Celine Baligand

Longitudinal measurements of MRI-T2 in boys with Duchenne muscular dystrophy: effects of age and disease progression.

Duchenne muscular dystrophy (DMD) is characterized by an increased muscle damage and progressive replacement of muscle by noncontractile tissue. Both of these pathological changes can lengthen the MRI transverse proton relaxation time (T2). The current study measured longitudinal changes in T2 and its distribution in the lower leg of 16 boys with DMD (5-13years, 15 ambulatory) and 15 healthy controls (5-13years). These muscles were chosen to allow extended longitudinal monitoring, due to their slow progression compared with proximal muscles in DMD. In the soleus muscle of boys with DMD, T2 and the percentage of pixels with an elevated T2 (⩾2SD above control mean T2) increased significantly over 1year and 2years, while the width of the T2 histogram increased over 2years. Changes in soleus T2 variables were significantly greater in 9-13years old compared with 5-8years old boys with DMD. Significant correlations between the change in all soleus T2 variables over 2years and the change in functional measures over 2years were found. MRI measurement of muscle T2 in boys with DMD is sensitive to disease progression and shows promise as a clinical outcome measure.

Chemical shift-based MRI to measure fat fractions in dystrophic skeletal muscle.

The relationship between fat fractions (FFs) determined based on multiple TE, unipolar gradient echo images and 1H magnetic resonance spectroscopy (MRS) was evaluated using different models for fat‐water decomposition, signal‐to‐noise ratios, and excitation flip angles.

Functional assessment of skeletal muscle in intact mice lacking myostatin by concurrent NMR imaging and spectroscopy

Inhibiting myostatin (mstn) causes spectacular increase in muscle mass, spurring research for therapeutic approaches against neuromuscular disorders. Yet, possible functional deterioration and compromised force production have been reported in isolated muscle of null mstn(−/−) mice. We analyzed vascular and metabolic response to repeated electro-stimulated exercise in vivo in mstn−/− mice compared with FVB wild-type controls (WT), using interleaved multi-parametric functional nuclear magnetic resonance (NMR) imaging and spectroscopy. At steady-state exercise, specific force of plantar flexion, phosphocreatine consumption measured by phosphorus spectroscopy and maximum perfusion measured by arterial spin-labeled (ASL) NMR imaging were identical in both groups. After exercise, phosphorus spectroscopy revealed reduced oxidative mitochondrial capacity in mstn−/−, whereas early recovery perfusion was identical and oxygen extraction, estimated from the blood oxygen level-dependent (BOLD) contrast, was decreased when compared with WT. Hyperemia was prolonged, indicating specific regulation of the perfusional response in mstn−/− mice. Histology showed an increased proportion of type IIb fibers in hypertrophied muscles, but the distribution of capillary contacts per fiber between oxidative and glycolytic fibers was unaltered in mstn−/− compared with WT. These integrated results formed coherent evidence of a congruous, non-pathologic shift toward a more glycolytic metabolism in this model of mstn−/−.

pH as a Biomarker of Neurodegeneration in Huntington's Disease: A Translational Rodent-Human MRS Study

Early diagnosis and follow-up of neurodegenerative diseases are often hampered by the lack of reliable biomarkers. Neuroimaging techniques like magnetic resonance spectroscopy (MRS) offer promising tools to detect biochemical alterations at early stages of degeneration. Intracellular pH, which can be measured noninvasively by 31P-MRS, has shown variations in several brain diseases. Our purpose has been to evaluate the potential of MRS-measured pH as a relevant biomarker of early degeneration in Huntingtons disease (HD). We used a translational approach starting with a preclinical validation of our hypothesis before adapting the method to HD patients. 31P-MRS-derived cerebral pH was first measured in rodents during chronic intoxication with 3-nitropropionic acid (3NP). A significant pH increase was observed early into the intoxication protocol (pH = 7.17 ± 0.02 after 3 days) as compared with preintoxication (pH = 7.08 ± 0.03). Furthermore, pH changes correlated with the 3NP-induced inhibition of succinate dehydrogenase and preceded striatum lesions. Using a similar MRS approach implemented on a clinical MRI, we then showed that cerebral pH was significantly higher in HD patients (n = 7) than in healthy controls (n = 6) (7.05 ± 0.03 versus 7.02 ± 0.01, respectively, P = 0.026). Altogether, both preclinical and human data strongly argue in favor of MRS-measured pH being a promising biomarker for diagnosis and follow-up of HD.

Investigating glycogenosis type III patients with multi-parametric functional NMR imaging and spectroscopy

Debranching enzyme deficiency (Glycogen storage disease (GSD) type III) causes progressive muscle wasting myopathy. A comprehensive nuclear magnetic resonance study involving spectroscopy (NMRS) and imaging (NMRI) evaluated status and function of calf muscles in 18 GSDIII patients. At rest, (31)P NMRS showed elevated pH and accumulation of anomalous phosphomonoesters, (13)C NMRS quantified excess glycogen accumulation and NMRI demonstrated progressive fat replacement that paralleled muscle weakness. Multi-parametric functional NMR, performed at recovery from a single bout of aerobic exercise, simultaneously assessed oxidative phosphorylation from (31)P NMRS, muscle perfusion and BOLD, a marker of blood oxygenation, from arterial spin labeled NMRI, and oxygen uptake from deoxymyoglobin proton NMRS. While blocked glycogenolysis caused inadequate substrate supply to the mitochondria, combined measurements suggested that altered perfusion was also responsible for impaired post-exercise phosphocreatine recovery and could contribute to exercise intolerance in GSDIII. These non-invasive investigations provide new indices to quantify the progression of GSDIII.

Discrepancies between the fate of myoblast xenograft in mouse leg muscle and NMR label persistency after loading with Gd-DTPA or SPIOs

1H-NMR (nuclear magnetic resonance) imaging is regularly proposed to non-invasively monitor cell therapy protocols. Prior to transplantation, cells must be loaded with an NMR contrast agent (CA). Most studies performed so far make use of superparamagnetic iron oxide particles (SPIOs), mainly for favorable detection sensitivity. However, in the case of labeled cell death, SPIO recapture by inflammatory cells might introduce severe bias. We investigated whether NMR signal changes induced by preloading with SPIOs or the low molecular weight gadolinium (Gd)-DTPA accurately monitored the outcome of transplanted cells in a murine model of acute immunologic rejection. CA-loaded human myoblasts were grafted in the tibialis anterior of C57BL/6 mice. NMR imaging was repeated regularly until 3 months post-transplantation. Label outcome was evaluated by the size of the labeled area and its relative contrast to surrounding tissue. In parallel, immunohistochemistry assessed the presence of human cells. Data analysis revealed that CA-induced signal changes did not strictly reflect the graft status. Gd-DTPA label disappeared rapidly yet with a 2-week delay compared with immunohistochemical evaluation. More problematically, SPIO label was still visible after 3 months, grossly overestimating cell survival (<1 week). SPIOs should be used with extreme caution to evaluate the presence of grafted cells in vivo and could hardly be recommended for the long-term monitoring of cell transplantation protocols.

Measuring perfusion and bioenergetics simultaneously in mouse skeletal muscle: a multiparametric functional-NMR approach

A totally noninvasive set‐up was developed for comprehensive NMR evaluation of mouse skeletal muscle function in vivo. Dynamic pulsed arterial spin labeling‐NMRI perfusion and blood oxygenation level‐dependent (BOLD) signal measurements were interleaved with 31P NMRS to measure both vascular response and oxidative capacities during stimulated exercise and subsequent recovery. Force output was recorded with a dedicated ergometer. Twelve exercise bouts were performed. The perfusion, BOLD signal, pH and force–time integral were obtained from mouse legs for each exercise. All reached a steady state after the second exercise, justifying the pointwise summation of the last 10 exercises to compensate for the limited 31P signal. In this way, a high temporal resolution of 2.5 s was achieved to provide a time constant for phosphocreatine (PCr) recovery (τPCr). The higher signal‐to‐noise ratio improved the precision of τPCr measurement [coefficient of variation (CV) = 16.5% vs CV = 49.2% for a single exercise at a resolution of 30 s]. Inter‐animal summation confirmed that τPCr was stable at steady state, but shorter (89.3 ± 8.6 s) than after the first exercise (148 s, p < 0.05). This novel experimental approach provides an assessment of muscle vascular response simultaneously to energetic function in vivo. Its pertinence was illustrated by observing the establishment of a metabolic steady state. This comprehensive tool offers new perspectives for the study of muscle pathology in mice models. Copyright

Fe doped CdTeS magnetic quantum dots for bioimaging

A facile synthesis of 3-6 nm, water dispersible, near-infrared (NIR) emitting, quantum dots (QDs) magnetically doped with Fe is presented. Doping of alloyed CdTeS nanocrystals with Fe was achieved in situ using a simple hydrothermal method. The magnetic quantum dots (MQDs) were capped with NAcetyl-Cysteine (NAC) ligands, containing thiol and carboxylic acid functional groups to provide stable aqueous dispersion. The optical and magnetic properties of the Fe doped MQDs were characterized using several techniques. The synthesized MQDs are tuned to emit in the Vis-NIR (530-738 nm) wavelength regime and have high quantum yields (67.5-10%). NIR emitting (738 nm) MQDs having 5.6 atomic% Fe content exhibited saturation magnetization of 85 emu/gm[Fe] at room temperature. Proton transverse relaxivity of the Fe doped MQDs (738 nm) at 4.7 T was determined to be 3.6 mM-1s-1. The functional evaluation of NIR MQDs has been demonstrated using phantom and in vitro studies. These water dispersible, NIR emitting and MR contrast producing Fe doped CdTeS MQDs, in unagglomerated form, have the potential to act as multimodal contrast agents for tracking live cells.

Non‐invasive and quantitative evaluation of peripheral vascular resistances in rats by combined NMR measurements of perfusion and blood pressure using ASL and dynamic angiography

The in vivo determination of peripheral vascular resistances (VR) is crucial for the assessment of arteriolar function. It requires simultaneous determination of organ perfusion (F) and arterial blood pressure (BP). A fully non‐invasive method was developed to measure systolic and diastolic BP in the caudal artery of rats based on dynamic NMR angiography. A good agreement was found between the NMR approach and the gold standard techniques (linear regression slope = 0.98, R2 = 0.96). This method and the ASL‐MRI measurement of skeletal muscle perfusion were combined into one single NMR experiment to quantitatively evaluate the local vascular resistances in the calf muscle of anaesthetized rats, in vivo and non‐invasively 1) at rest: VR = 7.0 ± 1.0 mmHg·min 100 g·ml−1, F = 13 ±  3 ml min−1.100 g−1 and mean BP (MBP) = 88 ± 10 mmHg; 2) under vasodilator challenge (milrinone): VR = 3.7 ± 1.1 mmHg min.100 g ml−1, F = 21 ± 4 ml min−1.100 g−1 and MBP = 75 ± 14 mmHg; 3) under vasopressor challenge (norepinephrine): VR = 9.8 ± 1.2 mmHg min 100 g ml−1, F = 14 ± 3 ml min−1.100 g−1 and MBP = 137 ± 2 mmHg. Copyright

Gene transfer of arginine kinase to skeletal muscle using adeno-associated virus.

In this study, we tested the feasibility of non-invasively measuring phosphoarginine (PArg) after gene delivery of arginine kinase (AK) using an adeno-associated virus (AAV) to murine hindlimbs. This was achieved by evaluating the time course, regional distribution and metabolic flux of PArg using 31phosphorus magnetic resonance spectroscopy (31P-MRS). AK gene was injected into the gastrocnemius of the left hindlimb of C57Bl10 mice (age 5 weeks, male) using self-complementary AAV, type 2/8 with desmin promoter. Non-localized 31P-MRS data were acquired over 9 months after injection using 11.1-T and 17.6-T Bruker Avance spectrometers. In addition, 31P two-dimensional chemical shift imaging and saturation transfer experiments were performed to examine the spatial distribution and metabolic flux of PArg, respectively. PArg was evident in each injected mouse hindlimb after gene delivery, increased until 28 weeks, and remained elevated for at least 9 months (P<0.05). Furthermore, PArg was primarily localized to the injected posterior hindimb region and the metabolite was in exchange with ATP. Overall, the results show the viability of AAV gene transfer of AK gene to skeletal muscle, and provide support of PArg as a reporter that can be used to non-invasively monitor the transduction of genes for therapeutic interventions.