[show abstract][hide abstract] ABSTRACT: PURPOSE: The purpose of this study was to introduce synchrotron radiation X-ray phase computed tomography (SR-PCT) as a new method of visualizing ultrasmall superparamagnetic particles of iron oxide (USPIO) distribution into the brains of mice with neuroinflammation. PROCEDURES: The sensitivity of the technique was assessed by performing back-to-back SR-PCT and magnetic resonance imaging (MRI) in mice stereotaxically injected with a range of USPIO concentrations. Eight mice with cerebral ischemia were then intravenously injected with USPIOs and imaged back-to-back with MRI and SR-PCT. RESULTS: SR-PCT proved sensitive enough to detect iron in nanomolar quantities. In stroke-induced animals, SR-PCT showed hyperintense areas in the regions of MR signal loss and immunostaining for macrophages. SR-PCT, moreover, identified brain anatomy as clearly as histology, without the need for sectioning or staining, with an examination time of 44 min per brain at an isotropic spatial resolution of 8 μm. CONCLUSION: SR-PCT has potential for cellular imaging in intact brain, with unequaled neuroanatomy.
Molecular imaging and biology: MIB: the official publication of the Academy of Molecular Imaging 04/2013; · 2.47 Impact Factor
[show abstract][hide abstract] ABSTRACT: THE INFLAMMATORY RESPONSE FOLLOWING ISCHEMIC STROKE IS DOMINATED BY INNATE IMMUNE CELLS: resident microglia and blood-derived macrophages. The ambivalent role of these cells in stroke outcome might be explained in part by the acquisition of distinct functional phenotypes: classically (M1) and alternatively activated (M2) macrophages. To shed light on the crosstalk between hypoxic neurons and macrophages, an in vitro model was set up in which bone marrow-derived macrophages were co-cultured with hippocampal slices subjected to oxygen and glucose deprivation. The results showed that macrophages provided potent protection against neuron cell loss through a paracrine mechanism, and that they expressed M2-type alternative polarization. These findings raised the possibility of using bone marrow-derived M2 macrophages in cellular therapy for stroke. Therefore, 2 million M2 macrophages (or vehicle) were intravenously administered during the subacute stage of ischemia (D4) in a model of transient middle cerebral artery occlusion. Functional neuroscores and magnetic resonance imaging endpoints (infarct volumes, blood-brain barrier integrity, phagocytic activity assessed by iron oxide uptake) were longitudinally monitored for 2 weeks. This cell-based treatment did not significantly improve any outcome measure compared with vehicle, suggesting that this strategy is not relevant to stroke therapy.
PLoS ONE 01/2013; 8(6):e67063. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: BACKGROUND: Irreversible damage may occur at reperfusion after sustained cerebral ischaemia. AIMS: We investigated the value of cyclosporine A for reducing the infarct size in a model of transient middle cerebral artery occlusion. METHODS: Twenty-seven Sprague-Dawley rats sustained a middle cerebral artery occlusion of one-hour. Acute multimodal Magnetic Resonance Imaging (MRI) was used during occlusion to confirm the success of surgery and measure baseline lesion size. Animals were randomly treated by: (i) intracarotid cyclosporine A (10 mg/kg) 20 mins before middle cerebral artery occlusion (pretreatment group); (ii) intracarotid cyclosporine A (10 mg/kg) immediately after reperfusion (post-treatment group); and (iii) intracarotid saline immediately after reperfusion. RESULTS: Histopathological measurements on day 1 showed a significant reduction of infarct size in the pretreatment group compared to the post-treatment (percentage values of ipsilateral hemispheres: 16 ± 5% vs. 29 ± 11%, P = 0·004) and saline groups (16 ± 5% vs. 42 ± 12%, P = 0·015). No significant difference was observed between the post-treatment and saline groups (P = 0·065). Behavioural examinations on day 1 showed no significant difference between groups. Immunohistochemistry showed a statistically significant reduction of microglial cell count in the pretreatment group compared to either saline or cyclosporine A post-treatment groups. CONCLUSIONS: We conclude that intracarotid cyclosporine A is effective in reducing infarct size when given prior to ischaemia, but not when administered at reperfusion.
International Journal of Stroke 08/2012; · 2.75 Impact Factor
[show abstract][hide abstract] ABSTRACT: OBJECTIVES: This study sought to evaluate whether the therapeutic effects of an anti-inflammatory drug such as minocycline could be monitored by serial ultrasmall superparamagnetic particles of iron oxide (USPIO)-enhanced MRI in experimental stroke. METHODS: Mice received a three-dose minocycline treatment (n = 12) or vehicle (n = 12) after permanent middle cerebral artery occlusion. USPIOs were administered 5 h post-surgery. MRI was performed before, 24 h and 48 h post-USPIO administration. MRI endpoints were the extent of signal abnormalities on R2 maps (=1/T2) and quantitative R2 changes over time (∆R2). Post-mortem brains were prepared either for immunohistology (n = 16) or for iron dosage (n = 8). RESULTS: As expected, treatment with minocycline significantly reduced infarct size, blood-brain barrier permeability and F4/80 immunostaining for microglia/macrophages. Areas of R2 maps > 35 ms(-1) also appeared significantly decreased in minocycline-treated mice (ANOVA for repeated measures, P = 0.017). There was a fair correlation between these areas and the amount of iron in the brain (R(2) = 0.69, P = 0.010), but no significant difference in ∆R2 was found between the two groups. CONCLUSIONS: This study showed that the extent of signal abnormalities on R2 maps can be used as a surrogate marker to detect minocycline effects in a murine experimental model of stroke. KEY POINTS : • Ultrasmall superparamagnetic particles of iron oxide offer new avenues for MRI research • Treatment of the inflammatory response following ischaemic stroke is currently undergoing evaluation. • Minocycline treatment significantly reduced areas of signal abnormalities on USPIO-enhanced MRI. • These areas correlated with the amount of iron in the brain. • Thus USPIO-enhanced MRI might provide a surrogate marker to monitor treatment.
[show abstract][hide abstract] ABSTRACT: Injection of thrombin into the middle cerebral artery (MCA) of mice has been proposed as a new model of thromboembolic stroke. The present study used sequential multiparametric Magnetic Resonance Imaging (MRI), including Magnetic Resonance Angiography (MRA), Diffusion-Weighted Imaging (DWI) and Perfusion-Weighted Imaging (PWI), to document MCA occlusion, PWI-DWI mismatch, and lesion development. In the first experiment, complete MCA occlusion and reproducible hypoperfusion were obtained in 85% of animals during the first hour after stroke onset. In the second experiment, 80% of animals showed partial to complete reperfusion during a three-hour follow-up. Spontaneous reperfusion thus contributed to the variability in ischemic volume in this model. The study confirmed the value of the model for evaluating new thrombolytic treatments, but calls for extended MRI follow-up at the acute stage in therapeutic studies.
PLoS ONE 01/2012; 7(11):e50083. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Models of intraluminal middle cerebral artery occlusion present an intrinsic variability in infarct size. Behavioral evaluation is frequently performed during arterial occlusion to confirm success of surgery. AIMS AND/OR HYPOTHESIS: We compared the value of behavioral testing and multimodal magnetic resonance imaging performed during arterial occlusion for identifying successfully operated animals.
Rats were tested with behavioral assessment (using three scoring scales and the adhesive removal test) and multimodal magnetic resonance imaging (including magnetic resonance angiography, diffusion-weighted and perfusion-weighted imaging), both performed during the two-hours of middle cerebral artery occlusion using the intraluminal suture model. Behavioral assessment was repeated 24 h after reperfusion, followed by sacrifice.
Acute apparent diffusion coefficient lesion volume was correlated with both 2,3,5-triphenyl tetrazolium chloride infarct size (r = 0·75, P = 0·02) and behavioral status (r = 0·66, P = 0·05) on day one. Conversely, no correlation was found between acute behavioral examination and day one outcomes (2,3,5-triphenyl tetrazolium chloride infarct volume, r = 0·40, P = 0·28; behavioral examination, r = 0·39, P = 0·30). Day zero apparent diffusion coefficient volumes (P = 0·04), but not behavioral assessment (P = 0·60), discriminated animals with day one corticostriatal infarcts from these with subcortical infarcts.
Acute behavioral testing performed during arterial occlusion fails to identify successfully operated animals. Acute diffusion magnetic resonance imaging may be more appropriate to assess and reduce infarct size variability in this model.
International Journal of Stroke 12/2011; 7(6):465-72. · 2.75 Impact Factor
[show abstract][hide abstract] ABSTRACT: To quantify small amounts of iron-labeled cells in mouse brains with magnetic resonance imaging (MRI).
Iron-labeled cells (from 500 to 7,500) were stereotaxically transplanted into the brain of living mice that were subsequently imaged with MRI at 4.7 T. We compared four quantitative methods: (1) T2 relaxometry, (2) T2* relaxometry, (3) the volume of the cloverleaf hypointense artifact generated on T2*-weighted images, and (4) the volume of the cloverleaf hyperintense artifact generated on positive contrast images.
The methods based on relaxometry, whether T2 or T2*, did not correlate with the number of injected cells. By contrast, those based on measurement of cloverleaf artifact volume, whether using negative or positive enhancement, showed a significant linear relationship for the given range of cells (R [0.92-0.95], p < 0.05).
T2* artifact volume imaging (negative or positive) appears promising for the quantification of magnetically labeled cells following focal injection in the brain.
Molecular imaging and biology: MIB: the official publication of the Academy of Molecular Imaging 08/2011; 13(4):672-8. · 2.47 Impact Factor
[show abstract][hide abstract] ABSTRACT: Epidemiologic studies report cardiovascular protection conferred by omega-3 fatty acids, in particular docosahexaenoic acid (DHA). However, few experimental studies have addressed its potential in acute stroke treatment. The present study used multimodal MRI to assess in vivo the neuroprotection conferred by DHA and by a brain-targeting form of DHA-containing lysophosphatidylcholine (AceDoPC) in experimental stroke. Rats underwent intraluminal middle cerebral artery occlusion (MCAO) and were treated at reperfusion by intravenous injection of i) saline, ii) plasma from donor rats, iii) DHA or iv) AceDoPC, both solubilized in plasma. Twenty-four hours after reperfusion, animals underwent behavioral tests and were sacrificed. Multiparametric MRI (MRA, DWI, PWI, T2-WI) was performed at H0, during occlusion, and at H24, before sacrifice. Brain tissue was used for assay of F2-isoprostanes as lipid peroxidation markers. Initial lesion size and PWI/DWI mismatch were comparable in the four groups. Between H0 and H24, lesion size increased in the saline group (mean±s.d.: +18%±20%), was stable in the plasma group (-3%±29%), and decreased in the DHA (-17%±15%, P=0.001 compared to saline) and AceDoPC (-34%±27%, P=0.001 compared to saline) groups. Neuroscores in the AceDoPC group tended to be lower than in the other groups (P=0.07). Treatments (pooled DHA and AceDoPC groups) significantly decreased lipid peroxidation as compared to controls (pooled saline and vehicle) (P=0.03). MRI-based assessment demonstrated the neuroprotective effect of DHA in the MCAO model. Results further highlighted the therapeutic potential of engineered brain-targeting forms of omega-3 fatty acids for acute stroke treatment.
Current Neurovascular Research 04/2011; 8(2):95-102. · 2.84 Impact Factor
[show abstract][hide abstract] ABSTRACT: Epidemiologic studies report cardiovascular protection conferred by omega-3 fatty acids, in particular docosahexaenoic acid (DHA). However, few experimental studies have addressed its potential in acute stroke treatment. The present study used multimodal MRI to assess in vivo the neuroprotection conferred by DHA and by a brain-targeting form of DHA-containing lysophosphatidylcholine (AceDoPC) in experimental stroke. Rats underwent intraluminal middle cerebral artery occlusion (MCAO) and were treated at reperfusion by intravenous injection of i) saline, ii) plasma from donor rats, iii) DHA or iv) AceDoPC, both solubilized in plasma. Twenty-four hours after reperfusion, animals underwent behavioral tests and were sacrificed. Multiparametric MRI (MRA, DWI, PWI, T2-WI) was performed at H0, during occlusion, and at H24, before sacrifice. Brain tissue was used for assay of F(2)-isoprostanes as lipid peroxidation markers. Initial lesion size and PWI/DWI mismatch were comparable in the four groups. Between H0 and H24, lesion size increased in the saline group (mean ± s.d.: +18% ± 20%), was stable in the plasma group (-3% ± 29%), and decreased in the DHA (-17% ± 15%, P=0.001 compared to saline) and AceDoPC (-34% ± 27%, P=0.001 compared to saline) groups. Neuroscores in the AceDoPC group tended to be lower than in the other groups (P=0.07). Treatments (pooled DHA and AceDoPC groups) significantly decreased lipid peroxidation as compared to controls (pooled saline and vehicle) (P=0.03). MRI-based assessment demonstrated the neuroprotective effect of DHA in the MCAO model. Results further highlighted the therapeutic potential of engineered brain-targeting forms of omega-3 fatty acids for acute stroke treatment.
Current neurovascular research 03/2011; 8(2):95-102. · 3.23 Impact Factor
[show abstract][hide abstract] ABSTRACT: Objectives
To monitor by magnetic resonance imaging (MRI) intra-carotid injection of labeled macrophages in an animal model of stroke, and to characterize the cellular biotransformation of iron nanoparticles using transmission electron microscopy (TEM).
[show abstract][hide abstract] ABSTRACT: Stroke is the third leading cause of death, after myocardial infarction and cancer, and the leading cause of permanent disability in Western countries. Although anti-inflammatory drugs have shown very promising results in preclinical rodent studies, they appeared to be ineffective against stroke in clinical trials. In this context, non-invasive detection of inflammatory cells after brain ischemia could be helpful (i) to select patients who may benefit from anti-inflammatory treatment, and/or (ii) to target an adequate individualized therapeutic time window. Magnetic resonance imaging (MRI) coupled with injection of iron oxide nanoparticles, a contrast agent taken up by macrophages ex vivo and in vivo, appears to be a promising tool for this purpose. This review focuses on the use of this technique to image inflammation in pre-clinical and clinical studies of stroke. Despite current limitations, MRI of inflammation may become an important tool for the investigation of novel ischemic stroke therapeutics targeting inflammation.
International journal of clinical pharmacology and therapeutics 11/2010; 48(11):718-28. · 1.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: Neuroinflammation is involved in neurological disorders through the activation of microglial cells. Imaging of neuroinflammation with radioligands for the translocator protein (18 kDa) (TSPO) could prove to be an attractive biomarker for disease diagnosis and therapeutic evaluation. The indoleacetamide-derived 7-chloro-N,N,5-trimethyl-4-oxo-3-phenyl-3,5-dihydro-4H-pyridazino[4,5-b]indole-1-acetamide, SSR180575, is a selective high-affinity TSPO ligand in human and rodents with neuroprotective effects.
Here we report the radiolabelling of SSR180575 with (11)C and in vitro and in vivo imaging in an acute model of neuroinflammation in rats.
The image contrast and the binding of [(11)C]SSR180575 are higher than that obtained with the isoquinoline-based TSPO radioligand, [(11)C]PK11195. Competition studies demonstrate that [(11)C]SSR180575 has high specific binding for the TSPO.
[(11)C]SSR180575 is the first PET radioligand for the TSPO based on an indoleacetamide scaffold designed for imaging neuroinflammation in animal models and in the clinic.
European Journal of Nuclear Medicine 10/2010; 38(3):509-14. · 4.53 Impact Factor
[show abstract][hide abstract] ABSTRACT: The key role of neuroinflammation in acute and chronic neurological disorders has stimulated the search for specific radiotracers targeting the peripheral benzodiazepine receptor (PBR)/18 kDa translocator protein (TSPO), a hallmark of neuroinflammation. Here we evaluate the new radiotracer for positron emission tomography (PET) [(18)F]PBR111 in a rodent model of acute inflammation and compare it with [(11)C]CLINME, an (11)C-labelled tracer of the same chemical family, and with the isoquinolinic carboxamide [(11)C]PK11195.
We studied radiometabolites by HPLC, in vitro binding by autoradiography and in vivo brain kinetics as well as in vivo specificity of binding using PET imaging.
We show that this radiotracer has a high in vitro specificity for PBR/TSPO versus central benzodiazepine receptors, as reflected by the drastic reduction of its binding to target tissue by addition of PK11195 or PBR111, while addition of flumazenil does not affect binding. Only intact [(18)F]PBR111 is detected in brain up to 60 min after i.v. injection, and PET imaging shows an increased uptake in the lesion as compared to the contralateral side as early as 6 min after injection. Administration of an excess of PK11195 and PBR111, 20 min after [(18)F]PBR111 administration, induces a rapid and complete displacement of [(18)F]PBR111 binding from the lesion. Modelling of the PET data using the simplified reference tissue model showed increased binding potential (BP) in comparison to [(11)C]PK11195.
[(18)F]PBR111 is a metabolically stable tracer with a high specific in vitro and in vivo binding to TSPO. In addition, considering the longer half-life of (18)F over (11)C, these results support [(18)F]PBR111 as a promising PET tracer of the PBR/TSPO for neuroinflammation imaging.
European Journal of Nuclear Medicine 05/2010; 37(5):962-72. · 4.53 Impact Factor
[show abstract][hide abstract] ABSTRACT: Permanent middle cerebral artery (MCA) occlusion (pMCAO) by electrocoagulation is a commonly used model but with potential traumatic lesions. Early MRI monitoring may assess pMCAO for non-specific brain damage. The surgical steps of pMCAO were evaluated for traumatic cerebral injury in 22 Swiss mice using diffusion and T2-weighted MRI (7T) performed within 1 h and 24 h after surgery. Temporal muscle cauterization without MCA occlusion produced an early T2 hyperintensity mimicking an infarct. No lesion was visible after temporal muscle incision or craniotomy. Early MRI monitoring is useful to identify non-specific brain injury that could hamper neuroprotective drugs assessment.
Experimental and Translational Stroke Medicine 01/2010; 2(1):4.
[show abstract][hide abstract] ABSTRACT: MRI coupled with the intravenous injection of ultrasmall superparamagnetic particles of iron oxides (USPIOs) is a promising tool for the study of neuroinflammation. Quantification of the approximate number of magnetically labelled macrophages may provide an effective and efficient method for monitoring inflammatory cells. The purpose of the present study was to characterise the relaxation properties of macrophages labelled with two types of USPIOs, at 4.7 T and 7 T.
USPIO-labelled bone-marrow-derived macrophage phantoms were compared with phantoms of free dispersed USPIOs with the same global iron concentration, using multi-parametric (T1, T2 and T2) quantitative MRI. The same protocol was then evaluated in living mice after intracerebral injection of iron-labelled macrophages vs free iron oxide.
A linear relationship was observed among R1, R2 and R2 values and iron concentration in vitro at 4.7 T and at 7 T. At a given field, T1 and T2 relaxivities of both types of USPIOs decreased following internalisation into macrophages, while T2 relaxivities increased.
There was fair overall agreement between the theoretical number of injected cells and the number estimated from T2 quantification and in vitro calibration curves, supporting the validity of the present in vitro calibration curves for in vivo investigation.
European Radiology 09/2009; 20(2):275-85. · 3.55 Impact Factor
[show abstract][hide abstract] ABSTRACT: Overexpression of the translocator protein, TSPO (18 kDa), formerly known as the peripheral benzodiazepine receptor, is a hallmark of activation of cells of monocytic lineage (microglia and macrophages) during neuroinflammation. Radiolabeling of TSPO ligands enables the detection of neuroinflammatory lesions by PET. Two new radioligands, (11)C-labeled N,N-diethyl-2-[2-(4-methoxyphenyl)-5,7-dimethylpyrazolo[1,5-alpha]pyrimidin-3-yl]acetamide (DPA-713) and (18)F-labeled N,N-diethyl-2-(2-(4-(2-fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-alpha]pyrimidin-3-yl)acetamide (DPA-714), both belonging to the pyrazolopyrimidine class, were compared in vivo and in vitro using a rodent model of neuroinflammation.
(11)C-DPA-713 and (18)F-DPA-714, as well as the classic radioligand (11)C-labeled (R)-N-methyl-N-(1-methylpropyl)-1-(2-chlorophenyl)isoquinoline-3-carboxamide (PK11195), were used in the same rat model, in which intrastriatal injection of (R,S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolopropionique gave rise to a strong neuroinflammatory response. Comparative endpoints included in vitro autoradiography and in vivo imaging on a dedicated small-animal PET scanner under identical conditions.
(11)C-DPA-713 and (18)F-DPA-714 could specifically localize the neuroinflammatory site with a similar signal-to-noise ratio in vitro. In vivo, (18)F-DPA-714 performed better than (11)C-DPA-713 and (11)C-PK11195, with the highest ratio of ipsilateral to contralateral uptake and the highest binding potential.
(18)F-DPA-714 appears to be an attractive alternative to (11)C-PK11195 because of its increased bioavailability in brain tissue and its reduced nonspecific binding. Moreover, its labeling with (18)F, the preferred PET isotope for radiopharmaceutical chemistry, favors its dissemination and wide clinical use. (18)F-DPA-714 will be further evaluated in longitudinal studies of neuroinflammatory conditions such as are encountered in stroke or neurodegenerative diseases.
Journal of Nuclear Medicine 03/2009; 50(3):468-76. · 5.77 Impact Factor