Bich-Thuy Doan

Detection of Enzymatic Activity by PARACEST MRI: A General Approach to Target a Large Variety of Enzymes

We report a new family of molecular imaging probes that offer the possibility of specific PARACEST (paramagnetic chemical exchange saturation transfer) MRI detection of a large variety of enzymatic activities. The probes are based on a lanthanide complex coupled to an enzyme-specific substrate through a self-immolative spacer. Upon enzymatic cleavage of the substrate, the spacer is spontaneously eliminated, thereby resulting in a remarkable change in the PARACEST properties of the Ln3+ chelate. This new type of contrast agent opens up new perspectives in molecular magnetic resonance imaging.

In vivo cellular imaging of lymphocyte trafficking by MRI: a tumor model approach to cell-based anticancer therapy.

The aim of this study was to demonstrate the feasibility of in vivo cell tracking to monitor anticancer cell therapy by means of a high‐resolution noninvasive MRI method. Ovalbumin‐specific splenocytes (OT‐1) labeled with anionic γ‐Fe2O3 superparamagnetic iron oxide (SPIO) nanoparticles were adoptively transferred into C57BL/6 mice with growing ovalbumin‐expressing tumors. OT‐1 cells were tracked in vivo by 7 T MRI 24, 48, and 72 hr after they were injected. The results showed significant negative enhancement of the spleen at 24 hr, and of the tumor at 48 and 72 hr, after labeled cell injection. This suggests that the lymphocytes initially homed toward the spleen and were then recruited by the tumor. The presence of labeled cells was confirmed in ex vivo by 9.4 T microimaging of tumors and magnetic sorting of spleen cells. These results confirm that MR tracking of lymphocytes is feasible in vivo. This high‐resolution imaging method could be used to improve the monitoring of immune cell therapy. Magn Reson Med, 2006.

Both Functional LTβ Receptor and TNF Receptor 2 Are Required for the Development of Experimental Cerebral Malaria

Background TNF-related lymphotoxin α (LTα) is essential for the development of Plasmodium berghei ANKA (PbA)-induced experimental cerebral malaria (ECM). The pathway involved has been attributed to TNFR2. Here we show a second arm of LTα-signaling essential for ECM development through LTβ-R, receptor of LTα1β2 heterotrimer. Methodology/Principal Findings LTβR deficient mice did not develop the neurological signs seen in PbA induced ECM but died at three weeks with high parasitaemia and severe anemia like LTαβ deficient mice. Resistance of LTαβ or LTβR deficient mice correlated with unaltered cerebral microcirculation and absence of ischemia, as documented by magnetic resonance imaging and angiography, associated with lack of microvascular obstruction, while wild-type mice developed distinct microvascular pathology. Recruitment and activation of perforin+ CD8+ T cells, and their ICAM-1 expression were clearly attenuated in the brain of resistant mice. An essential contribution of LIGHT, another LTβR ligand, could be excluded, as LIGHT deficient mice rapidly succumbed to ECM. Conclusions/Significance LTβR expressed on radioresistant resident stromal, probably endothelial cells, rather than hematopoietic cells, are essential for the development of ECM, as assessed by hematopoietic reconstitution experiment. Therefore, the data suggest that both functional LTβR and TNFR2 signaling are required and non-redundant for the development of microvascular pathology resulting in fatal ECM.

Chronic exposure to glufosinate-ammonium induces spatial memory impairments, hippocampal MRI modifications and glutamine synthetase activation in mice.

Glufosinate-ammonium (GLA), the active compound of a worldwide-used herbicide, acts by inhibiting the plant glutamine synthetase (GS) leading to a lethal accumulation of ammonia. GS plays a pivotal role in the mammalian brain where it allows neurotransmitter glutamate recycling within astroglia. Clinical studies report that an acute GLA ingestion induces convulsions and memory impairment in humans. Toxicological studies performed at doses used for herbicidal activity showed that GLA is probably harmless at short or medium range periods. However, effects of low doses of GLA on chronically exposed subjects are not known. In our study, C57BL/6J mice were treated during 10 weeks three times a week with 2.5, 5 and 10mg/kg of GLA. Effects of this chronic treatment were assessed at behavioral, structural and metabolic levels by using tests of spatial memory, locomotor activity and anxiety, hippocampal magnetic resonance imaging (MRI) texture analysis, and hippocampal GS activity assay, respectively. Chronic GLA treatments have effects neither on anxiety nor on locomotor activity of mice but at 5 and 10mg/kg induce (1) mild memory impairments, (2) a modification of hippocampal texture and (3) a significant increase in hippocampal GS activity. It is suggested that these modifications may be causally linked one to another. Since glutamate is the main neurotransmitter in hippocampus where it plays a crucial role in spatial memory, hippocampal MRI texture and spatial memory alterations might be the consequences of hippocampal glutamate homeostasis modification revealed by increased GS activity in hippocampus. The present study provides the first data that show cerebral alterations after chronic exposure to GLA.

Functionalized single-walled carbon nanotubes containing traces of iron as new negative MRI contrast agents for in vivo imaging

Single-walled carbon nanotubes (SWCNTs) containing traces of iron oxide were functionalized by noncovalent lipid-PEG or covalent carboxylic acid function to supply new efficient MRI contrast agents for in vitro and in vivo applications. Longitudinal (r(1)) and transversal (r(2)) water proton relaxivities were measured at 300 MHz, showing a stronger T(2) feature as an MRI contrast agent (r(2)/r(1)  = 190 for CO(2) H functionalisation). The r(2) relaxivity was demonstrated to be correlated to the presence of iron oxide in the SWNT-carboxylic function COOH, in comparison to iron-free ones. Biodistribution studies on mice after a systemic injection showed a negative MRI contrast in liver, suggesting the presence of the nanotubes in this organ until 48 h after i.v. injection. The presence of carbon nanotubes in liver was confirmed after ex vivo carbon extraction. Finally, cytotoxicity studies showed no apparent effect owing to the presence of the carbon nanotubes. The functionalized carbon nanotubes were well tolerated by the animals at the dose of 10 µg g(-1) body weight.

Magnetic resonance imaging of Klebsiella pneumoniae-induced pneumonia in mice.

In vivo imaging of small animals is a rapidly developing field. However, the potential of global imaging of infectious processes in animal models remains poorly explored. We used magnetic resonance imaging (MRI) to follow the development and regression of inflammatory lesions caused by infection by Klebsiella pneumoniae in mouse lungs. A virulent strain caused an intense inflammation within 2 days in the whole lungs, while an avirulent strain did not show significant changes. Mice infected with the virulent strain and subsequently treated with antibiotics presented a severe inflammation localized mainly in the left lung that disappeared after a week. The lesions observed by MRI correlated with the damage seen by histological analysis and a 3D representation of the tissue allowed better visualization of the development and healing of inflammatory lesions. MRI thus represents a powerful technique to study in vivo the interactions between a pathogen and its host in real time.

KIT is required for hepatic function during mouse post-natal development

BackgroundThe Kit gene encodes a receptor tyrosine kinase involved in various biological processes including melanogenesis, hematopoiesis and gametogenesis in mice and human. A large number of Kit mutants has been described so far showing the pleiotropic phenotypes associated with partial loss-of-function of the gene. Hypomorphic mutations can induce a light coat color phenotype while complete lack of KIT function interferes with embryogenesis. Interestingly several intermediate hypomorphic mutations induced in addition growth retardation and post-natal mortality.ResultsIn this report we investigated the post-natal role of Kit by using a panel of chemically-induced hypomorphic mutations recently isolated in the mouse. We found that, in addition to the classical phenotypes, mutations of Kit induced juvenile steatosis, associated with the downregulation of the three genes, VldlR, Lpin1 and Lpl, controlling lipid metabolism in the post-natal liver. Hence, Kit loss-of-functions mimicked the inactivation of genes controlling the hepatic metabolism of triglycerides, the major source of energy from maternal milk, leading to growth and viability defects during neonatal development.ConclusionThis is a first report involving KIT in the control of lipid metabolism in neonates and opening new perspectives for understanding juvenile steatosis. Moreover, it reinforces the role of Kit during development of the liver and underscores the caution that should be exerted in using KIT inhibitors during anti-cancer treatment.

In vivo 2D magnetic resonance spectroscopy of small animals

Localized in vivo NMR spectroscopy, chemical shift imaging or multi-voxel spectroscopy are potentially useful tools in small animals that are complementary to MRI, adding biochemical information to the mainly anatomical data provided by imaging of water protons. However the contribution of such methods remains hampered by the low spectral resolution of the in vivo 1D spectra. Two-dimensional methods widely developed for in vitro studies have been proposed as suitable approaches to overcome these limitations in resolution. The different homonuclear and heteronuclear sequences adapted to in vivo studies are reviewed. Their specific contributions to the spectral resolution of spectroscopic data and their limitations for in vivo investigations are discussed. The applications to experimental models of pathological processes or pharmacological treatment in mainly brain and muscle are presented. According to their combined sensitivity, acquisition duration and spatial resolution, the heteronuclear 2D experiments, which are mainly used for 1H detected-13C spectroscopy after administration of 13C-labeled compounds, appear to be less efficient than 1H detected-13C 1D methods at high field. However, the applications of 2D proton homonuclear methods show that they remain the best tools for in vivo studies when an improved resolution is required.

Analysis of polyaromatics in crude gas oil mixtures: a new strategy using 1H 2D n.m.r.

A new method for analysing complex mixtures, 1H 2D n.m.r., was used to determine polyaromatics in crude gas oil mixtures. 2D NMR overcomes the lack of resolution due to crowded 1D spectra and provides structural information. In particular, TOCSY (total correlation spectroscopy) 2D n.m.r. is well suited to polyaromatics because these molecules give specific 2D fingerprints which can be easily recognized. These patterns were selected and analysed in two ways: (1) specific fingerprint recognition using a pure compound library; (2) using the mixing time τm of the TOCSY sequence. Variation of τm gives a change in cross-peak intensities. The intensity variation curves are characteristic of spin systems and hence of the structures of compounds. Alkylated substitutions were also studied. The compounds were quantified. This strategy was used to analyse crude gas oils and measure the contents of separated alkylated naphthalene isomers, biphenyls, anthracene, phenanthrene and benzothiophene.

Evaluation of Nonradiative Clinical Imaging Techniques for the Longitudinal Assessment of Tumour Growth in Murine CT26 Colon Carcinoma

Background and Objectives. To determine the most appropriate technique for tumour followup in experimental therapeutics, we compared ultrasound (US) and magnetic resonance imaging (MRI) to characterize ectopic and orthotopic colon carcinoma models. Methods. CT26 tumours were implanted subcutaneously (s.c.) in Balb/c mice for the ectopic model or into the caecum for the orthotopic model. Tumours were evaluated by histology, spectrofluorescence, MRI, and US. Results. Histology of CT26 tumour showed homogeneously dispersed cancer cells and blood vessels. The visualization of the vascular network using labelled albumin showed that CT26 tumours were highly vascularized and disorganized. MRI allowed high-resolution and accurate 3D tumour measurements and provided additional anatomical and functional information. Noninvasive US imaging allowed good delineation of tumours despite an hypoechogenic signal. Monitoring of tumour growth with US could be accomplished as early as 5 days after implantation with a shorter acquisition time (<5 min) compared to MRI. Conclusion. MRI and US afforded excellent noninvasive imaging techniques to accurately follow tumour growth of ectopic and orthotopic CT26 tumours. These two techniques can be appropriately used for tumour treatment followup, with a preference for US imaging, due to its short acquisition time and simplicity of use.