Non-invasive tracking of disease progression in young dystrophic muscles using multi-parametric MRI at 14T.

In this study, multi-parametric magnetic resonance imaging (MRI) was conducted to monitor skeletal muscle changes in dystrophic (mdx4cv) and age-matched control (C57BL/6J) mice starting at 3 weeks of age. The objective of this study was to evaluate and characterize changes in muscle tissue characteristics of hind limbs in young, dystrophic mice using MRI. Mdx4cv (n = 25) and age-matched C57BL/6J (n = 5) were imaged at 3, 5, 7, 9, and 11 weeks of age. Multiple MR measurements were taken from the tibialis anterior, gastrocnemius, and soleus muscles. There were significant differences between dystrophic and control groups for all three muscle types when comparing transverse relaxation times (T2) in lower hind limb muscles. Additionally, fractional anisotropy, radial diffusivity, and eigenvalue analysis of diffusion tensor imaging also demonstrated significant differences between groups. Longitudinal relaxation times (T1) displayed no significant differences between groups. The earliest time points in the magnetization transfer ratio measurements displayed a significant difference. Histological analysis revealed significant differences in the tibialis anterior and gastrocnemius muscles between groups with the mdx mice displaying greater variability in muscle fiber size in later time points. The multi-parametric MRI approach offers a promising alternative for future development of a noninvasive avenue for tracking both disease progression and treatment response

13C/31P MRS Metabolic Biomarkers of Disease Progression and Response to AAV Delivery of hGAA in a Mouse Model of Pompe Disease

The development of therapeutic clinical trials for glycogen storage disorders, including Pompe disease, has called for non-invasive and objective biomarkers. Glycogen accumulation can be measured in vivo with 13C MRS. However, clinical implementation remains challenging due to low signal-to-noise. On the other hand, the buildup of glycolytic intermediates may be detected with 31P MRS. We sought to identify new biomarkers of disease progression in muscle using 13C/31P MRS and 1H HR-MAS in a mouse model of Pompe disease (Gaa−/−). We evaluated the sensitivity of these MR biomarkers in vivo after treatment using an adeno-associated virus vector 2/9 encoding hGAA driven by the desmin promotor. 31P MRS showed significantly elevated phosphomonoesters (PMEs) in Gaa−/− compared to control at 2 (0.06 ± 0.02 versus 0.03 ± 0.01; p = 0.003), 6, 12, and 18 months of age. Correlative 1H HR-MAS measures in intact gastrocnemius muscles revealed high glucose-6-phosphate (G-6-P). After intramuscular AAV injections, glycogen, PME, and G-6-P were decreased within normal range. The changes in PME levels likely partly resulted from changes in G-6-P, one of the overlapping phosphomonoesters in the 31P MR spectra in vivo. Because 31P MRS is inherently more sensitive than 13C MRS, PME levels have greater potential as a clinical biomarker and should be considered as a complementary approach for future studies in Pompe patients

Magnetic Resonance Assessment of Hypertrophic and Pseudo-Hypertrophic Changes in Lower Leg Muscles of Boys with Duchenne Muscular Dystrophy and Their Relationship to Functional Measurements.

The primary objectives of this study were to evaluate contractile and non-contractile content of lower leg muscles of boys with Duchenne muscular dystrophy (DMD) and determine the relationships between non-contractile content and functional abilities.Lower leg muscles of thirty-two boys with DMD and sixteen age matched unaffected controls were imaged. Non-contractile content, contractile cross sectional area and non-contractile cross sectional area of lower leg muscles (tibialis anterior, extensor digitorum longus, peroneal, medial gastrocnemius and soleus) were assessed by magnetic resonance imaging (MRI). Muscle strength, timed functional tests and the Brooke lower extremity score were also assessed.Non-contractile content of lower leg muscles (peroneal, medial gastrocnemius, and soleus) was significantly greater than control group (p<0.05). Non-contractile content of lower leg muscles correlated with Brooke score (rs = 0.64-0.84) and 30 feet walk (rs = 0.66-0.80). Dorsiflexor (DF) and plantarflexor (PF) specific torque was significantly different between the groups.Overall, non-contractile content of the lower leg muscles was greater in DMD than controls. Furthermore, there was an age dependent increase in contractile content in the medial gastrocnemius of boys with DMD. The findings of this study suggest that T1 weighted MR images can be used to monitor disease progression and provide a quantitative estimate of contractile and non-contractile content of tissue in children with DMD

Contrast-Enhanced Near-Infrared Optical Imaging Detects Exacerbation and Amelioration of Murine Muscular Dystrophy

Assessment of muscle pathology is a key outcome measure to measure the success of clinical trials studying muscular dystrophies; however, few robust minimally invasive measures exist. Indocyanine green (ICG)-enhanced near-infrared (NIR) optical imaging offers an objective, minimally invasive, and longitudinal modality that can quantify pathology within muscle by imaging uptake of ICG into the damaged muscles. Dystrophic mice lacking dystrophin (mdx) or gamma-sarcoglycan (Sgcg −/− ) were compared to control mice by NIR optical imaging and magnetic resonance imaging (MRI). We determined that optical imaging could be used to differentiate control and dystrophic mice, visualize eccentric muscle induced by downhill treadmill running, and restore the membrane integrity in Sgcg −/− mice following adeno-associated virus (AAV) delivery of recombinant human SGCG (desAAV8hSGCG). We conclude that NIR optical imaging is comparable to MRI and can be used to detect muscle damage in dystrophic muscle as compared to unaffected controls, monitor worsening of muscle pathology in muscular dystrophy, and assess regression of pathology following therapeutic intervention in muscular dystrophies

Relationship between NCC of different leg muscles and 30 feet walk (sec).

<p>There was a significant relationship between increase in NCC of all leg muscles and time taken to cover 30 feet distance (r_s; 0.65–0.80, p<0.0001).</p

Contractile cross sectional area (C-CSA), non-contractile cross sectional area (NC-CSA), and non-contractile content (NCC) of all the lower leg muscles of boys with DMD and healthy control subjects.

<p>Significant difference was found in NC-CSA and of peroneal (Per), medial gastrocnemius (MG), and soleus (SOL) (denoted by **, p<0.05). No differences were observed in C-CSA of DMD and Ctrl leg muscles when all age groups were combined. Data is presented as mean (SD).</p

Percent non-contractile content (NCC) in leg muscles of Ctrl and DMD in different age groups.

<p>NCC of leg muscles of DMD at the age of >10 years was significantly different from 5–7.9 and 8–9.9 years age groups (denoted by #, p<0.05). NCC of TA, EDL, Per, MG, and SOL of DMD were significantly different than Ctrl in > 10 year age group (denoted by *, p<0.05). Additionally, only MG showed significant differences between DMD and Ctrl group at the age of 8–9.9 year. Data is presented as mean (SD).</p