reperfusion. In this latter model, the magnitude of the signal was correlated with the extent of myocardium that underwent transient ischemia. The sensitivity of selectivity of the uptake and retention of (99m)Tc-fucoidan in both settings was excellent. CONCLUSION: This study supports (99m)Tc-fucoidan as a relevant imaging agent for in vivo detection of biologic activities associated with P-selectin overexpression, such as arterial thrombus and ischemic memory. Given the reported wide availability at a low cost, and its low toxicity, fucoidan seems to overcome some of the limitations of previous P-selectin-targeted imaging agents.

[Kinetics of intracolloidal iodine within the thyroid of newborn rats. Direct imagery using secondary ion mass spectrometry]. / Cinétique intracolloïdale de l'iode dans la thyroïde de rat nouveau-né. Imagerie directe par microscopie ionique analytique.

The spatiotemporal distribution of cellular uptake site of radiotoxics is essential data for microdosimetric studies. As early as 1950, the heterogeneity of iodine incorporation within the thyroid has been shown using autoradiography. The objective of this study is to describe the kinetic cellular distribution of newly organified iodine in the thyroid of newborn rats using secondary ion mass microscopy (NanoSIMS50). Ionic images obtained at high mass resolution and with a lateral resolution of about 50 nm show that the early distribution of iodine is heterogeneous from one follicle to another, from one thyrocyte to another inside the same follicle, and that this distribution varies as a function of time. The obtained kinetic profile will allow us to refine the studies concerning the aetiopathology of thyroid cancers of the Chernobyl children.

Hormonal and psychological factors linked to the increased thermic effect of food in malnourished fasting anorexia nervosa.

OBJECTIVES: In patients with anorexia nervosa (AN), weight gain is lower than that expected from the energy content of the meals. Thus we investigated the thermic effect of food (TEF) in relation to subjective feelings and plasma hormone levels in a group of AN patients. METHODS: TEF, feelings (14 items), and plasma release of beta-endorphin, ACTH, cortisol, dopamine, and catecholamines were evaluated in 15 AN patients (body mass index, 13.6 +/- 1.2 kg.m(-2)) and in 15 healthy women after three gastric loads (0, 300, 700 kcal) infused by a nasogastric tube in a blind design. RESULTS: In AN, the blind loads induced an energy-dependent increase in TEF (P < 0.001), which was higher than that observed in healthy women (P < 0.001). Only in AN, a load-dependent decline in the high basal plasma level of beta-endorphin (P < 0.01), an increase in plasma ACTH (P < 0.02) after the two caloric loads, and an increase in cortisol, norepinephrine, and dopamine levels after the 700-kcal load only (P < 0.05) were noted. A calorie-dependent (P < 0.001) increase in nausea, abdominal discomfort, and fear of being fat ratings and a decrease in liking to eat (P < 0.001) and body image were observed in AN patients (P < 0.05). TEF correlated with ratings on satiation, nausea, uncomfortable abdominal swelling, body image, and fear of being fat (for all, P < 0.01). CONCLUSION: In AN women, blindly infused loads induced a dose-dependent increase in TEF, which correlated with the increase in plasma cortisol, ACTH, and catecholamines as in unpleasant sensations, fear of being fat, and anxiety as well as a decline in elevated basal beta-endorphin. These results could explain the difficulty for AN patients in gaining weight.

Induction of unstable and stable chromosomal aberrations by 99mTc: in-vitro and in-vivo studies.

BACKGROUND: Biological dosimetry, which determines the dose of acquired radiation by measuring radiation-induced variation of biological parameters, can help assess radiation damage in an individual. Evaluation of radiation exposure requires setting up reference curves for each type of radiation. AIM: To evaluate the potential induction of chromosome aberrations by a clinical diagnostic dose of 99mTc. METHODS: Dicentrics, rings, excess fragments, complete reciprocal translocations and incomplete reciprocal translocations were scored in peripheral blood lymphocytes from patients exposed to a 99mTc bone scintigraphy. A specific relationship between the radiation dose delivered by 99mTc and the frequency of stable and unstable chromosomal aberrations was established in vitro to estimate whole-body dose. Chromosome analysis using fluorescence plus Giemsa and fluorescence in-situ hybridization was undertaken on six patients before and after a 99mTc bone scintigraphy. Dicentrics, rings, excess fragments, and translocations were scored in blood lymphocytes after in vitro 99mTc external irradiation in order to construct dose calibration curves. RESULTS: Analysis of the in-vitro data shows that the number of both unstable and stable aberrations has a quadratic linear relationship to the dose. Our in-vivo irradiation studies showed that activities of 99mTc-hexamethylene diphosphonate (99mTc-HDP) used for bone investigations do not induce any additional unstable chromosome aberrations and translocations. The frequencies obtained did not differ significantly from background values. CONCLUSIONS: 99mTc can produce unstable and stable chromosomal aberrations in vitro. 99mTc-HDP administration does not induce supplementary chromosomal aberrations. The dose-response curves will allow a more accurate evaluation of the risk related to in-vivo administration of 99mTc labelled radiopharmaceuticals, and they can be used to assess the safe upper limit of injected activity in humans.

Aggression and the three opioid families (endorphins, enkephalins, and dynorphins) in mice.

Previous studies suggest that brain opioid activity decreases aggression in animal models. The main objective of the current study was to examine the possible genetic relationship between intermale aggression and brain levels of enkephalins, endorphins, and dynorphins in 11 inbred strains of mice. Pursuit, rattling, and attack behaviors were observed in a dyadic encounter with a standard opponent. It appeared that, as expected, enkephalins and endorphins were always negatively correlated with aggression scores. The findings indicate that brain Met5-enkephalin levels were significantly and highly positively correlated with attack latency. Brain adrenocorticotrophic hormone (ACTH) and beta-endorphin levels were significantly and negatively correlated with the number of rattlings, which is consistent with the hypothesis that rattling is a stress-related behavior. In contrast with Met5-enkephalin, ACTH and beta-endorphin, the correlations between dynorphin A and aggression scores were nonsignificant and very low. These preliminary results suggest that common genetic sources of variation contribute to differences between the 11 inbred strains in both endogenous opioidergic systems and intermale aggression. Further studies are required to confirm the genetic relationship between offensive aggression and brain enkephalins and endorphins and to better understand the mechanisms underlying the role of endogenous opioids in offensive aggression with regard to opioid receptor activity.

Distribution of injected MRI contrast agents in mouse livers studied by confocal and SIMS microscopy.

OBJECTIVE: To localize magnetic resonance imaging (MRI) contrast agents injected intravenously into mouse livers. STUDY DESIGN: Parallel studies were performed on fluorescent europium and nonfluorescent, paramagnetic gadolinium and on a product combining nanoparticles of Fe and Texas Red to obtain combined information on the distribution of these molecules inside the liver. The distribution of different superparamagnetic iron oxides was also studied because the size of these new compounds is not always convenientfor microcirculation studies. RESULTS: Europium and Texas Red can be detected by confocal microscopy. Europium, iron and gadolinium can be detected by secondary ion mass spectrometry (SIMS) microscopy. Studies confirmed the complementarity of both microscopies. They also confirmed the possibility of using europium as a model of gadolinium to analyze thefate of MRI contrast agents. CONCLUSION: The methodology can be used on mice injected intravenously and analyzed by confocal and SIMS microscopy to localize MRI contrast agents inside cellular and tissue specimens of mice.